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<TITLE>GNAT User's Guide</TITLE>
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<H1>GNAT User's Guide</H1>
<H2>GNAT, The GNU Ada 95 Compiler</H2>
<H2>Document revision level Document revision level 1.242 $</H2>
<H2>GNAT Version 3.12p </H2>
<H2>Date: $Date: 1999/06/28 18:09:34 $</H2>
<ADDRESS>Ada Core Technologies, Inc.</ADDRESS>
<P>
<P><HR><P>

<P>
(C) Copyright 1995-1999, Ada Core Technologies, Inc.

</P>
<P>
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.

</P>

<P>
Silicon Graphics and IRIS are registered trademarks
and IRIX is a trademark of Silicon Graphics, Inc.

</P>
<P>
IBM PC is a trademark of International
Business Machines Corporation.

</P>
<P>
UNIX is a registered trademark of AT&#38;T
Bell Laboratories.

</P>
<P>
The following are trademarks of Compaq Computers:
DEC, DEC Ada, DECthreads, DIGITAL, DECset, OpenVMS, and VAX.

</P>
<P>
The following are trademarks of Microsoft Corporation:
Windows NT, Windows 95, Windows 98.

</P>
<P>
The following are trademarks of Wind River Systems:
VxWorks, Tornado.

</P>



<H1><A NAME="SEC1" HREF="gnat_ug_toc.html#TOC1">About This Guide</A></H1>

<P>
This guide describes the use of GNAT, a compiler and software development
toolset for the full Ada 95 programming language.
It describes the features of the compiler and tools, and details
how to use them to build Ada 95 applications.

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC2">What This Guide Contains</A>
<LI><A HREF="gnat_ug.html#SEC3">What You Should Know Before Reading This Guide</A>
<LI><A HREF="gnat_ug.html#SEC4">Related Information</A>
<LI><A HREF="gnat_ug.html#SEC5">Conventions</A>
</UL>



<H2><A NAME="SEC2" HREF="gnat_ug_toc.html#TOC2">What This Guide Contains</A></H2>

<P>
This guide contains the following chapters:

<UL>
<LI>

section <A HREF="gnat_ug.html#SEC6">Getting Started With GNAT</A>, describes how to get started compiling
and running Ada programs with the GNAT Ada programming environment.
<LI>

section <A HREF="gnat_ug.html#SEC11">The GNAT Compilation Model</A>, describes the compilation model used
by GNAT.
<LI>

section <A HREF="gnat_ug.html#SEC33">Compiling Using <CODE>gcc</CODE></A>, describes how to compile
Ada programs with <CODE>gcc</CODE>, the Ada compiler.
<LI>

section <A HREF="gnat_ug.html#SEC52">Binding Using <CODE>gnatbind</CODE></A>, describes how to
perform binding of Ada programs with <CODE>gnatbind</CODE>, the GNAT binding
utility.
<LI>

section <A HREF="gnat_ug.html#SEC64">Linking Using <CODE>gnatlink</CODE></A>,
describes <CODE>gnatlink</CODE>, a
program that provides for linking using the GNAT run-time library to
construct a program. <CODE>gnatlink</CODE> can also incorporate foreign language
object units into the executable.
<LI>

section <A HREF="gnat_ug.html#SEC67">The GNAT Make Program <CODE>gnatmake</CODE></A>, describes <CODE>gnatmake</CODE>, a
utility that automatically determines the set of sources
needed by an Ada compilation unit, and executes the necessary compilations
binding and link.
<LI>

section <A HREF="gnat_ug.html#SEC75">Renaming Files Using <CODE>gnatchop</CODE></A>, describes
<CODE>gnatchop</CODE>, a utility that allows you to preprocess a file that
contains Ada source code, and split it into one or more new files, one
for each compilation unit.
<LI>

section <A HREF="gnat_ug.html#SEC94">The cross-referencing tools <CODE>gnatxref</CODE> and <CODE>gnatfind</CODE></A>, discusses
<CODE>gnatxref</CODE> and <CODE>gnatfind</CODE>, two tools that provide an easy
way to navigate through sources.
<LI>

section <A HREF="gnat_ug.html#SEC103">File Name Krunching Using <CODE>gnatkr</CODE></A>, describes the <CODE>gnatkr</CODE>
file name krunching utility, used to handle shortened
file names on operating systems with a limit on the length of names.
<LI>

section <A HREF="gnat_ug.html#SEC108">Preprocessing Using <CODE>gnatprep</CODE></A>, describes <CODE>gnatprep</CODE>, a
preprocessor utility that allows a single source file to be used to
generate multiple or parameterized source files, by means of macro
substitution.
<LI>

section <A HREF="gnat_ug.html#SEC113">The GNAT library browser <CODE>gnatls</CODE></A>, describes <CODE>gnatls</CODE>, a
utility that displays information about compiled units, including dependences
on the corresponding sources files, and consistency of compilations.
<LI>

section <A HREF="gnat_ug.html#SEC117">Rebuilding the GNAT Library</A>, describe the process of rebuilding
the GNAT library.

<LI>

section <A HREF="gnat_ug.html#SEC118">Finding memory problems with <CODE>gnatmem</CODE></A>, describes <CODE>gnatmem</CODE>, a
utility that monitors dynamic allocation and deallocation activity in a
program, and displays information about incorrect deallocations and sources
of possible memory leaks.
<LI>

section <A HREF="gnat_ug.html#SEC123">ASIS-Based Tools</A>, gives the general idea about the tools built
on top of the ASIS implementation for GNAT.
<LI>

section <A HREF="gnat_ug.html#SEC126">Creating Sample Bodies Using <CODE>gnatstub</CODE></A>, discusses <CODE>gnatstub</CODE>,
a utility that generates empty, but compilable bodies for library units.
<LI>

section <A HREF="gnat_ug.html#SEC129">Minimizing Executables for Ada Programs Using <CODE>gnatelim</CODE></A>, discusses
<CODE>gnatelim</CODE>, a tool which detects unused subprograms and produces
information that helps the compiler to create a smaller executable for a
program.
<LI>

section <A HREF="gnat_ug.html#SEC137">Other Utility Programs</A>, discusses several other GNAT utilities,
including <CODE>gnatpsta</CODE> and <CODE>gnatpsys</CODE>.
<LI>

section <A HREF="gnat_ug.html#SEC148">Running and Debugging Ada Programs</A>, describes how to run and debug
Ada programs.

<LI>

section <A HREF="gnat_ug.html#SEC27">Building mixed Ada &#38; C++ programs</A>, gives hints on how to interface
with c++.

<LI>

section <A HREF="gnat_ug.html#SEC160">Performance Considerations</A>, reviews the trade offs between using
defaults or options in program development.
</UL>



<H2><A NAME="SEC3" HREF="gnat_ug_toc.html#TOC3">What You Should Know Before Reading This Guide</A></H2>

<P>
<A NAME="IDX1"></A>
This user's guide assumes that you are familiar with Ada 95 language, as
described in the International Standard ANSI/ISO/IEC-8652:1995, Jan
1995.

</P>


<H2><A NAME="SEC4" HREF="gnat_ug_toc.html#TOC4">Related Information</A></H2>

<P>
For further information about related tools, refer to the following
documents:

</P>

<UL>
<LI>

<CITE>GNAT Reference Manual</CITE>, which contains all reference
material for the GNAT implementation of Ada 95.

<LI>

<CITE>Ada 95 Language Reference Manual</CITE>, which contains all reference
material for the Ada 95 programming language.

<LI>

<CITE>Debugging with GDB</CITE>
contains all details on the use of the GNU source-level debugger.

<LI>

<CITE>GNU Emacs Manual</CITE>
contains full information on the extensible editor and programming
environment Emacs.

</UL>



<H2><A NAME="SEC5" HREF="gnat_ug_toc.html#TOC5">Conventions</A></H2>
<P>
<A NAME="IDX2"></A>
<A NAME="IDX3"></A>

</P>
<P>
Following are examples of the typographical and graphic conventions used
in this guide:

</P>

<UL>
<LI>

<CODE>Functions</CODE>, <CODE>utility program names</CODE>, <CODE>standard names</CODE>,
and <CODE>classes</CODE>.

<LI>

<SAMP>`Option flags'</SAMP>

<LI>

<TT>`File Names'</TT>, <TT>`button names'</TT>, and <TT>`field names'</TT>.

<LI>

<VAR>Variables</VAR>.

<LI>

<EM>Emphasis</EM>.

<LI>

[optional information or parameters]

<LI>

Examples are described by text

<PRE>
and then shown this way.
</PRE>

</UL>

<P>
Commands that are entered by the user are preceded in this manual by the
characters "<CODE>$ </CODE>" (dollar sign followed by space). If your system
uses this sequence as a prompt, then the commands will appear exactly as
you see them in the manual. If your system uses some other prompt, then
the command will appear with the <CODE>$</CODE> replaced by whatever prompt
character you are using.

</P>



<H1><A NAME="SEC6" HREF="gnat_ug_toc.html#TOC6">Getting Started With GNAT</A></H1>

<P>
This chapter describes the simplest ways of using GNAT to compile Ada
programs.

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC7">Running GNAT</A>
<LI><A HREF="gnat_ug.html#SEC8">Running a Simple Ada Program</A>
<LI><A HREF="gnat_ug.html#SEC9">Running a Program With Multiple Units</A>
<LI><A HREF="gnat_ug.html#SEC10">Using the gnatmake Utility</A>
</UL>



<H2><A NAME="SEC7" HREF="gnat_ug_toc.html#TOC7">Running GNAT</A></H2>

<P>
Three steps are needed to create an executable file from an Ada source
file:

</P>

<OL>
<LI>

The source file(s) must be compiled.
<LI>

The file(s) must be bound using the GNAT binder.
<LI>

All appropriate object files must be linked to produce an executable.
</OL>

<P>
All three steps are most commonly handled by using the <CODE>gnatmake</CODE>
utility program that, given the name of the main program, automatically
performs the necessary compilation, binding and linking steps.

</P>


<H2><A NAME="SEC8" HREF="gnat_ug_toc.html#TOC8">Running a Simple Ada Program</A></H2>

<P>
Any editor may be used to prepare an Ada program. If <CODE>emacs</CODE> is
used, the optional Ada mode may be helpful in laying out the program. The
program text is a normal text file. We will suppose in our initial
example that you have used your editor to prepare the following
standard format text file:

</P>

<PRE>
   <B>with</B> Text_IO; <B>use</B> Text_IO;
   <B>procedure</B> Hello <B>is</B>
   <B>begin</B>
      Put_Line ("Hello WORLD!");
   <B>end</B> Hello;
</PRE>

<P>
This file should be named <TT>`hello.adb'</TT>.
Using the normal default file naming conventions, By default, GNAT requires
that each file
contain a single compilation unit whose file name corresponds to the
unit name
with periods replaced by hyphens, and whose
extension is <TT>`.ads'</TT> for a
spec and <TT>`.adb'</TT> for a body.
This default file naming convention can be overridden by use of the
special pragma <CODE>Source_File_Name</CODE> see section <A HREF="gnat_ug.html#SEC18">Using Other File Names</A>.
Alternatively, if you want to rename your files according to this default
convention, which is probably more convenient if you will be using GNAT
for all your compilation requirements, then the <CODE>gnatchop</CODE> utility
can be used to perform this renaming operation
(see section <A HREF="gnat_ug.html#SEC75">Renaming Files Using <CODE>gnatchop</CODE></A>).

</P>
<P>
You can compile the program using the following command:

</P>

<PRE>
   $ gcc -c hello.adb
</PRE>

<P>
<CODE>gcc</CODE> is the command used to run the compiler. This compiler is
capable of compiling programs in several languages including Ada 95 and
C.  It determines you have given it an Ada program by the extension
(<TT>`.ads'</TT> or <TT>`.adb'</TT>), and will call the GNAT compiler to compile
the specified file.

</P>
<P>
The <CODE>-c</CODE> switch is required.  It tells <CODE>gcc</CODE> to only do a
compilation. (For C programs, <CODE>gcc</CODE> can also do linking, but this
capability is not used directly for Ada programs, so the <CODE>-c</CODE>
switch must always be present.)

</P>
<P>
This compile command generates a file
<TT>`hello.o'</TT> which is the object
file corresponding to your Ada program. It also generates a file
<TT>`hello.ali'</TT>
which contains additional information used to check
that an Ada program is consistent. To get an executable file,
we then use <CODE>gnatbind</CODE> to bind the program
and <CODE>gnatlink</CODE> to link it to produce the executable. The
argument to both gnatbind and gnatlink is the name of the
<TT>`ali'</TT> file, but the default extension of <TT>`.ali'</TT> can
be omitted. This means that in the most common case, the argument
is simply the name of the main program:

</P>

<PRE>
   $ gnatbind hello
   $ gnatlink hello
</PRE>

<P>
A simpler method of carrying out these steps is to use
<CODE>gnatmake</CODE>, which
is a master program which invokes all of the required
compilation, binding and linking tools in the correct order. In particular,
<CODE>gnatmake</CODE> automatically recompiles any sources that have been modified
since they were last compiled, or sources that depend
on such modified sources, so that a consistent compilation is ensured.

</P>

<PRE>
   $ gnatmake hello.adb
</PRE>

<P>
The result is an executable program called <TT>`hello'</TT>, which can be
run by entering:

</P>

<PRE>
   $ ./hello
</PRE>

<P>
and, if all has gone well, you will see

</P>

<PRE>
   Hello WORLD!
</PRE>

<P>
appear in response to this command.

</P>


<H2><A NAME="SEC9" HREF="gnat_ug_toc.html#TOC9">Running a Program With Multiple Units</A></H2>

<P>
Consider a slightly more complicated example that has three files: a
main program, and the spec and body of a package:

</P>

<PRE>
   <B>package</B> Greetings <B>is</B>
      <B>procedure</B> Hello;
      <B>procedure</B> Goodbye;
   <B>end</B> Greetings;

   <B>with</B> Text_IO; <B>use</B> Text_IO;
   <B>package</B> <B>body</B> Greetings <B>is</B>
      <B>procedure</B> Hello <B>is</B>
      <B>begin</B>
         Put_Line ("Hello WORLD!");
      <B>end</B> Hello;
      <B>procedure</B> Goodbye <B>is</B>
      <B>begin</B>
         Put_Line ("Goodbye WORLD!");
      <B>end</B> Goodbye;
   <B>end</B> Greetings;

   <B>with</B> Greetings;
   <B>procedure</B> Gmain <B>is</B>
   <B>begin</B>
      Greetings.Hello;
      Greetings.Goodbye;
   <B>end</B> Gmain;
</PRE>

<P>
Following the one-unit-per-file rule, place this program in the
following three separate files:

</P>
<DL COMPACT>

<DT><TT>`greetings.ads'</TT>
<DD>
spec of package <CODE>Greetings</CODE>

<DT><TT>`greetings.adb'</TT>
<DD>
body of package <CODE>Greetings</CODE>

<DT><TT>`gmain.adb'</TT>
<DD>
body of main program
</DL>

<P>
To build an executable version of
this program, we could use four separate steps to compile, bind, and link
the program, as follows:

</P>

<PRE>
   $ gcc -c gmain.adb
   $ gcc -c greetings.adb
   $ gnatbind gmain
   $ gnatlink gmain
</PRE>

<P>
Note that there is no required order of compilation when using GNAT.
In particular it is perfectly fine to compile the main program first.
Also, it is not necessary to compile package specs in the case where
there is a separate body, only the body need be compiled. If you want
to submit these programs to the compiler for semantic checking purposes,
then you use the
<CODE>-gnatc</CODE> switch:

</P>

<PRE>
   $ gcc -c greetings.ads -gnatc
</PRE>

<P>
Although the compilation can be done in separate steps as in the
above example, in practice it is almost always more convenient
to use the <CODE>gnatmake</CODE> capability. All you need to know in this case
is the name of the main program source file. The effect of the above four
commands can be achieved with a single one:

</P>

<PRE>
   $ gnatmake gmain.adb
</PRE>

<P>

</P>
<P>
In the next section we discuss the advantages of using <CODE>gnatmake</CODE> in
more detail.

</P>


<H2><A NAME="SEC10" HREF="gnat_ug_toc.html#TOC10">Using the <CODE>gnatmake</CODE> Utility</A></H2>

<P>
If you work on a program by compiling single components at a time using
<CODE>gcc</CODE>, you typically keep track of the units you modify. In order to
build a consistent system, you compile not only these units, but also any
units that depend on the units you have modified.
For example, in the preceding case,
if you edit <TT>`gmain.adb'</TT>, you only need to recompile that file. But if
you edit <TT>`greetings.ads'</TT>, you must recompile both
<TT>`greetings.adb'</TT> and <TT>`gmain.adb'</TT>, because both files contain
units that depend on <TT>`greetings.ads'</TT>.

</P>
<P>
<CODE>gnatbind</CODE> will warn you if you forget one of these compilation
steps, so that it is impossible to generate an inconsistent program as a
result of forgetting to do a compilation. Nevertheless it is tedious and
error-prone to keep track of dependencies among units.
One approach to handle the dependency-bookkeeping is to use a
makefile. However, makefiles present maintenance problems of their own:
if the dependencies change as you change the program, you must make
sure that the makefile is kept up-to-date manually, which is also an
error-prone process.

</P>
<P>
The <CODE>gnatmake</CODE> utility takes care of these details automatically.
Invoke it using either one of the following forms:

</P>

<PRE>
   $ gnatmake gmain.adb
   $ gnatmake gmain
</PRE>

<P>
The argument is the name of the file containing the main program from
which you may omit the extension. <CODE>gnatmake</CODE>
examines the environment, automatically recompiles any files that need
recompiling, and binds and links the resulting set of object files,
generating the executable file, <TT>`gmain'</TT>.
In a large program, it
can be extremely helpful to use <CODE>gnatmake</CODE>, because working out by hand
what needs to be recompiled can be difficult.

</P>
<P>
Note that <CODE>gnatmake</CODE>
takes into account all the intricate Ada 95 rules that
establish dependencies among units. These include dependencies that result
from inlining subprogram bodies, and from
generic instantiation. Unlike some other
Ada make tools, <CODE>gnatmake</CODE> does not rely on the dependencies that were
found by the compiler on a previous compilation, which may possibly
be wrong when sources change. <CODE>gnatmake</CODE> determines the exact set of
dependencies from scratch each time it is run.

</P>



<H1><A NAME="SEC11" HREF="gnat_ug_toc.html#TOC11">The GNAT Compilation Model</A></H1>
<P>
<A NAME="IDX4"></A>
<A NAME="IDX5"></A>

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC12">Source Representation</A>
<LI><A HREF="gnat_ug.html#SEC13">Foreign Language Representation</A>
<LI><A HREF="gnat_ug.html#SEC17">File Naming Rules</A>
<LI><A HREF="gnat_ug.html#SEC18">Using Other File Names</A>
<LI><A HREF="gnat_ug.html#SEC19">Generating Object Files</A>
<LI><A HREF="gnat_ug.html#SEC20">Source Dependencies</A>
<LI><A HREF="gnat_ug.html#SEC21">The Ada Library Information Files</A>
<LI><A HREF="gnat_ug.html#SEC22">Representation of Time Stamps</A>
<LI><A HREF="gnat_ug.html#SEC23">Binding an Ada Program</A>
<LI><A HREF="gnat_ug.html#SEC24">Mixed Language Programming</A>
<LI><A HREF="gnat_ug.html#SEC27">Building mixed Ada &#38; C++ programs</A>
<LI><A HREF="gnat_ug.html#SEC31">Comparison between GNAT and C/C++ Compilation Models</A>
<LI><A HREF="gnat_ug.html#SEC32">Comparison between GNAT and Conventional Ada Library Models</A>
</UL>

<P>
This chapter describes the compilation model used by GNAT. Although
similar to that used by other languages, such as C and C++, this model
is substantially different from the traditional Ada compilation models,
which are based on a library.  The model is initially described without
reference to the library-based model. If you have not previously used an
Ada compiler, you need only read the first part of this chapter.  The
last section describes and discusses the differences between the GNAT
model and the traditional Ada compiler models. If you have used other
Ada compilers, this section will help you to understand those
differences, and the advantages of the GNAT model.

</P>


<H2><A NAME="SEC12" HREF="gnat_ug_toc.html#TOC12">Source Representation</A></H2>
<P>
<A NAME="IDX6"></A>

</P>
<P>
Ada source programs are represented in standard text files, using
Latin-1 coding. Latin-1 is an 8-bit code that includes the familiar
7-bit ASCII set, plus additional characters used for
representing foreign languages (see section <A HREF="gnat_ug.html#SEC13">Foreign Language Representation</A>
for support of non-USA character sets). The format effector characters
are represented using their standard ASCII encodings, as follows:

</P>
<DL COMPACT>

<DT><CODE>VT</CODE>
<DD>
<A NAME="IDX7"></A>
Vertical tab, <CODE>16#0B#</CODE>

<DT><CODE>HT</CODE>
<DD>
<A NAME="IDX8"></A>
Horizontal tab, <CODE>16#09#</CODE>

<DT><CODE>CR</CODE>
<DD>
<A NAME="IDX9"></A>
Carriage return, <CODE>16#0D#</CODE>

<DT><CODE>LF</CODE>
<DD>
<A NAME="IDX10"></A>
Line feed, <CODE>16#0A#</CODE>

<DT><CODE>FF</CODE>
<DD>
<A NAME="IDX11"></A>
Form feed, <CODE>16#0C#</CODE>
</DL>

<P>
Source files are in standard text file format. In addition, GNAT will
recognize a wide variety of stream formats, in which the end of physical
physical lines is marked by any of the following sequences:
<CODE>LF</CODE>, <CODE>CR</CODE>, <CODE>CR-LF</CODE>, or <CODE>LF-CR</CODE>. This is useful
in accommodating files that are imported from other operating systems.

</P>
<P>
<A NAME="IDX12"></A>
<A NAME="IDX13"></A>
<A NAME="IDX14"></A>
The end of a source file is normally represented by the physical end of
file. However, the control character <CODE>16#1A#</CODE> (<CODE>SUB</CODE>) is also
recognized as signalling the end of the source file. Again, this is
provided for compatibility with other operating systems where this
code is used to represent the end of file.

</P>
<P>
Each file contains a single Ada compilation unit, including any pragmas
associated with the unit. For example, this means you must place a
package declaration (a package <STRONG>spec</STRONG>) and the corresponding body in
separate files. An Ada <STRONG>compilation</STRONG> (which is a sequence of
compilation units) is represented using a sequence of files. Similarly,
you will place each subunit or child unit in a separate file.

</P>


<H2><A NAME="SEC13" HREF="gnat_ug_toc.html#TOC13">Foreign Language Representation</A></H2>

<P>
GNAT supports the standard character sets defined in Ada 95 as well as
several other non-standard character sets for use in localized versions
of the compiler (see section <A HREF="gnat_ug.html#SEC44">Character Set Control</A>).

<UL>
<LI><A HREF="gnat_ug.html#SEC14">Latin-1</A>
<LI><A HREF="gnat_ug.html#SEC15">Other 8-Bit Codes</A>
<LI><A HREF="gnat_ug.html#SEC16">Wide Character Encodings</A>
</UL>



<H3><A NAME="SEC14" HREF="gnat_ug_toc.html#TOC14">Latin-1</A></H3>
<P>
<A NAME="IDX15"></A>

</P>
<P>
The basic character set is Latin-1. This character set is defined by ISO
standard 8859, part 1. The lower half (character codes <CODE>16#00#</CODE>
... <CODE>16#7F#)</CODE> is identical to standard ASCII coding, but the upper half is
used to represent additional characters. These include extended letters
used by European languages, such as French accents, the vowels with umlauts
used in German, and the extra letter A-ring used in Swedish.

</P>
<P>
<A NAME="IDX16"></A>
For a complete list of Latin-1 codes and their encodings, see the source
file of library unit <CODE>Ada.Characters.Latin_1</CODE> in file
<TT>`a-chlat1.ads'</TT>.
You may use any of these extended characters freely in character or
string literals. In addition, the extended characters that represent
letters can be used in identifiers.

</P>


<H3><A NAME="SEC15" HREF="gnat_ug_toc.html#TOC15">Other 8-Bit Codes</A></H3>

<P>
GNAT also supports several other 8-bit coding schemes:

</P>
<DL COMPACT>

<DT>Latin-2
<DD>
<A NAME="IDX17"></A>
 
Latin-2 letters allowed in identifiers, with uppercase and lowercase
equivalence.

<DT>Latin-3
<DD>
<A NAME="IDX18"></A>
Latin-3 letters allowed in identifiers, with uppercase and lowercase
equivalence.

<DT>Latin-4
<DD>
<A NAME="IDX19"></A>
Latin-4 letters allowed in identifiers, with uppercase and lowercase
equivalence.

<DT>IBM PC (code page 437)
<DD>
<A NAME="IDX20"></A>
This code page is the normal default for PCs in the U.S. It corresponds
to the original IBM PC character set. This set has some, but not all, of
the extended Latin-1 letters, but these letters do not have the same
encoding as Latin-1. In this mode, these letters are allowed in
identifiers with uppercase and lowercase equivalence.

<DT>IBM PC (code page 850)
<DD>
<A NAME="IDX21"></A>
This code page is a modification of 437 extended to include all the
Latin-1 letters, but still not with the usual Latin-1 encoding. In this
mode, all these letters are allowed in identifiers with uppercase and
lowercase equivalence.

<DT>Full Upper 8-bit
<DD>
Any character in the range 80-FF allowed in identifiers, and all are
considered distinct.  In other words, there are no uppercase and lowercase
equivalences in this range. This is useful in conjunction with
certain encoding schemes used for some foreign character sets (e.g.
the typical method of representing Chinese characters on the PC).

<DT>No Upper-Half
<DD>
No upper-half characters in the range 80-FF are allowed in identifiers.
This gives Ada 83 compatibility for identifier names.
</DL>

<P>
For precise data on the encodings permitted, and the uppercase and lowercase
equivalences that are recognized, see the file <TT>`csets.adb'</TT> in
the GNAT compiler sources. You will need to obtain a full source release
of GNAT to obtain this file.

</P>


<H3><A NAME="SEC16" HREF="gnat_ug_toc.html#TOC16">Wide Character Encodings</A></H3>

<P>
GNAT allows wide character codes to appear in character and string
literals, and also optionally in identifiers, by means of the following
possible encoding schemes:

</P>
<DL COMPACT>

<DT>Hex Coding
<DD>
In this encoding, a wide character is represented by the following five
character sequence:


<PRE>
   ESC a b c d
</PRE>

Where <CODE>a</CODE>, <CODE>b</CODE>, <CODE>c</CODE>, <CODE>d</CODE> are the four hexadecimal
characters (using uppercase letters) of the wide character code. For
example, ESC A345 is used to represent the wide character with code
<CODE>16#A345#</CODE>.
This scheme is compatible with use of the full Wide_Character set.

<DT>Upper-Half Coding
<DD>
<A NAME="IDX22"></A>
The wide character with encoding <CODE>16#abcd#</CODE> where the upper bit is on (in
other words, "a" is in the range 8-F) is represented as two bytes,
<CODE>16#ab#</CODE> and <CODE>16#cd#</CODE>. The second byte cannot be a format control
character, but is not required to be in the upper half. This method can
be also used for shift-JIS or EUC, where the internal coding matches the
external coding.

<DT>Shift JIS Coding
<DD>
<A NAME="IDX23"></A>
A wide character is represented by a two-character sequence,
<CODE>16#ab#</CODE> and
<CODE>16#cd#</CODE>, with the restrictions described for upper-half encoding as
described above. The internal character code is the corresponding JIS
character according to the standard algorithm for Shift-JIS
conversion. Only characters defined in the JIS code set table can be
used with this encoding method.

<DT>EUC Coding
<DD>
<A NAME="IDX24"></A>
A wide character is represented by a two-character sequence
<CODE>16#ab#</CODE> and
<CODE>16#cd#</CODE>, with both characters being in the upper half. The internal
character code is the corresponding JIS character according to the EUC
encoding algorithm. Only characters defined in the JIS code set table
can be used with this encoding method.

<DT>UTF-8 Coding
<DD>
A wide character is represented using
UCS Transformation Format 8 (UTF-8) as defined in Annex R of ISO
10646-1/Am.2.  Depending on the character value, the representation
is a one, two, or three byte sequence:


<PRE>
   16#0000#-16#007f#: 2#0xxxxxxx#
   16#0080#-16#07ff#: 2#110xxxxx# 2#10xxxxxx#
   16#0800#-16#ffff#: 2#1110xxxx# 2#10xxxxxx# 2#10xxxxxx#
</PRE>

where the xxx bits correspond to the left-padded bits of the
16-bit character value. Note that all lower half ASCII characters
are represented as ASCII bytes and all upper half characters and
other wide characters are represented as sequences of upper-half
(The full UTF-8 scheme allows for encoding 31-bit characters as
6-byte sequences, but in this implementation, all UTF-8 sequences
of four or more bytes length will be treated as illegal).
<DT>Brackets Coding
<DD>
In this encoding, a wide character is represented by the following eight
character sequence:


<PRE>
   [ " a b c d " ]
</PRE>

Where <CODE>a</CODE>, <CODE>b</CODE>, <CODE>c</CODE>, <CODE>d</CODE> are the four hexadecimal
characters (using uppercase letters) of the wide character code. For
example, ["A345"] is used to represent the wide character with code
<CODE>16#A345#</CODE>. It is also possible (though not required) to use the
Brackets coding for upper half characters. For example, the code
<CODE>16#A3#</CODE> can be represented as <CODE>["A3"]</CODE>.

This scheme is compatible with use of the full Wide_Character set,
and is also the method used for wide character encoding in the standard
ACVC (Ada Compiler Validation Capability) test suite distributions.

</DL>

<P>
Note: Some of these coding schemes do not permit the full use of the
Ada 95 character set. For example, neither Shift JIS, nor EUC allow the
use of the upper half of the Latin-1 set.

</P>


<H2><A NAME="SEC17" HREF="gnat_ug_toc.html#TOC17">File Naming Rules</A></H2>

<P>
The default file name is determined by the name of the unit that the
file contains.  The name is formed by taking the full expanded name of
the unit and replacing the separating dots with hyphens and using
lowercase for all letters.

</P>
<P>
An exception arises if the file name generated by the above rules starts
with one of the characters
a,g,i, or s,
and the second character is a
minus.  In this case, the character tilde is used in place
of the minus.  The reason for this special rule is to avoid clashes with
the standard names for child units of the packages System, Ada,
Interfaces, and GNAT, which use the prefixes
s- a- i- and g-
respectively.

</P>
<P>
The file extension is <TT>`.ads'</TT> for a spec and
<TT>`.adb'</TT> for a body. The following list shows some
examples of these rules.

</P>
<DL COMPACT>

<DT><TT>`main.ads'</TT>
<DD>
Main (spec)
<DT><TT>`main.adb'</TT>
<DD>
Main (body)
<DT><TT>`arith_functions.ads'</TT>
<DD>
Arith_Functions (package spec)
<DT><TT>`arith_functions.adb'</TT>
<DD>
Arith_Functions (package body)
<DT><TT>`func-spec.ads'</TT>
<DD>
Func.Spec (child package spec)
<DT><TT>`func-spec.adb'</TT>
<DD>
Func.Spec (child package body)
<DT><TT>`main-sub.adb'</TT>
<DD>
Sub (subunit of Main)
<DT><TT>`a~bad.adb'</TT>
<DD>
A.Bad (child package body)
</DL>

<P>
Following these rules can result in excessively long
file names if corresponding
unit names are long (for example, if child units or subunits are
heavily nested). An option is available to shorten such long file names
(called file name "krunching"). This may be particularly useful when
programs being developed with GNAT are to be used on operating systems
with limited file name lengths.  See section <A HREF="gnat_ug.html#SEC105">Using <CODE>gnatkr</CODE></A>.

</P>
<P>
Of course, no file shortening algorithm can guarantee uniqueness over
all possible unit names; if file name krunching is used, it is your
responsibility to ensure no name clashes occur. Alternatively you
can specify the exact file names that you want used, as described
in the next section. Finally, if your Ada programs are migrating from a
compiler with a different naming convention, you can use the gnatchop
utility to produce source files that follow the GNAT naming conventions.
(For details see section <A HREF="gnat_ug.html#SEC75">Renaming Files Using <CODE>gnatchop</CODE></A>.)

</P>


<H2><A NAME="SEC18" HREF="gnat_ug_toc.html#TOC18">Using Other File Names</A></H2>
<P>
<A NAME="IDX25"></A>

</P>
<P>
In the previous section, we have described the default rules used by
GNAT to determine the file name in which a given unit resides. It is
often convenient to follow these default rules, and if you follow them,
the compiler knows without being explicitly told where to find all
the files it needs.

</P>
<P>
However, in some cases, particularly when a program is imported from
another Ada compiler environment, it may be more convenient for the
programmer to specify which file names contain which units. GNAT allows
arbitrary file names to be used by means of the Source_File_Name pragma.
The form of this pragma is as shown in the following examples:
<A NAME="IDX26"></A>

</P>

<PRE>
   <B>pragma</B> Source_File_Name (My_Utilities.Stacks,
     Spec_File_Name =&#62; "myutilst_a.ada");
   <B>pragma</B> Source_File_name (My_Utilities.Stacks,
     Body_File_Name =&#62; "myutilst.ada");
</PRE>

<P>
As shown in this example, the first argument for the pragma is the unit
name (in this example a child unit). The second argument has the form
of a named association.  The identifier
indicates whether the file name is for a spec or a body;
the file name itself is given by a string literal.

</P>
<P>
The source file name pragma is a configuration pragma, which means that
normally it will be placed in the <TT>`gnat.adc'</TT>
file used to hold configuration
pragmas that apply to a complete compilation environment.
For more details on how the <TT>`gnat.adc'</TT> file is created and used
see section <A HREF="gnat_ug.html#SEC82">Handling of Configuration Pragmas</A>
<A NAME="IDX27"></A>

</P>
<P>
GNAT allows completely arbitrary file names to be specified using the
source file name pragma. However, if the file name specified has an
extension other than <TT>`.ads'</TT> or <TT>`.adb'</TT> it is necessary to use a special
syntax when compiling the file. The name in this case must be preceded
by the special sequence <CODE>-x</CODE> followed by a space and the name of the
language, here <CODE>ada</CODE>, as in:

</P>

<PRE>
   $ gcc -c -x ada peculiar_file_name.sim
</PRE>

<P>
<CODE>gnatmake</CODE> handles non-standard file names in the usual manner (the
non-standard file name for the main program is simply used as the
argument to gnatmake). Note that if the extension is also non-standard,
then it must be included in the gnatmake command, it may not be omitted.

</P>


<H2><A NAME="SEC19" HREF="gnat_ug_toc.html#TOC19">Generating Object Files</A></H2>

<P>
An Ada program consists of a set of source files, and the first step in
compiling the program is to generate the corresponding object files.
These are generated by compiling a subset of these source files.
The files you need to compile are the following:

</P>

<UL>
<LI>

If a package spec has no body, compile the package spec to produce the
object file for the package.

<LI>

If a package has both a spec and a body, compile the body to produce the
object file for the package. The source file for the package spec need
not be compiled in this case because there is only one object file, which
contains the code for both the spec and body of the package.

<LI>

For a subprogram, compile the subprogram body to produce the object file
for the subprogram. The spec, if one is present, is as usual in a
separate file, and need not be compiled.

<LI>

<A NAME="IDX28"></A>
In the case of subunits, only compile the parent unit.  A single object
file is generated for the entire subunit tree, which includes all the
subunits.

<LI>

Compile child units independently of their parent units
(though, of course, the spec of all the ancestor unit must be present in order
to compile a child unit).

<LI>

<A NAME="IDX29"></A>
Compile generic units in the same manner as any other units. The object
files in this case are small dummy files that contain at most the
flag used for elaboration checking. This is because GNAT always handles generic
instantiation by means of macro expansion. However, it is still necessary to
compile generic units, for dependency checking and elaboration purposes.
</UL>

<P>
The preceding rules describe the set of files that must be compiled to
generate the object files for a program. Each object file has the same
name as the corresponding source file, except that the extension is
<TT>`.o'</TT> as usual.

</P>
<P>
You may wish to compile other files for the purpose of checking their
syntactic and semantic correctness. For example, in the case where a
package has a separate spec and body, you would not normally compile the
spec.  However, it is convenient in practice to compile the spec to make
sure it is error-free before compiling clients of this spec, because such
compilations will fail if there is an error in the spec.

</P>
<P>
GNAT provides an option for compiling such files purely for the
purposes of checking correctness; such compilations are not required as
part of the process of building a program. To compile a file in this
checking mode, use the <CODE>-gnatc</CODE> switch.

</P>


<H2><A NAME="SEC20" HREF="gnat_ug_toc.html#TOC20">Source Dependencies</A></H2>

<P>
A given object file clearly depends on the source file which is compiled
to produce it. Here we are using <STRONG>depends</STRONG> in the sense of a typical
<CODE>make</CODE> utility; in other words, an object file depends on a source
file if changes to the source file require the object file to be
recompiled.
In addition to this basic dependency, a given object may depend on
additional source files as follows:

</P>

<UL>
<LI>

If a file being compiled <CODE>with</CODE>'s a unit <VAR>X</VAR>, the object file
depends on the file containing the spec of unit <VAR>X</VAR>. This includes
files that are <CODE>with</CODE>'ed implicitly either because they are parents
of <CODE>with</CODE>'ed child units or they are run-time units required by the
language constructs used in a particular unit.

<LI>

If a file being compiled instantiates a library level generic unit, the
object file depends on both the spec and body files for this generic
unit.

<LI>

If a file being compiled instantiates a generic unit defined within a
package, the object file depends on the body file for the package as
well as the spec file.

<LI>

<A NAME="IDX30"></A>
<A NAME="IDX31"></A>
If a file being compiled contains a call to a subprogram for which
pragma <CODE>Inline</CODE> applies and inlining is activated with the
<CODE>-gnatn</CODE> switch, the object file depends on the file containing the
body of this subprogram as well as on the file containing the spec.
Similarly if the <CODE>-gnatN</CODE> switch is used, then the unit is
dependent on all body files.

<LI>

The object file for a parent unit depends on all its subunit body files.
</UL>

<P>
These rules are applied transitively: if unit <CODE>A</CODE> <CODE>with</CODE>'s
unit <CODE>B</CODE>, whose elaboration calls an inlined procedure in package
<CODE>C</CODE>, the object file for unit <CODE>A</CODE> will depend on the body of
<CODE>C</CODE>, in file <TT>`c.adb'</TT>.

</P>
<P>
The set of dependent files described by these rules includes all the
files on which the unit is semantically dependent, as described in the
Ada 95 Language Reference Manual. However, it is a superset of what the
ARM describes, because it includes generic, inline, and subunit dependencies.

</P>
<P>
An object file must be recreated by recompiling the corresponding source
file if any of the source files on which it depends are modified. For
example, if the <CODE>make</CODE> utility is used to control compilation,
the rule for an Ada object file must mention all the source files on
which the object file depends, according to the above definition.
The determination of the necessary
recompilations is done automatically when one uses <CODE>gnatmake</CODE>.

</P>


<H2><A NAME="SEC21" HREF="gnat_ug_toc.html#TOC21">The Ada Library Information Files</A></H2>

<P>
Each compilation actually generates two output files. The first of these
is the normal object file that has a <TT>`.o'</TT> extension. The second is a
text file containing full dependency information. It has the same
name as the source file, but an <TT>`.ali'</TT> extension.
This file is known as the Ada Library Information (ALI) file.

</P>
<P>
Normally you need not be concerned with the contents of this file.
This section is included in case you want to understand how these files
are being used by the binder and other GNAT utilities.
Each ALI file consists of a series of lines of the form:

</P>

<PRE>
   <VAR>Key_Character</VAR> <VAR>parameter</VAR> <VAR>parameter</VAR> ...
</PRE>

<P>
<A NAME="IDX32"></A>
The first two lines in the file identify the library output version and
<CODE>Standard</CODE> version. These are required to be consistent across the
entire set of compilation units in your program.

</P>

<PRE>
   V "<VAR>xxxxxxxxxxxxxxxx</VAR>"
</PRE>

<P>
This line indicates the library output version, as defined in
<TT>`gnatvsn.ads'</TT>.  It ensures that separate object modules of a
program are consistent. The library output version
must be changed if anything in the compiler changes that
would affect successful binding of modules compiled separately.
Examples of such changes are modifications in the format of the library
information described in this package, modifications to calling
sequences, or to the way data is represented.

</P>

<PRE>
   S "<VAR>xxxxxxxxxxxxxxxx</VAR>"
</PRE>

<P>
<A NAME="IDX33"></A>
<A NAME="IDX34"></A>
This line contains information regarding types declared in packages
<CODE>Standard</CODE> as stored in <CODE>Gnatvsn.Standard_Version</CODE>.
The purpose of this information is to ensure that all units in a
program are compiled with a consistent set of options.
This is critical on systems where, for example, the size of <CODE>Integer</CODE>
can be set by command line switches.

</P>

<PRE>
   M <VAR>type</VAR> [<VAR>priority</VAR>]
</PRE>

<P>
<A NAME="IDX35"></A>
This line is present only for a unit that can be a main program.
<VAR>type</VAR> is either <CODE>P</CODE> for a parameterless procedure or <CODE>F</CODE>
for a function returning a value of integral type.  The latter is for
writing a main program that returns an exit status. <VAR>priority</VAR> is
present only if there was a valid pragma <CODE>Priority</CODE> in the
corresponding unit to set the main task priority. It is an unsigned
decimal integer.

</P>

<PRE>
   F x
</PRE>

<P>
This line is present if a pragma Float_Representation or Long_Float is
used to specify other than the default floating-point format.
This option
applies only to implementations of GNAT for the Digital Alpha Systems.
The character
x is 'I' for IEEE_Float, 'G' for VAX_Float with Long_Float using G_Float,
and 'D' for VAX_Float for Long_Float with D_Float.

</P>

<PRE>
   P L=x Q=x T=x
</PRE>

<P>
This line is present if the unit uses tasking directly or indirectly, and
has one or more valid xxx_Policy pragmas that apply to the unit. The
arguments are as follows

</P>

<PRE>
   L=x (locking policy)
</PRE>

<P>
This is present if a valid Locking_Policy pragma applies to the unit. The
single character indicates the policy in effect
(e.g. <SAMP>`C'</SAMP> for Ceiling_Locking).

</P>

<PRE>
   Q=x (queuing policy)
</PRE>

<P>
This is present if a valid Queuing_Policy pragma applies to the unit. The
single character indicates the policy in effect (e.g. <SAMP>`P'</SAMP> for
Priority_Queuing).

</P>

<PRE>
   T=x (task_dispatching policy)
</PRE>

<P>
This is present if a valid
Task_Dispatching_Policy pragma applies to the unit. The
single character indicates the policy
in effect (e.g. <SAMP>`F'</SAMP> for
FIFO_Within_Priorities).

</P>
<P>
Following these header lines is a set of information lines, one per
compilation unit. Each line lists a unit in the object file corresponding
to this ALI file.
In particular, when a package body or subprogram body is compiled there
will be two such lines, one for the spec and one for the body,
with the entry for the body appearing first. This is the only case in
which a single ALI file contains more than one unit. Note that
subunits do not count as compilation units for this purpose, and
generate no library information, because they are inlined.
The lines for each compilation unit have the following form:

</P>

<PRE>
   U <VAR>unit-name</VAR> <VAR>source-name</VAR> <VAR>version</VAR> [<VAR>attributes</VAR>]
</PRE>

<P>
<A NAME="IDX36"></A>
This line identifies the unit to which this section of the library
information file applies. <VAR>unit-name</VAR> is the unit name in internal
format, as described in package <CODE>Uname</CODE>, and <VAR>source-name</VAR> is
the name of the source file containing the unit.

</P>
<P>
<VAR>version</VAR> is the version, given by eight hexadecimal characters with
lowercase letters. This value is a hash code that includes
contributions from the time stamps of this unit and all the units on which
it semantically depends.

</P>
<P>
The optional <VAR>attributes</VAR> are a series of two-letter codes
indicating information about the unit. They indicate the nature of
the unit and they summarize information provided by
categorization pragmas.

</P>
<DL COMPACT>

<DT><CODE>EB</CODE>
<DD>
<A NAME="IDX37"></A>
Unit has pragma Elaborate_Body.

<DT><CODE>NE</CODE>
<DD>
Unit has no elaboration routine. All subprogram specs are in this
category, as are subprogram bodies if access-before-elaboration checks
are being generated. Package bodies and specs may or may not have
<CODE>NE</CODE> set, depending on whether or not elaboration code is required.

<DT><CODE>PK</CODE>
<DD>
Unit is a package.

<DT><CODE>PU</CODE>
<DD>
<A NAME="IDX38"></A>
Unit has pragma <CODE>Pure</CODE>.

<DT><CODE>PR</CODE>
<DD>
<A NAME="IDX39"></A>
Unit has pragma <CODE>Preelaborate</CODE>.

<DT><CODE>RC</CODE>
<DD>
<A NAME="IDX40"></A>
Unit has pragma <CODE>Remote_Call_Interface</CODE>.

<DT><CODE>RT</CODE>
<DD>
<A NAME="IDX41"></A>
Unit has pragma <CODE>Remote_Types</CODE>.

<DT><CODE>SP</CODE>
<DD>
<A NAME="IDX42"></A>
Unit has pragma <CODE>Shared_Passive</CODE>.

<DT><CODE>SU</CODE>
<DD>
Unit is a subprogram.
</DL>

<P>
The attributes may appear in any order, separated by spaces.  The next
set of lines in the ALI file have the following form:

</P>

<PRE>
   W <VAR>unit-name</VAR> [<VAR>source-name</VAR> <VAR>lib-name</VAR> [E] [EA] [ED]]
</PRE>

<P>
<A NAME="IDX43"></A>
<A NAME="IDX44"></A>
One of these lines is present for each unit mentioned in an explicit
<CODE>with</CODE> clause in the current unit. <VAR>unit-name</VAR> is the unit name
in internal format. <VAR>source-name</VAR> is the file name of the file that
must be compiled to compile that unit (usually the file for the body,
except for packages that have no body).  <VAR>lib-name</VAR> is the file name
of the library information file that contains the results of compiling
the unit. The <CODE>E</CODE> and <CODE>EA</CODE> parameters are present if
pragma <CODE>Elaborate</CODE> or pragma <CODE>Elaborate_All</CODE>, respectively,
apply to this unit. <CODE>ED</CODE> is used to indicate that the compiler
has determined that a pragma <CODE>Elaborate_All</CODE> for this unit would be
desirable. For details on the use of the ED parameter see
See section <A HREF="gnat_ug.html#SEC84">Elaboration Order Handling in GNAT</A>.

</P>
<P>
Following the unit information is an optional series of lines that
indicate the usage of pragma <CODE>Linker_Options</CODE>. For each appearance of
pragma <CODE>Linker_Options</CODE> in any of the units for which unit lines are
present, a line of the form

</P>

<PRE>
   L <VAR>string</VAR>
</PRE>

<P>
appears. <VAR>string</VAR> is the string from the pragma enclosed in
quotes. Within the quotes, the following can occur:

<UL>

<LI>

7-bit graphic characters other than " or {
<LI>

"" (indicating a single " character)

<LI>

{hh} indicating a character whose code is hex hh
</UL>

<P>
<A NAME="IDX45"></A>
<A NAME="IDX46"></A>
For further details, see <CODE>Stringt.Write_String_Table_Entry</CODE> in the
file <TT>`stringt.ads'</TT>. Note that wide characters of the form {hhhh}
cannot be produced, because <CODE>pragma Linker_Option</CODE> accepts only
<CODE>String</CODE>, not <CODE>Wide_String</CODE>.

</P>
<P>
Finally, the rest of the ALI file contains a series of lines that
indicate the source files on which the compiled units depend. This is
used by the binder for consistency checking and looks like:

<PRE>
   D <VAR>source-name</VAR> <VAR>time-stamp</VAR> [<VAR>comments</VAR>]
</PRE>

<P>
where
<VAR>comments</VAR>, if present, must be separated from the time stamp by at
least one blank. Currently this field is unused.

</P>
<P>
Blank lines are ignored when the library information is read, and
separate sections of the file are separated by blank lines to help
readability. Extra blanks between fields are also ignored.

</P>


<H2><A NAME="SEC22" HREF="gnat_ug_toc.html#TOC22">Representation of Time Stamps</A></H2>

<P>
All compiled units are marked with a time stamp, which is derived from
the source file. The binder uses these time stamps to ensure consistency
of the set of units that constitutes a single program. Time stamps are
fourteen-character strings of the form <VAR>YYYYMMDDHHMMSS</VAR>.  The
fields have the following meaning:

</P>
<DL COMPACT>

<DT><CODE>YYYY</CODE>
<DD>
year (4 digits)
<DT><CODE>MM</CODE>
<DD>
month (2 digits 01-12)
<DT><CODE>DD</CODE>
<DD>
day (2 digits 01-31)
<DT><CODE>HH</CODE>
<DD>
hour (2 digits 00-23)
<DT><CODE>MM</CODE>
<DD>
minutes (2 digits 00-59)
<DT><CODE>SS</CODE>
<DD>
seconds (2 digits 00-59)
</DL>

<P>
Time stamps may be compared lexicographically (in other words, the order
of Ada comparison operations on strings) to determine which is later or
earlier. However, in normal mode, only equality comparisons have any
effect on the semantics of the library. Later/earlier comparisons are
used only for determining the most informative error messages to be
issued by the binder.

</P>
<P>
The time stamp is the actual stamp stored with the file without any
adjustment resulting from time zone comparisons. This avoids problems in
using libraries across networks with clients spread across multiple time
zones, but it means that the time stamp might differ from that displayed in a
directory listing. For example, in UNIX systems,
file time stamps are stored in Greenwich Mean Time (GMT), but the
<CODE>ls</CODE> command displays local times.

</P>


<H2><A NAME="SEC23" HREF="gnat_ug_toc.html#TOC23">Binding an Ada Program</A></H2>

<P>
When using languages such as C and C++, once the source files have been
compiled the only remaining step in building an executable program
is linking the object modules together.  This means that it is possible to
link an inconsistent version of a program, in which two units have
included different versions of the same header.

</P>
<P>
The rules of Ada do not permit such an inconsistent program to be built.
For example, if two clients have different versions of the same package,
it is illegal to build a program containing these two clients.
These rules are enforced by the GNAT binder, which also determines an
elaboration order consistent with the Ada rules.

</P>
<P>
The GNAT binder is run after all the object files for a program have
been created. It is given the name of the main program unit, and from
this it determines the set of units required by the program, by reading the
corresponding ALI files. It generates error messages if the program is
inconsistent or if no valid order of elaboration exists.

</P>
<P>
If no errors are detected, the binder produces a main program, in Ada by
default, that contains calls to the elaboration procedures of those
compilation unit that require them, followed by
a call to the main program. This Ada program is compiled to generate the
object file for the main program. The name of
the Ada file is <CODE>b~<VAR>xxx</VAR>.adb</CODE> (with the corresponding spec
<CODE>b~<VAR>xxx</VAR>.ads</CODE>) where <VAR>xxx</VAR> is the name of the
main program unit.

</P>
<P>
Finally, the linker is used to build the resulting executable program,
using the object from the main program from the bind step as well as the
object files for the Ada units of the program.

</P>


<H2><A NAME="SEC24" HREF="gnat_ug_toc.html#TOC24">Mixed Language Programming</A></H2>
<P>
<A NAME="IDX47"></A>

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC25">Interfacing to C</A>
<LI><A HREF="gnat_ug.html#SEC26">Calling Conventions</A>
</UL>



<H3><A NAME="SEC25" HREF="gnat_ug_toc.html#TOC25">Interfacing to C</A></H3>
<P>
There are two ways to
build a program that contains some Ada files and some other language
files depending on whether the main program is in Ada or not.
If the main program is in Ada, you should proceed as follows:

</P>

<OL>
<LI>

Compile the other language files to generate object files. For instance:

<PRE>
gcc -c file1.c
gcc -c file2.c
</PRE>

<LI>

Compile the Ada units to produce a set of object files and ALI
files. For instance:

<PRE>
gnatmake -c my_main.adb
</PRE>

<LI>

Run the Ada binder on the Ada main program. For instance:

<PRE>
gnatbind my_main
</PRE>

<LI>

Link the Ada main program, the Ada objects and the other language
objects. For instance:

<PRE>
gnatlink my_main.ali file1.o file2.o
</PRE>

</OL>

<P>
The three last steps can be grouped in a single command:

<PRE>
gnatmake my_main.adb -largs file1.o file2.o
</PRE>

<P>
<A NAME="IDX48"></A>
If the main program is in some language other than Ada, Then you may
have more than one entry point in the Ada subsystem. You must use a
special option of the binder to generate callable routines to initialize
and finalize the Ada units (see section <A HREF="gnat_ug.html#SEC58">Binding with Non-Ada Main Programs</A>).
Calls to the initialization and finalization routines must be inserted in
the main program, or some other appropriate point in the code.  The call to
initialize the Ada units must occur before the first Ada subprogram is
called, and the call to finalize the Ada units must occur after the last
Ada subprogram returns. You use the same procedure for building the
program as described previously.  In this case, however, the binder
only places the initialization and finalization subprograms into file
<TT>`b~<VAR>xxx</VAR>.adb'</TT> instead of the main program.
So, if the main program is not in Ada, you should proceed as follows:

</P>

<OL>
<LI>

Compile the other language files to generate object files. For instance:

<PRE>
gcc -c file1.c
gcc -c file2.c
</PRE>

<LI>

Compile the Ada units to produce a set of object files and ALI
files. For instance:

<PRE>
gnatmake -c entry_point1.adb
gnatmake -c entry_point2.adb
</PRE>

<LI>

Run the Ada binder on the Ada main program. For instance:

<PRE>
gnatbind -n entry_point1 entry_point2
</PRE>

<LI>

Link the Ada main program, the Ada objects and the other language
objects. You only need to give the last entry point here. For instance:

<PRE>
gnatlink entry_point2.ali file1.o file2.o
</PRE>

</OL>



<H3><A NAME="SEC26" HREF="gnat_ug_toc.html#TOC26">Calling Conventions</A></H3>
<P>
<A NAME="IDX49"></A>
<A NAME="IDX50"></A>
GNAT follows standard calling sequence conventions and will thus interface
to any other language that also follows these conventions. The following
Convention identifiers are recognized by GNAT:

</P>

<UL>
<LI>

<A NAME="IDX51"></A>
 <A NAME="IDX52"></A>
 <A NAME="IDX53"></A>
 
Ada. This indicates that the standard Ada calling sequence will be
used and all Ada data items may be passed without any limitations in the
case where GNAT is used to generate both the caller and callee. It is also
possible to mix GNAT generated code and code generated by another Ada
compiler. In this case, the data types should be restricted to simple
cases, including primitive types. Whether complex data types can be passed
depends on the situation. Probably it is safe to pass simple arrays, such
as arrays of integers or floats. Records may or may not work, depending
on whether both compilers lay them out identically. Complex structures
involving variant records, access parameters, tasks, or protected types,
are unlikely to be able to be passed.

Note that in the case of GNAT running
on a platform that supports DEC Ada 83, a higher degree of compatibility
can be guaranteed, and in particular records are layed out in an identical
manner in the two compilers. Note also that if output from two different
compilers is mixed, the program is responsible for dealing with elaboration
issues. Probably the safest approach is to write the main program in the
version of Ada other than GNAT, so that it takes care of its own elaboration
requirements, and then call the GNAT-generated adainit procedure to ensure
elaboration of the GNAT components. Consult the documentation of the other
Ada compiler for further details on elaboration.

However, it is not possible to mix the tasking runtime of GNAT and
DEC Ada 83, All the tasking operations must either be entirely within
GNAT compiled sections of the program, or entirely within DEC Ada 83
compiled sections of the program.

<A NAME="IDX54"></A>
<A NAME="IDX55"></A>
<LI>

Asm. Equivalent to Ada.

<A NAME="IDX56"></A>
<LI>

Assembler. Equivalent to Ada.

<A NAME="IDX57"></A>
<A NAME="IDX58"></A>
<A NAME="IDX59"></A>
<LI>

COBOL. Data will be passed according to the conventions described
in section B.4 of the Ada 95 Reference Manual.

<A NAME="IDX60"></A>
<A NAME="IDX61"></A>
<A NAME="IDX62"></A>
<LI>

C. Data will be passed according to the conventions described
in section B.3 of the Ada 95 Reference Manual.

<A NAME="IDX63"></A>
<A NAME="IDX64"></A>
<A NAME="IDX65"></A>
<LI>

CPP. This stands for C++. For most purposes this is identical to C.
See the separate description of the specialized GNAT pragmas relating to
C++ interfacing for further details.

<A NAME="IDX66"></A>
<A NAME="IDX67"></A>
<A NAME="IDX68"></A>
<LI>

Fortran. Data will be passed according to the conventions described
in section B.5 of the Ada 95 Reference Manual.

<LI>

Intrinsic. This defines an intrinsic operation, as defined in the Ada 95
Reference Manual. Normally this is not used in application programs. The
one exception is that GNAT permits the use of Intrinsic for defining shift
operations on user defined (signed and unsigned) integer types.

<A NAME="IDX69"></A>
<A NAME="IDX70"></A>
<LI>

Stdcall. This is relevant only to NT/Win95 implementations of GNAT,
and specifies that the Stdcall calling sequence will be used, as defined
by the NT API.

<A NAME="IDX71"></A>
<A NAME="IDX72"></A>
<LI>

Stubbed. This is a special convention that indicates that the compiler
should provide a stub body that raises Program_Error.
</UL>



<H2><A NAME="SEC27" HREF="gnat_ug_toc.html#TOC27">Building mixed Ada &#38; C++ programs</A></H2>

<P>
Building a mixed application containing both Ada and C++ code may be a
challenge for the unaware programmer. As a matter of fact, this
interfacing has not been standardized in the Ada 95 reference manual due
to the immaturity and lack of standard of C++ at the time. This
section gives a few hints that should make this task easier. In
particular the first section addresses the differences with
interfacing with C. The second section looks into the delicate problem
of linking the complete application from its Ada and C++ parts. The last
section give some hints on how the GNAT runtime can be adapted in order
to allow inter-language dispatching with a new C++ compiler.

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC28">Interfacing to C++</A>
<LI><A HREF="gnat_ug.html#SEC29">Linking a mixed C++ &#38; Ada program</A>
<LI><A HREF="gnat_ug.html#SEC30">Adapting the runtime to a new C++ compiler</A>
</UL>



<H3><A NAME="SEC28" HREF="gnat_ug_toc.html#TOC28">Interfacing to C++</A></H3>

<P>
GNAT supports interfacing with C++ compilers generating code that is
compatible with the standard Application Binary Interface of the given
platform.

</P>
<P>
Interfacing can be done at 3 levels: simple data, subprograms and
classes. In the first 2 cases, GNAT offer a specific <VAR>Convention
CPP</VAR> that behaves exactly like <VAR>Convention C</VAR>. Usually C++ mangle
names of subprograms and currently GNAT does not provide any help to
solve the demangling problem. This problem can be addressed in 2 ways:

<UL>
<LI>

by modifying the C++ code in order to force a C convention using
the <VAR>extern "C"</VAR> syntax.

<LI>

by figuring out the mangled name and use it as the Link_Name argument of
the pragma import.
</UL>

<P>
Interfacing at the class level can be achieved by using the GNAT specific
pragmas such as <CODE>CPP_Class</CODE> and <CODE> CPP_Virtual</CODE>. See the GNAT
Reference Manual for additional information.

</P>


<H3><A NAME="SEC29" HREF="gnat_ug_toc.html#TOC29">Linking a mixed C++ &#38; Ada program</A></H3>

<P>
Usually the linker of the C++ development system must be used to link
mixed applications because most C++ systems will resolve elaboration
issues (such as calling constructors on global class instances)
transparently during the link phase. GNAT has been adapted to ease the
use of a foreign linker for the last phase. Three cases can be
considered:

<OL>

<LI>

Using GNAT and G++ (GNU C++ compiler) from the same GCC
installation. The c++ linker can simply be called by using the c++
specific driver called <CODE>c++</CODE>. Note that this setup is not
very common because it may request recompiling the whole GCC
tree from sources and it does not allow to upgrade easily to a new
version of one compiler for one of the two languages without taking the
risk of destabilizing the other.


<PRE>
$ c++ -c file1.C
$ c++ -c file2.C
$ gnatmake ada_unit -largs file1.o file2.o --LINK=c++
</PRE>

<LI>

Using GNAT and G++ from 2 different GCC installations.  If both
compilers are on the PATH, the same method can be used. It is important
to be aware that environment variables such as C_INCLUDE_PATH or
GCC_EXEC_PREFIX will affect both compilers at the same time and thus may
make one of the 2 compilers operate improperly if they are set for the
other. In particular it is important that the link command has access to
the proper gcc library 'libgcc.a', that is to say the one that is part
of the C++ compiler installation. The implicit link command as suggested
in the gnatmake command from the former example can be replaced by an
explicit link command with full verbosity in order to verify which
library is used:

<PRE>
$ gnatbind ada_unit
$ gnatlink -v -v ada_unit file1.o file2.o --LINK=c++
</PRE>

If there is a problem due to interfering environment variables, it can be
workaround by using an intermediate script:


<PRE>
$ gnatlink -v -v ada_unit file1.o file2.o --LINK=./my_script
$ cat ./my_script
#!/bin/sh
unset C_INCLUDE_PATH
unset GCC_EXEC_PREFIX
c++ $*
</PRE>

<LI>

Using a non GNU C++ compiler.  The same set of command as previously
described can be used to insure that the c++ linker is
used. Nonetheless, the Ada code may implicitly depend on the gcc
library. The latter can be located thanks to gnatls: it is to be found
on the last directory of the object path. It must then be explicitly
mentioned in the link command :

<PRE>
$ gnatls -v
$ Gdir=&#60;the last directory on the object path&#62;
$ gnatlink ada_unit file1.o file2.o -L$Gdir -lgcc --LINK=&#60;cpp_linker&#62;
</PRE>

</OL>



<H3><A NAME="SEC30" HREF="gnat_ug_toc.html#TOC30">Adapting the runtime to a new C++ compiler</A></H3>
<P>
GNAT offers the capability to derive Ada 95 tagged types directly from
preexisting C++ classes and . See "Interfacing with C++" in the GNAT
reference manual. The mechanism used by GNAT for achieving such a goal
has been made user configurable through a GNAT library unit
<CODE>Interfaces.CPP</CODE>. The default version of this file is adapted to
the GNU c++ compiler. Internal knowledge of the virtual
table layout used by the new C++ compiler is needed to configure
properly this unit. The Interface of this unit is known by the compiler
and cannot be changed except for the value of the constants defining the
characteristics of the virtual table: CPP_DT_Prologue_Size, CPP_DT_Entry_Size,
CPP_TSD_Prologue_Size, CPP_TSD_Entry_Size. Read comments in the source
of this unit for more details.

</P>



<H2><A NAME="SEC31" HREF="gnat_ug_toc.html#TOC31">Comparison between GNAT and C/C++ Compilation Models</A></H2>

<P>
The GNAT model of compilation is close to the C and C++ models. You can
think of Ada specs as corresponding to header files in C. As in C, you
don't need to compile specs; they are compiled when they are used. The
Ada <CODE>with</CODE> is similar in effect to the <CODE>#include</CODE> of a C
header.

</P>
<P>
One notable difference is that, in Ada, you may compile specs separately
to check them for semantic and syntactic accuracy. This is not always
possible with C headers because they are fragments of programs that have
less specific syntactic or semantic rules.

</P>
<P>
The other major difference is the requirement for running the binder,
which performs two important functions. First, it checks for
consistency. In C or C++, the only defense against assembling
inconsistent programs lies outside the compiler, in a makefile, for
example. The binder satisfies the Ada requirement that it be impossible
to construct an inconsistent program when the compiler is used in normal
mode.

</P>
<P>
<A NAME="IDX73"></A>
The other important function of the binder is to deal with elaboration
issues. There are also elaboration issues in C++ that are handled
automatically.  This automatic handling has the advantage of being
simpler to use, but the C++ programmer has no control over elaboration.
Where <CODE>gnatbind</CODE> might complain there was no valid order of
elaboration, a C++ compiler would simply construct a program that
malfunctioned at run time.

</P>


<H2><A NAME="SEC32" HREF="gnat_ug_toc.html#TOC32">Comparison between GNAT and Conventional Ada Library Models</A></H2>

<P>
This section is intended to be useful to Ada programmers who have
previously used an Ada compiler implementing the traditional Ada library
model, as described in the Ada 95 Language Reference Manual. If you
have not used such a system, please go on to the next section.

</P>
<P>
<A NAME="IDX74"></A>
In GNAT, there is no <STRONG>library</STRONG> in the normal sense. Instead, the set of
source files themselves acts as the library. Compiling Ada programs does
not generate any centralized information, but rather an object file and
a ALI file, which are of interest only to the binder and linker.
In a traditional system, the compiler reads information not only from
the source file being compiled, but also from the centralized library.
This means that the effect of a compilation depends on what has been
previously compiled. In particular:

</P>

<UL>
<LI>

When a unit is <CODE>with</CODE>'ed, the unit seen by the compiler corresponds
to the version of the unit most recently compiled into the library.

<LI>

Inlining is effective only if the necessary body has already been
compiled into the library.

<LI>

Compiling a unit may obsolete other units in the library.
</UL>

<P>
In GNAT, compiling one unit never affects the compilation of any other
units because the compiler reads only source files. Only changes to source
files can affect the results of a compilation. In particular:

</P>

<UL>
<LI>

When a unit is <CODE>with</CODE>'ed, the unit seen by the compiler corresponds
to the source version of the unit that is currently accessible to the
compiler.

<LI>

<A NAME="IDX75"></A>
Inlining requires the appropriate source files for the package or
subprogram bodies to be available to the compiler. Inlining is always
effective, independent of the order in which units are complied.

<LI>

Compiling a unit never affects any other compilations. The editing of
sources may cause previous compilations to be out of date if they
depended on the source file being modified.
</UL>

<P>
The most important result of these differences is that order of compilation
is never significant in GNAT. There is no situation in which one is
required to do one compilation before another. What shows up as order of
compilation requirements in the traditional Ada library becomes, in
GNAT, simple source dependencies; in other words, there is only a set
of rules saying what source files must be present when a file is
compiled.

</P>


<H1><A NAME="SEC33" HREF="gnat_ug_toc.html#TOC33">Compiling Using <CODE>gcc</CODE></A></H1>

<P>
This chapter discusses how to compile Ada programs using the <CODE>gcc</CODE>
command. It also describes the set of switches
that can be used to control the behavior of the compiler.

<UL>
<LI><A HREF="gnat_ug.html#SEC34">Compiling Programs</A>
<LI><A HREF="gnat_ug.html#SEC35">Switches for gcc</A>
<LI><A HREF="gnat_ug.html#SEC49">Search Paths and the Run-Time Library (RTL)</A>
<LI><A HREF="gnat_ug.html#SEC50">Order of Compilation Issues</A>
<LI><A HREF="gnat_ug.html#SEC51">Examples</A>
</UL>



<H2><A NAME="SEC34" HREF="gnat_ug_toc.html#TOC34">Compiling Programs</A></H2>

<P>
The first step in creating an executable program is to compile the units
of the program using the <CODE>gcc</CODE> command. You must compile the
following files:

</P>

<UL>
<LI>

the body file (<TT>`.adb'</TT>) for a library level subprogram or generic
subprogram

<LI>

the spec file (<TT>`.ads'</TT>) for a library level package or generic
package that has no body

<LI>

the body file (<TT>`.adb'</TT>) for a library level package
or generic package that has a body

</UL>

<P>
You need <EM>not</EM> compile the following files

</P>

<UL>

<LI>

the spec of a library unit which has a body

<LI>

subunits
</UL>

<P>
because they are compiled as part of compiling related units. GNAT
package specs
when the corresponding body is compiled, and subunits when the parent is
compiled.
<A NAME="IDX76"></A>
If you attempt to compile any of these files, you will get one of the
following error messages (where fff is the name of the file you compiled):

</P>

<PRE>
   No code generated for file <VAR>fff</VAR> (<VAR>package spec</VAR>)
   No code generated for file <VAR>fff</VAR> (<VAR>subunit</VAR>)
</PRE>

<P>
The basic command for compiling a file containing an Ada unit is

</P>

<PRE>
   $ gcc -c [<VAR>switches</VAR>] <TT>`file name'</TT>
</PRE>

<P>
where <VAR>file name</VAR> is the name of the Ada file (usually
having an extension
<TT>`.ads'</TT> for a spec or <TT>`.adb'</TT> for a body).
You specify the
<CODE>-c</CODE> switch to tell <CODE>gcc</CODE> to compile, but not link, the file.
The result of a successful compilation is an object file, which has the
same name as the source file but an extension of <TT>`.o'</TT> and an Ada
Library Information (ALI) file, which also has the same name as the
source file, but with <TT>`.ali'</TT> as the extension. GNAT creates these
two output files in the current directory, but you may specify a source
file in any directory using an absolute or relative path specification
containing the directory information.

</P>
<P>
<A NAME="IDX77"></A>
<CODE>gcc</CODE> is actually a driver program that looks at the extensions of
the file arguments and loads the appropriate compiler. For example, the
GNU C compiler is <TT>`cc1'</TT>, and the Ada compiler is <TT>`gnat1'</TT>.
These programs are in directories known to the driver program (in some
configurations via environment variables you set), but need not be in
your path.  The <CODE>gcc</CODE> driver also calls the assembler and any other
utilities needed to complete the generation of the required object
files.

</P>
<P>
It is possible to supply several file names on the same <CODE>gcc</CODE>
command. This causes <CODE>gcc</CODE> to call the appropriate compiler for
each file. For example, the following command lists three separate
files to be compiled:

</P>

<PRE>
   $ gcc -c x.adb y.adb z.c
</PRE>

<P>
calls <CODE>gnat1</CODE> (the Ada compiler) twice to compile <TT>`x.adb'</TT> and
<TT>`y.adb'</TT>, and <CODE>cc1</CODE> (the C compiler) once to compile <TT>`z.c'</TT>.
The compiler generates three object files <TT>`x.o'</TT>, <TT>`y.o'</TT> and
<TT>`z.o'</TT> and the two ALI files <TT>`x.ali'</TT> and <TT>`y.ali'</TT> from the
Ada compilations. Any switches apply to all the files listed,
except for
<CODE>-gnat<VAR>x</VAR></CODE> switches, which apply only to Ada compilations.

</P>


<H2><A NAME="SEC35" HREF="gnat_ug_toc.html#TOC35">Switches for <CODE>gcc</CODE></A></H2>

<P>
The <CODE>gcc</CODE> command accepts numerous switches to control the
compilation process. These switches are fully described in this section.

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC36">Output and Error Message Control</A>
<LI><A HREF="gnat_ug.html#SEC37">Debugging and Assertion Control</A>
<LI><A HREF="gnat_ug.html#SEC39">Run-time Checks</A>
<LI><A HREF="gnat_ug.html#SEC38">Style Checking</A>
<LI><A HREF="gnat_ug.html#SEC40">Using gcc for Syntax Checking</A>
<LI><A HREF="gnat_ug.html#SEC41">Using gcc for Semantic Checking</A>
<LI><A HREF="gnat_ug.html#SEC42">Compiling Ada 83 Programs</A>
<LI><A HREF="gnat_ug.html#SEC43">Reference Manual Style Checking</A>
<LI><A HREF="gnat_ug.html#SEC44">Character Set Control</A>
<LI><A HREF="gnat_ug.html#SEC45">File Naming Control</A>
<LI><A HREF="gnat_ug.html#SEC46">Subprogram Inlining Control</A>
<LI><A HREF="gnat_ug.html#SEC47">Auxiliary Output Control</A>
<LI><A HREF="gnat_ug.html#SEC48">Debugging Control</A>
</UL>

<DL COMPACT>

<DT><CODE>-b <VAR>target</VAR></CODE>
<DD>
<A NAME="IDX78"></A>
 
Compile your program to run on <VAR>target</VAR>, which is the name of a
system configuration.  You must have a GNAT cross-compiler built if
<VAR>target</VAR> is not the same as your host system.

<DT><CODE>-B<VAR>dir</VAR></CODE>
<DD>
<A NAME="IDX79"></A>
Load compiler executables (for example, <CODE>gnat1</CODE>, the Ada compiler)
from <VAR>dir</VAR> instead of the default location. Only use this switch
when multiple versions of the GNAT compiler are available. See the
<CODE>gcc</CODE> manual page for further details.  You would normally use the
<CODE>-b</CODE> or <CODE>-V</CODE> switch instead.

<DT><CODE>-c</CODE>
<DD>
<A NAME="IDX80"></A>
Compile. Always use this switch when compiling Ada programs.

Note that you may not use <CODE>gcc</CODE> without a <CODE>-c</CODE> switch to
compile and link in one step. This is because the binder must be run,
and currently <CODE>gcc</CODE> cannot be used to run the GNAT binder.

<DT><CODE>-g</CODE>
<DD>
<A NAME="IDX81"></A>
Generate debugging information. This information is stored in the object
file and copied from there to the final executable file by the linker,
where it can be read by the debugger. You must use the <CODE>-g</CODE> switch
if you plan on using the debugger.

<DT><CODE>-I<VAR>dir</VAR></CODE>
<DD>
<A NAME="IDX82"></A>
<A NAME="IDX83"></A>
Direct GNAT to search the <VAR>dir</VAR> directory for source files needed by
the current compilation (see section <A HREF="gnat_ug.html#SEC49">Search Paths and the Run-Time Library (RTL)</A>).

<DT><CODE>-I-</CODE>
<DD>
<A NAME="IDX84"></A>
<A NAME="IDX85"></A>
Do not look for source files in the directory containing the source
file named in the command line
(see section <A HREF="gnat_ug.html#SEC49">Search Paths and the Run-Time Library (RTL)</A>).

<DT><CODE>-o <VAR>file</VAR></CODE>
<DD>
<A NAME="IDX86"></A>
This switch is used in <CODE>gcc</CODE> to redirect the generated object file
and its associated ALI file. Beware of this switch with GNAT, because it may
cause the object file and ALI file to have different names which in turn
may confuse the binder and the linker.

<DT><CODE>-O[<VAR>n</VAR>]</CODE>
<DD>
<A NAME="IDX87"></A>
<VAR>n</VAR> controls the optimization level.

<DL COMPACT>

<DT>n = 0
<DD>
No optimization, the default setting if no <CODE>-O</CODE> appears

<DT>n = 1
<DD>
Normal optimization, the default if you specify <CODE>-O</CODE> without
an operand.

<DT>n = 2
<DD>
Extensive optimization

<DT>n = 3
<DD>
Extensive optimization with automatic inlining. This applies only to
inlining within a unit. For details on control of inter-unit inlining
see See section <A HREF="gnat_ug.html#SEC46">Subprogram Inlining Control</A>.
</DL>

<DT><CODE>-S</CODE>
<DD>
<A NAME="IDX88"></A>
Used in place of <CODE>-c</CODE> to
cause the assembler source file to be
generated, using <TT>`.s'</TT> as the extension,
instead of the object file.
This may be useful if you need to examine the generated assembly code.

<DT><CODE>-v</CODE>
<DD>
<A NAME="IDX89"></A>
Show commands generated by the <CODE>gcc</CODE> driver. Normally used only for
debugging purposes or if you need to be sure what version of the
compiler you are executing.

<DT><CODE>-V <VAR>ver</VAR></CODE>
<DD>
<A NAME="IDX90"></A>
Execute <VAR>ver</VAR> version of the compiler.  This is the <CODE>gcc</CODE>
version, not the GNAT version.

<DT><CODE>-Wuninitialized</CODE>
<DD>
<A NAME="IDX91"></A>
Generate warnings for uninitialized variables. You must also specify the
<CODE>-O</CODE> switch (in other words, This switch works only if
optimization is turned on).

<DT><CODE>-gnata</CODE>
<DD>
Assertions enabled. <CODE>Pragma Assert</CODE> and <CODE>pragma Debug</CODE> to be
activated.

<DT><CODE>-gnatb</CODE>
<DD>
Generate brief messages to <CODE>stderr</CODE> even if verbose mode set.

<DT><CODE>-gnatc</CODE>
<DD>
Check syntax and semantics only (no code generation attempted).

<DT><CODE>-gnatD</CODE>
<DD>
Output expanded source files for source level debugging.

<DT><CODE>-gnate</CODE>
<DD>
Force error message generation (for use when compiler crashes).

<DT><CODE>-gnatE</CODE>
<DD>
Full dynamic elaboration checks.

<DT><CODE>-gnatf</CODE>
<DD>
Full errors. Multiple errors per line, all undefined references.

<DT><CODE>-gnatg</CODE>
<DD>
GNAT style checks enabled.

<DT><CODE>-gnatG</CODE>
<DD>
List generated expanded code in source form.

<DT><CODE>-gnati<VAR>c</VAR></CODE>
<DD>
Identifier character set
(<VAR>c</VAR>=1/2/3/4/8/p/f/n/w).

<DT><CODE>-gnath</CODE>
<DD>
Output usage information. The output is written to <CODE>stdout</CODE>.

<DT><CODE>-gnatk<VAR>n</VAR></CODE>
<DD>
Limit file names to <VAR>n</VAR> (1-999) characters (<CODE>k</CODE> = krunch).

<DT><CODE>-gnatl</CODE>
<DD>
Output full source listing with embedded error messages.

<DT><CODE>-gnatm<VAR>n</VAR></CODE>
<DD>
Limit number of detected errors to <VAR>n</VAR> (1-999).

<DT><CODE>-gnatn</CODE>
<DD>
Activate inlining across unit boundaries for subprograms for which
pragma <CODE>inline</CODE> is specified.

<DT><CODE>-gnatN</CODE>
<DD>
Activate inlining across unit boundaries for all subprograms (not just
those for which pragma <CODE>inline</CODE> is specified. This is equivalent
to using <CODE>-gnatn</CODE> and adding a pragma <CODE>inline</CODE> for every
subprogram in the program.

<DT><CODE>-fno-inline</CODE>
<DD>
Suppresses all inlining, even if other optimization or inlining switches
are set.

<DT><CODE>-gnato</CODE>
<DD>
Enable other checks, not normally enabled by default, including numeric
overflow checking, and access before elaboration checks.

<DT><CODE>-gnatp</CODE>
<DD>
Suppress all checks.

<DT><CODE>-gnatq</CODE>
<DD>
Don't quit; try semantics, even if parse errors.

<DT><CODE>-gnatP</CODE>
<DD>
Enable polling. This is required on some systems (notably Windows NT) to
obtain asynchronous abort and asynchronous transfer of control capability.
See the description of pragma Polling in the GNAT Reference Manual for
full details.

<DT><CODE>-gnatR</CODE>
<DD>
Output representation information for declared array and record types.

<DT><CODE>-gnats</CODE>
<DD>
Syntax check only.

<DT><CODE>-gnatt</CODE>
<DD>
Tree output file to be generated.

<DT><CODE>-gnatu</CODE>
<DD>
List units for this compilation.

<DT><CODE>-gnatU</CODE>
<DD>
Tag all error messages with the unique string "error:"

<DT><CODE>-gnatv</CODE>
<DD>
Verbose mode. Full error output with source lines to <CODE>stdout</CODE>.

<DT><CODE>-gnatw<VAR>m</VAR></CODE>
<DD>
Warning mode
(<VAR>m</VAR>=<CODE>s,e,l</CODE> for suppress, treat as error, elaboration
warnings).

<DT><CODE>-gnatW<VAR>e</VAR></CODE>
<DD>
Wide character encoding method
(<VAR>e</VAR>=n/h/u/s/e/8).

<DT><CODE>-gnatx</CODE>
<DD>
Suppress generation of cross-reference information.

<DT><CODE>-gnatw<VAR>m</VAR></CODE>
<DD>
Warning mode
<DT><CODE>-gnaty</CODE>
<DD>
Enable built-in style checks. See separate section describing this feature.

<DT><CODE>-gnatz<VAR>m</VAR></CODE>
<DD>
Distribution stub generation and compilation
(<VAR>m</VAR>=r/c for receiver/caller stubs).

<DT><CODE>-gnat83</CODE>
<DD>
Enforce Ada 83 restrictions.

<DT><CODE>-gnat95</CODE>
<DD>
Standard Ada 95 mode
</DL>

<P>
You may combine a sequence of GNAT switches into a single switch. For
example, the combined switch

</P>
<P>
<A NAME="IDX92"></A>

<PRE>
   -gnatcfi3
</PRE>

<P>
is equivalent to specifying the following sequence of switches:

</P>

<PRE>
   -gnatc -gnatf -gnati3
</PRE>



<H3><A NAME="SEC36" HREF="gnat_ug_toc.html#TOC36">Output and Error Message Control</A></H3>
<P>
<A NAME="IDX93"></A>

</P>
<P>
The standard default format for error messages is called "brief format."
Brief format messages are written to <CODE>stdout</CODE> (the standard output
file) and have the following form:

</P>

<PRE>
   e.adb:3:04: Incorrect spelling of keyword "function"
   e.adb:4:20: ";" should be "is"
</PRE>

<P>
The first integer after the file name is the line number in the file,
and the second integer is the column number within the line.
<CODE>emacs</CODE> can parse the error messages
and point to the referenced character.
The following switches provide control over the error message
format:

</P>
<DL COMPACT>

<DT><CODE>-gnatv</CODE>
<DD>
<A NAME="IDX94"></A>
<A NAME="IDX95"></A>
The v stands for verbose.
The effect of this setting is to write long-format error
messages to <CODE>stdout</CODE>. The same program compiled with the
<CODE>-gnatv</CODE> switch would generate:


<PRE>
   3. funcion X (Q : Integer)
      |
   &#62;&#62;&#62; Incorrect spelling of keyword "function"
   4. return Integer;
                    |
   &#62;&#62;&#62; ";" should be "is"
</PRE>

The vertical bar indicates the location of the error, and the <SAMP>`&#62;&#62;&#62;'</SAMP>
prefix can be used to search for error messages. When this switch is
used the only source lines output are those with errors.

<DT><CODE>-gnatl</CODE>
<DD>
<A NAME="IDX96"></A>
The <CODE>l</CODE> stands for list.
This switch causes a full listing of
the file to be generated. The output might look as follows:


<PRE>
    1. procedure E is
    2.    V : Integer;
    3.    funcion X (Q : Integer)
          |
       &#62;&#62;&#62; Incorrect spelling of keyword "function"
    4.     return Integer;
                         |
       &#62;&#62;&#62; ";" should be "is"
    5.    begin
    6.       return Q + Q;
    7.    end;
    8. begin
    9.    V := X + X;
   10.end E;
</PRE>

When you specify the <CODE>-gnatv</CODE> or <CODE>-gnatl</CODE> switches and
standard output is redirected, a brief summary is written to
<CODE>stderr</CODE> (standard error) giving the number of error messages and
warning messages generated.

<DT><CODE>-gnatU</CODE>
<DD>
<A NAME="IDX97"></A>
This switch forces all error messages to be preceded by the unique
string "error:". This means that error messages take a few more
characters in space, but allows easy searching for and identification
of error messages.

<DT><CODE>-gnatb</CODE>
<DD>
<A NAME="IDX98"></A>
The <CODE>b</CODE> stands for brief.
This switch causes GNAT to generate the
brief format error messages to <CODE>stdout</CODE> as well as the verbose
format message or full listing.

<DT><CODE>-gnatm<VAR>n</VAR></CODE>
<DD>
<A NAME="IDX99"></A>
The <CODE>m</CODE> stands for maximum.
<VAR>n</VAR> is a decimal integer in the
range of 1 to 999 and limits the number of error messages to be
generated. For example, using <CODE>-gnatm2</CODE> might yield


<PRE>
   e.adb:3:04: Incorrect spelling of keyword "function"
   e.adb:5:35: missing ".."
   fatal error: maximum errors reached
   compilation abandoned
</PRE>

<DT><CODE>-gnatf</CODE>
<DD>
<A NAME="IDX100"></A>
<A NAME="IDX101"></A>
The <CODE>f</CODE> stands for full.
Normally, the compiler suppresses error messages that are likely to be
redundant. This switch causes all error
messages to be generated. In particular, in the case of
references to undefined variables. If a given variable is referenced
several times, the normal format of messages is


<PRE>
   e.adb:7:07: "V" is undefined (more references follow)
</PRE>

where the parenthetical comment warns that there are additional
references to the variable <CODE>V</CODE>. Compiling the same program with the
<CODE>-gnatf</CODE> switch yields


<PRE>
   e.adb:7:07: "V" is undefined
   e.adb:8:07: "V" is undefined
   e.adb:8:12: "V" is undefined
   e.adb:8:16: "V" is undefined
   e.adb:9:07: "V" is undefined
   e.adb:9:12: "V" is undefined
</PRE>

<DT><CODE>-gnatq</CODE>
<DD>
<A NAME="IDX102"></A>
The <CODE>q</CODE> stands for quit (really "don't quit").
In normal operation mode, the compiler first parses the program and
determines if there are any syntax errors. If there are, appropriate
error messages are generated and compilation is immediately terminated.
This switch tells
GNAT to continue with semantic analysis even if syntax errors have been
found.  This may enable the detection of more errors in a single run. On
the other hand, the semantic analyzer is more likely to encounter some
internal fatal error when given a syntactically invalid tree.

<DT><CODE>-gnate</CODE>
<DD>
<A NAME="IDX103"></A>
Normally, the compiler saves up error messages and generates them at the
end of compilation in proper sequence.  This switch
 (the <SAMP>`e'</SAMP> stands for error)
causes error messages to be generated as soon as they are
detected. The use of <CODE>-gnate</CODE> may cause error messages to be
generated out of sequence and also disconnects a number of useful
error message processing circuits. This switch should be used only
in error situations where the compiler terminates with no output
at all, or goes into an infinite loop. In such cases, the
<CODE>-gnate</CODE> switch may be used to see if any error situations
were detected before the compiler crash (see section <A HREF="gnat_ug.html#SEC157">GNAT Abnormal Termination</A>).
</DL>

<P>
In addition to error messages, which correspond to illegalities as defined
in the Ada 95 Reference Manual, the compiler detects two kinds of warning
situations.

</P>
<P>
<A NAME="IDX104"></A>
First, the compiler considers some constructs suspicious and generates a
warning message to alert you to a possible error. Second, if the
compiler detects a situation that is sure to raise an exception at
run time, it generates a warning message. The following shows an example
of warning messages:

</P>

<PRE>
   e.adb:4:24: warning: creation of object may raise Storage_Error
   e.adb:10:17: warning: static value out of range
   e.adb:10:17: warning: "Constraint_Error" will be raised at run time
</PRE>

<P>
GNAT considers a large number of situations as appropriate
for the generation of warning messages. As always, warnings are not
definite indications of errors. For example, if you do an out-of-range
assignment with the deliberate intention of raising a
<CODE>Constraint_Error</CODE> exception, then the warning that may be
issued does not indicate an error. Some of the situations for which GNAT
issues warnings (at least some of the time) are:

</P>

<UL>
<LI>

Possible infinitely recursive calls

<LI>

Out-of-range values being assigned

<LI>

Possible order of elaboration problems

<LI>

Unreachable code

<LI>

Variables that are never assigned a value

<LI>

Variables that are referenced before being initialized

<LI>

Task entries with no corresponding Accept statement

<LI>

Duplicate Accepts for the same task entry in a select

<LI>

Objects that take too much storage

<LI>

Unchecked conversion between types of differing sizes

<LI>

Missing return statements along some execution paths in a function

<LI>

Incorrect pragmas

<LI>

Incorrect external names

<LI>

Allocation from empty storage pool

<LI>

Potentially blocking operations in protected types

<LI>

Suspicious parenthesization of expressions

<LI>

Mismatching bounds in an aggregate

<LI>

Attempt to return local value by reference

<LI>

Unrecognized pragmas

<LI>

Premature instantiation of a generic body

<LI>

Attempt to pack aliased components

<LI>

Out of bounds array subscripts

<LI>

Wrong length on string assignment
</UL>

<P>
Four switches are available to control the handling of warning messages:

</P>
<DL COMPACT>

<DT><CODE>-gnatwe (treat warnings as errors)</CODE>
<DD>
<A NAME="IDX105"></A>
This switch causes warning messages to be treated as errors.
The warning string still appears, but the warning messages are counted
as errors, and prevent the generation of an object file.

<DT><CODE>-gnatws (suppress warnings)</CODE>
<DD>
<A NAME="IDX106"></A>
This switch completely suppresses the
output of all warning messages.

<DT><CODE>-gnatwl (warn on elaboration order errors)</CODE>
<DD>
<A NAME="IDX107"></A>
This switch causes the generation
of additional warning messages relating to elaboration issues. See the
separate chapter on elaboration order handling for full details of the
use of this switch.

<DT><CODE>-gnatwu (warn on unused entities)</CODE>
<DD>
<A NAME="IDX108"></A>
This switch causes warning messages to be generated for entities that
are defined but not referenced, and for units that are <CODE>with</CODE>'ed
and not
referenced. In the case of packages, a warning is also generated if
no entities in the package are referenced. This means that if the package
is referenced but the only references are in <CODE>use</CODE>
clauses or <CODE>renames</CODE>
declarations, a warning is still generated. A warning is also generated
for a generic package that is <CODE>with</CODE>'ed but never instantiated.

<DT><CODE>-gnatR</CODE>
<DD>
<A NAME="IDX109"></A>
Use of the switch <CODE>-gnatR</CODE> causes the compiler to output a listing
showing representation information for declared array and record types,
including record representation clauses.

<DT><CODE>-gnatx</CODE>
<DD>
<A NAME="IDX110"></A>
Normally the compiler generates full cross-referencing information in
the <TT>`ALI'</TT> file. This information is used by a number of tools,
including <CODE>gnatfind</CODE> and <CODE>gnatxref</CODE>. The -gnatx switch
suppresses this information. This saves some space and may slightly
speed up compilation, but means that these tools cannot be used.
</DL>



<H3><A NAME="SEC37" HREF="gnat_ug_toc.html#TOC37">Debugging and Assertion Control</A></H3>

<DL COMPACT>

<DT><CODE>-gnata</CODE>
<DD>
<A NAME="IDX111"></A>
<A NAME="IDX112"></A>
<A NAME="IDX113"></A>
<A NAME="IDX114"></A>

The pragmas <CODE>Assert</CODE> and <CODE>Debug</CODE> normally have no effect and
are ignored. This switch, where <SAMP>`a'</SAMP> stands for assert, causes
<CODE>Assert</CODE> and <CODE>Debug</CODE> pragmas to be activated.

The pragmas have the form:


<PRE>
   <B>pragma</B> Assert (<VAR>Boolean-expression</VAR> [, <VAR>static-string-expression</VAR>])
   <B>pragma</B> Debug (<VAR>procedure call</VAR>)
</PRE>

The <CODE>Assert</CODE> pragma causes <VAR>Boolean-expression</VAR> to be tested.
If the result is <CODE>True</CODE>, the pragma has no effect (other than
possible side effects from evaluating the expression). If the result is
<CODE>False</CODE>, the exception <CODE>Assert_Error</CODE> declared in the package
<CODE>System.Assertions</CODE> is
raised (passing <VAR>static-string-expression</VAR>, if present, as the
message associated with the exception). If no string expression is
given the default is a string giving the file name and line number
of the pragma.

The <CODE>Debug</CODE> pragma causes <VAR>procedure</VAR> to be called. Note that
<CODE>pragma Debug</CODE> may appear within a declaration sequence, allowing
debugging procedures to be called between declarations.

</DL>



<H3><A NAME="SEC38" HREF="gnat_ug_toc.html#TOC38">Style Checking</A></H3>
<P>
<A NAME="IDX115"></A>

</P>
<P>
The -gnaty<VAR>x</VAR> switch causes the compiler to
enforce specified style rules. A limited set of style rules has been used
in writing the GNAT sources themselves. This switch allows user programs
to activate all or some of these checks. If the source program fails a
specified style check, an appropriate error message is given, preceded by
the character sequence "(style)", and the program is considered illegal.
The string <VAR>x</VAR> is a sequence of letters or digits
indicating the particular style
checks to be performed. The following checks are defined:

</P>
<DL COMPACT>

<DT><CODE>1-9 (specify indentation level)</CODE>
<DD>
If a digit from 1-9 appears in the string after <CODE>-gnaty</CODE> then proper
indentation is checked, with the digit indicating the indentation level
required. The general style of required indentation is as specified by
the examples in the Ada Reference Manual. Full line comments must be
aligned with the <CODE>--</CODE> starting on a column that is a multiple of
the alignment level.

<DT><CODE>a (check attribute casing)</CODE>
<DD>
If the letter a appears in the string after <CODE>-gnaty</CODE> then
attribute names, including the case of keywords such as <CODE>digits</CODE>
used as attributes names, must be written in mixed case, that is, the
initial letter and any letter following an underscore must be uppercase.
All other letters must be lowercase.

<DT><CODE>b (blanks not allowed at statement end)</CODE>
<DD>
If the letter b appears in the string after <CODE>-gnaty</CODE> then
trailing blanks are not allowed at the end of statements. The purpose of this
rule, together with h (no horizontal tabs), is to enforce a canonical format
for the use of blanks to separate source tokens.

<DT><CODE>c (check comments)</CODE>
<DD>
If the letter c appears in the string after <CODE>-gnaty</CODE> then
comments must meet the following set of rules:


<UL>

<LI>

The "--" that starts the column must either start in column one, or else
at least one blank must precede this sequence.

<LI>

Comments that follow other tokens on a line must have at least one blank
following the "--" at the start of the comment.

<LI>

Full line comments must have two blanks following the "--" that starts
the comment, with the following exceptions.

<LI>

A line consisting only of the "--" characters, possibly preceded by blanks
is permitted.

<LI>

A comment starting with "--!" is permitted. This allows proper processing
of the output generated by the <CODE>gnatprep</CODE> tool.

<LI>

A line consisting entirely of minus signs, possibly preceded by blanks, is
permitted. This allows the construction of box comments where lines of minus
signs are used to form the top and bottom of the box.

<LI>

If a comment starts and ends with "--" is permitted as long as at least
one blank follows the initial "--". Together with the preceding rule,
this allows the construction of box comments, as shown in the following
example:

<PRE>
   ---------------------------
   -- This is a box comment --
   -- with two text lines.  --
   ---------------------------
</PRE>

</UL>

<DT><CODE>e (check end labels)</CODE>
<DD>
If the letter e appears in the string after <CODE>-gnaty</CODE> then
optional labels on <CODE>end</CODE> statements ending subprograms are required to be
present.

<DT><CODE>f (no form feeds or vertical tabs)</CODE>
<DD>
If the letter f appears in the string after <CODE>-gnaty</CODE> then
neither form feeds nor vertical tab characters are not permitted
in the source text.

<DT><CODE>h (no horizontal tabs)</CODE>
<DD>
If the letter h appears in the string after <CODE>-gnaty</CODE> then
horizontal tab characters are not permitted in the source text.
Together with the b (no blanks at end of line) check, this
enforces a canonical form for the use of blanks to separate
source tokens.

<DT><CODE>i (check if-then layout)</CODE>
<DD>
If the letter i appears in the string after <CODE>-gnaty</CODE>,
then the keyword <CODE>then</CODE> must appear either on the same
line as corresponding <CODE>if</CODE>, or on a line on its own, lined
up under the <CODE>if</CODE> with at least one non-blank line in between
containing all or part of the condition to be tested.

<DT><CODE>k (check keyword casing)</CODE>
<DD>
If the letter k appears in the string after <CODE>-gnaty</CODE> then
all keywords must be in lower case (with the exception of keywords
such as <CODE>digits</CODE> used as attribute names to which this check
does not apply).

<DT><CODE>l (check layout)</CODE>
<DD>
If the letter l appears in the string after <CODE>-gnaty</CODE> then
layout of statement and declaration constructs must follow the
recommendations in the Ada Reference Manual, as indicated by the
form of the syntax rules. For example an <CODE>else</CODE> keyword must
be lined up with the corresponding <CODE>if</CODE> keyword.

There are two respects in which the style rule enforced by this check
option are more liberal than those in the Ada Reference Manual. First
in the case of record declarations, it is permissible to put the
<CODE>record</CODE> keyword on the same line as the <CODE>type</CODE> keyword, and
then the <CODE>end</CODE> in <CODE>end record</CODE> must line up under <CODE>type</CODE>.
For example, either of the following two layouts is acceptable:


<PRE>
   <B>type</B> q <B>is record</B>
      a : integer;
      b : integer;
   <B>end record</B>;

   <B>type</B> q <B>is</B>
      <B>record</B>
         a : integer;
         b : integer;
      <B>end record</B>;
</PRE>

Second, in the case of a block statement, a permitted alternative
is to put the block label on the same line as the <CODE>declare</CODE> or
<CODE>begin</CODE> keyword, and then line the <CODE>end</CODE> keyword up under
the block label. For example both the following are permitted:


<PRE>
   Block : <B>declare</B>
      A : Integer := 3;
   <B>begin</B>
      Proc (A, A);
   <B>end</B> Block;

   Block :
      <B>declare</B>
         A : Integer := 3;
      <B>begin</B>
         Proc (A, A);
      <B>end</B> Block;
</PRE>

The same alternative format is allowed for loops. For example, both of
the following are permitted:


<PRE>
   Clear : <B>while</B> J &#60; 10 <B>loop</B>
      A (J) := 0;
   <B>end loop</B> Clear;

   Clear :
      <B>while</B> J &#60; 10 <B>loop</B>
         A (J) := 0;
      <B>end loop</B> Clear;
</PRE>

<DT><CODE>m (check maximum line length)</CODE>
<DD>
If the letter m appears in the string after <CODE>-gnaty</CODE>
then the length of source lines must not exceed 79 characters, including
any trailing blanks. The value of 79 allows convenient display on an
80 character wide device or window, allowing for possible special
treatment of 80 character lines.

<DT><CODE>Mnnn (set maximum line length)</CODE>
<DD>
If the sequence Mnnn, where nnn is a decimal number, appears in
the string after <CODE>-gnaty</CODE> then the length of lines must not exceed the
given value.

<DT><CODE>p (check pragma casing)</CODE>
<DD>
If the letter p appears in the string after <CODE>-gnaty</CODE> then
pragma names must be written in mixed case, that is, the
initial letter and any letter following an underscore must be uppercase.
All other letters must be lowercase.

<DT><CODE>r (check references)</CODE>
<DD>
If the letter r appears in the string after <CODE>-gnaty</CODE>
then all identifier references must be cased in the same way as the
corresponding declaration. No specific casing style is imposed on
identifiers. The only requirement is for consistency of references
with declarations.

<DT><CODE>s (check separate specs)</CODE>
<DD>
If the letter s appears in the string after <CODE>-gnaty</CODE> then
separate declarations ("specs") are required for subprograms (a
body is not allowed to serve as its own declaration). The only
exception is that parameterless library level procedures are
not required to have a separate declaration. This exception covers
the most frequent form of main program procedures.

<DT><CODE>t (check token spacing)</CODE>
<DD>
If the letter t appears in the string after <CODE>-gnaty</CODE> then
the following token spacing rules are enforced:


<UL>

<LI>

The keywords <CODE>abs</CODE> and <CODE>not</CODE> must be followed by a space.

<LI>

The token <CODE>=&#62;</CODE> must be surrounded by spaces.

<LI>

The token <CODE>&#60;&#62;</CODE> must be preceded by a space or a left parenthesis.

<LI>

Binary operators other than <CODE>**</CODE> must be surrounded by spaces.
There is no restriction on the layout of the <CODE>**</CODE> binary operator.

<LI>

Colon must be surrounded by spaces.

<LI>

Colon-equal (assignment) must be surrounded by spaces.

<LI>

Comma must be the first non-blank character on the line, or be
immediately preceded by a non-blank character, and must be followed
by a space.

<LI>

Left parenthesis must be preceded by a space, and must not be followed
by a space (it can be at the end of a line).

<LI>

A right parenthesis must either be the first non-blank character on
a line, or it must be preceded by a non-blank character.

<LI>

A semicolon must not be preceded by a space, and must not be followed by
a non-blank character.

<LI>

A unary plus or minus may not be followed by a space.

<LI>

A vertical bar must be surrounded by spaces.
</UL>

In the above rules, appearing in column one is always permitted, that is,
counts as meeting either a requirement for a required preceding space,
or as meeting a requirement for no preceding space.

Appearing at the end of a line is also always permitted, that is, counts
as meeting either a requirement for a following space, or as meeting
a requirement for no following space.

</DL>

<P>
The switch
<CODE>-gnaty</CODE> on its own (that is not followed by any letters or digits),
is equivalent to <CODE>gnaty3abcefhiklmprst</CODE>, that is all checking
options are enabled, with an indentation level of 3. This is the standard
checking option that is used for the GNAT sources.

</P>


<H3><A NAME="SEC39" HREF="gnat_ug_toc.html#TOC39">Run-time Checks</A></H3>
<P>
<A NAME="IDX116"></A>
<A NAME="IDX117"></A>
<A NAME="IDX118"></A>
<A NAME="IDX119"></A>

</P>
<P>
If you compile with the default options, GNAT will insert many run-time
checks into the compiled code, including code that performs range
checking against constraints, but not arithmetic overflow checking for
integer operations (including division by zero) or checks for access
before elaboration on subprogram calls.  All other run-time checks, as
required by the Ada 95 Reference Manual, are generated by default.
The following <CODE>gcc</CODE> switches refine this default behavior:

</P>
<DL COMPACT>

<DT><CODE>-gnatp</CODE>
<DD>
<A NAME="IDX120"></A>
<A NAME="IDX121"></A>
<A NAME="IDX122"></A>
<A NAME="IDX123"></A>
Suppress all run-time checks as though <CODE>pragma Suppress (all_checks</CODE>)
had been present in the source. Use this switch to improve the performance
of the code at the expense of safety in the presence of invalid data or
program bugs.

<DT><CODE>-gnato</CODE>
<DD>
<A NAME="IDX124"></A>
<A NAME="IDX125"></A>
<A NAME="IDX126"></A>
Enables overflow checking for integer operations.
This causes GNAT to generate slower and larger executable
programs by adding code to check for both overflow and division by zero
(resulting in raising <CODE>Constraint_Error</CODE> as required by Ada
semantics).
<A NAME="IDX127"></A>
Note that the <CODE>-gnato</CODE> switch does not affect the code generated
for any floating-point operations; it applies only to integer
operations. For floating-point, GNAT has the <CODE>Machine_Overflows</CODE>
attribute set to <CODE>False</CODE> and the normal mode of operation is to
generate IEEE NaN and infinite values on overflow or invalid operations
(such as dividing 0.0 by 0.0).

<DT><CODE>-gnatE</CODE>
<DD>
<A NAME="IDX128"></A>
<A NAME="IDX129"></A>
<A NAME="IDX130"></A>
Enables dynamic checks for access-before-elaboration
on subprogram calls and generic instantiations.
For full details of the effect and use of this switch,
See section <A HREF="gnat_ug.html#SEC33">Compiling Using <CODE>gcc</CODE></A>.
</DL>

<P>
<A NAME="IDX131"></A>
The setting of these switches only controls the default setting of the
checks.  You may modify them using either <CODE>Suppress</CODE> (to remove
checks) or <CODE>Unsuppress</CODE> (to add back suppressed checks) pragmas in
the program source.

</P>


<H3><A NAME="SEC40" HREF="gnat_ug_toc.html#TOC40">Using <CODE>gcc</CODE> for Syntax Checking</A></H3>
<DL COMPACT>

<DT><CODE>-gnats</CODE>
<DD>
<A NAME="IDX132"></A>

The <CODE>s</CODE> stands for syntax.

Run GNAT in syntax checking only mode. For
example, the command


<PRE>
   $ gcc -c -gnats x.adb
</PRE>

compiles file <TT>`x.adb'</TT> in syntax-check-only mode. You can check a
series of files in a single command
, and can use wild cards to specify such a group of files.
Note that you must specify the <CODE>-c</CODE> (compile
only) flag in addition to the <CODE>-gnats</CODE> flag.
.

You may use other switches in conjunction with <CODE>-gnats</CODE>. In
particular, <CODE>-gnatl</CODE> and <CODE>-gnatv</CODE> are useful to control the
format of any generated error messages.

The output is simply the error messages, if any. No object file or ALI
file is generated by a syntax-only compilation. Also, no units other
than the one specified are accessed. For example, if a unit <CODE>X</CODE>
<CODE>with</CODE>'s a unit <CODE>Y</CODE>, compiling unit <CODE>X</CODE> in syntax
check only mode does not access the source file containing unit
<CODE>Y</CODE>.

<A NAME="IDX133"></A>
Normally, GNAT allows only a single unit in a source file. However, this
restriction does not apply in syntax-check-only mode, and it is possible
to check a file containing multiple compilation units concatenated
together. This is primarily used by the <CODE>gnatchop</CODE> utility
(see section <A HREF="gnat_ug.html#SEC75">Renaming Files Using <CODE>gnatchop</CODE></A>).
</DL>



<H3><A NAME="SEC41" HREF="gnat_ug_toc.html#TOC41">Using <CODE>gcc</CODE> for Semantic Checking</A></H3>
<DL COMPACT>

<DT><CODE>-gnatc</CODE>
<DD>
<A NAME="IDX134"></A>

The <CODE>c</CODE> stands for check.
Causes the compiler to operate in semantic check mode,
with full checking for all illegalities specified in the
Ada 95 Reference Manual, but without generation of any source code (no object
or ALI file generated).

Because dependent files must be accessed, you must follow the GNAT
semantic restrictions on file structuring to operate in this mode:


<UL>
<LI>

The needed source files must be accessible (see section <A HREF="gnat_ug.html#SEC49">Search Paths and the Run-Time Library (RTL)</A>).

<LI>

Each file must contain only one compilation unit.

<LI>

The file name and unit name must match (see section <A HREF="gnat_ug.html#SEC17">File Naming Rules</A>).
</UL>

The output consists of error messages as appropriate. No object file or
ALI file is generated. The checking corresponds exactly to the notion of
legality in the Ada 95 Reference Manual.

Any unit can be compiled in semantics-checking-only mode, including
units that would not normally be compiled (subunits,
and specifications where a separate body is present).
</DL>



<H3><A NAME="SEC42" HREF="gnat_ug_toc.html#TOC42">Compiling Ada 83 Programs</A></H3>
<DL COMPACT>

<DT><CODE>-gnat83</CODE>
<DD>
<A NAME="IDX135"></A>
 
<A NAME="IDX136"></A>
<A NAME="IDX137"></A>

Although GNAT is primarily an Ada 95 compiler, it accepts this switch to
specify that an Ada 83 program is to be compiled in Ada83 mode. If you specify
this switch, GNAT rejects most Ada 95 extensions and applies Ada 83 semantics
where this can be done easily.
It is not possible to guarantee this switch does a perfect
job; for example, some subtle tests, such as are
found in earlier ACVC tests (that have been removed from the ACVC suite for Ada
95), may not compile correctly. However, for most purposes, using
this switch should help to ensure that programs that compile correctly
under the <CODE>-gnat83</CODE> switch can be ported easily to an Ada 83
compiler. This is the main use of the switch.

With few exceptions (most notably the need to use <CODE>&#60;&#62;</CODE> on
<A NAME="IDX138"></A>
unconstrained generic formal parameters, the use of the new Ada 95
keywords, and the use of packages
with optional bodies), it is not necessary to use the
<CODE>-gnat83</CODE> switch when compiling Ada 83 programs, because, with rare
exceptions, Ada 95 is upwardly compatible with Ada 83. This
means that a correct Ada 83 program is usually also a correct Ada 95
program.

<DT><CODE>-gnat95</CODE>
<DD>
<A NAME="IDX139"></A>
This switch specifies normal Ada 95 mode, and cancels the effect of
any previously given -gnat83 switch.

</DL>


<H3><A NAME="SEC43" HREF="gnat_ug_toc.html#TOC43">Reference Manual Style Checking</A></H3>
<DL COMPACT>

<DT><CODE>-gnatr</CODE>
<DD>
<A NAME="IDX140"></A>

Normally, GNAT permits any source layout consistent with the Ada 95
reference manual requirements. This switch
(<SAMP>`r'</SAMP> is for "reference manual")
enforces the layout conventions suggested by the examples and syntax
rules of the Ada 95 Language Reference Manual. For example, an <CODE>else</CODE>
must line up with an <CODE>if</CODE> and code in the <CODE>then</CODE> and
<CODE>else</CODE> parts must be indented. The compiler treats violations of
the layout rules as syntax errors if you specify this switch.

<DT><CODE>-gnatg</CODE>
<DD>
<A NAME="IDX141"></A>
Enforces a set of style conventions that correspond to the style used in
the GNAT source code.  All compiler units are always compiled with the
<CODE>-gnatg</CODE> switch specified.

<A NAME="IDX142"></A>
You can find the full documentation for the style conventions imposed by
<CODE>-gnatg</CODE> in the body of the package <CODE>Style</CODE> in the
compiler sources (in the file <TT>`style.adb'</TT>).

<A NAME="IDX143"></A>
You should not normally use the <CODE>-gnatg</CODE> switch. However, you
<EM>must</EM> use <CODE>-gnatg</CODE> for compiling any language-defined unit,
or for adding children to any language-defined unit other than
<CODE>Standard</CODE>.
</DL>


<H3><A NAME="SEC44" HREF="gnat_ug_toc.html#TOC44">Character Set Control</A></H3>
<DL COMPACT>

<DT><CODE>-gnati<VAR>c</VAR></CODE>
<DD>
<A NAME="IDX144"></A>

Normally GNAT recognizes the Latin-1 character set in source program
identifiers, as described in the Ada 95 Reference Manual.
This switch causes
GNAT to recognize alternate character sets in identifiers.  <VAR>c</VAR> is a
single character  indicating the character set, as follows:

<DL COMPACT>

<DT><CODE>1</CODE>
<DD>
Latin-1 identifiers

<DT><CODE>2</CODE>
<DD>
Latin-2 letters allowed in identifiers

<DT><CODE>3</CODE>
<DD>
Latin-3 letters allowed in identifiers

<DT><CODE>4</CODE>
<DD>
Latin-4 letters allowed in identifiers

<DT><CODE>p</CODE>
<DD>
IBM PC letters (code page 437) allowed in identifiers

<DT><CODE>8</CODE>
<DD>
IBM PC letters (code page 850) allowed in identifiers

<DT><CODE>f</CODE>
<DD>
Full upper-half codes allowed in identifiers

<DT><CODE>n</CODE>
<DD>
No upper-half codes allowed in identifiers

<DT><CODE>w</CODE>
<DD>
Wide-character codes allowed in identifiers
</DL>

See section <A HREF="gnat_ug.html#SEC13">Foreign Language Representation</A>, for full details on the
implementation of these character sets.

<DT><CODE>-gnatW<VAR>e</VAR></CODE>
<DD>
<A NAME="IDX145"></A>
Specify the method of encoding for wide characters.
<VAR>e</VAR> is one of the following:

<DL COMPACT>

<DT><CODE>h</CODE>
<DD>
Hex encoding (brackets coding also recognized)

<DT><CODE>u</CODE>
<DD>
Upper half encoding (brackets encoding also recognized)

<DT><CODE>s</CODE>
<DD>
Shift/JIS encoding (brackets encoding also recognized)

<DT><CODE>e</CODE>
<DD>
EUC encoding (brackets encoding also recognized)

<DT><CODE>8</CODE>
<DD>
UTF-8 encoding (brackets encoding also recognized)

<DT><CODE>b</CODE>
<DD>
Brackets encoding only (default value)
</DL>
For full details on the these encoding
methods see See section <A HREF="gnat_ug.html#SEC16">Wide Character Encodings</A>.
Note that brackets coding is always accepted, even if one of the other
options is specified, so for example <CODE>-gnatW8</CODE> specifies that both
brackets and <CODE>UTF-8</CODE> encodings will be recognized. The units that are
with'ed directly or indirectly will be scanned using the specified
representation scheme, and so if one of the non-brackets scheme is
used, it must be used consistently throughout the program. However,
since brackets encoding is always recognized, it may be conveniently
used in standard libraries, allowing these libraries to be used with
any of the available coding schemes.
scheme. If no <CODE>-gnatW?</CODE> parameter is present, then the default
representation is Brackets encoding only.

Note that the wide character representation that is specified (explicitly
or by default) for the main program also acts as the default encoding used
for Wide_Text_IO files if not specifically overridden by a WCEM form
parameter.

</DL>


<H3><A NAME="SEC45" HREF="gnat_ug_toc.html#TOC45">File Naming Control</A></H3>

<DL COMPACT>

<DT><CODE>-gnatk<VAR>n</VAR></CODE>
<DD>
<A NAME="IDX146"></A>
Activates file name "krunching". <VAR>n</VAR>, a decimal integer in the range
1-999, indicates the maximum allowable length of a file name (not
including the <TT>`.ads'</TT> or <TT>`.adb'</TT> extension). The default is not
to enable file name krunching.

For the source file naming rules, See section <A HREF="gnat_ug.html#SEC17">File Naming Rules</A>.
</DL>



<H3><A NAME="SEC46" HREF="gnat_ug_toc.html#TOC46">Subprogram Inlining Control</A></H3>

<DL COMPACT>

<DT><CODE>-gnatn</CODE>
<DD>
<A NAME="IDX147"></A>
The <CODE>n</CODE> here is intended to suggest the first syllable of the
word "inline".
GNAT recognizes and processes <CODE>Inline</CODE> pragmas. However, for the
inlining to actually occur, optimization must be enabled.  To enable
inlining across unit boundaries, this is, inlining a call in one unit of
a subprogram declared in a <CODE>with</CODE>'ed unit, you must also specify
this switch.
In the absence of this switch, GNAT does not attempt
inlining across units and does not need to access the bodies of
subprograms for which <CODE>pragma Inline</CODE> is specified if they are not
in the current unit.

If you specify this switch the compiler will access these bodies,
creating an extra source dependency for the resulting object file, and
where possible, the call will be inlined. For further details on when inlining is possible
see See section <A HREF="gnat_ug.html#SEC163">Inlining of Subprograms</A>.

<DT><CODE>-gnatN</CODE>
<DD>
This switch enforces a more extreme form of inlining across unit
boundaries. It causes the compiler to proceed as though the normal
(pragma) inlining switch was set, and to assume that there is a
pragma <CODE>Inline</CODE> for every subprogram referenced by the compiled
unit.

</DL>



<H3><A NAME="SEC47" HREF="gnat_ug_toc.html#TOC47">Auxiliary Output Control</A></H3>

<DL COMPACT>

<DT><CODE>-gnatt</CODE>
<DD>
<A NAME="IDX148"></A>
<A NAME="IDX149"></A>
<A NAME="IDX150"></A>
Cause GNAT to write the internal tree for a unit to a file (with the
extension <TT>`.atb'</TT> for a body or <TT>`.ats'</TT> for a spec).  This is
not normally required, but is used by separate analysis tools. Typically
these tools do the necessary compilations automatically, so you should
never have to specify this switch in normal operation.

<DT><CODE>-gnatu</CODE>
<DD>
<A NAME="IDX151"></A>
Print a list of units required by this compilation on <CODE>stdout</CODE>.
The listing includes all units on which the unit being compiled depends
either directly or indirectly.
</DL>



<H3><A NAME="SEC48" HREF="gnat_ug_toc.html#TOC48">Debugging Control</A></H3>

<DL COMPACT>

<DT><CODE>-gnatd<VAR>x</VAR></CODE>
<DD>
<A NAME="IDX152"></A>
 
Activate internal debugging switches.  <VAR>x</VAR> is a letter or digit, or
string of letters or digits, which specifies the type of debugging
outputs desired.  Normally these are used only for internal development
or system debugging purposes. You can find full documentation for these
switches in the body of the <CODE>Debug</CODE> unit in the compiler source
file <TT>`debug.adb'</TT>.

<DT><CODE>-gnatG</CODE>
<DD>
<A NAME="IDX153"></A>
This switch causes the compiler to generate auxiliary output containing
a pseudo-source listing of the generated expanded code. Like most Ada
compilers, GNAT works by first transforming the high level Ada code into
lower level constructs. For example, tasking operations are transformed
into calls to the tasking run-time routines. A unique capability of GNAT
is to list this expanded code in a form very close to normal Ada source.
This is very useful in understanding the implications of various Ada
usage on the efficiency of the generated code. There are many cases in
Ada (e.g. the use of controlled types), where simple Ada statements can
generate a lot of run-time code. By using <CODE>-gnatG</CODE> you can identify
these cases, and consider whether it may be desirable to modify the coding
approach to improve efficiency.

The format of the output is very similar to standard Ada source, and is
easily understood by an Ada programmer. The following special syntactic
additions correspond to low level features used in the generated code that
do not have any exact analogies in pure Ada source form:

<DT><CODE>-gnatD</CODE>
<DD>
<A NAME="IDX154"></A>
This switch is used in conjunction with <CODE>-gnatG</CODE> to cause the expanded
source, as described above to be written to files with names
<TT>`xxx.dg'</TT>, where <TT>`xxx'</TT> is the normal file name,
for example, if the source file name is <TT>`hello.adb'</TT>,
then a file <TT>`hello.adb.dg'</TT> will be written.
The debugging information generated
by the <CODE>gcc</CODE> <CODE>-g</CODE> switch will refer to the generated
<TT>`xxx.dg'</TT> file. This allows you to do source level debugging using
the generated code which is sometimes useful for complex code, for example
to find out exactly which part of a complex construction raised an
exception.

</DL>

<DL COMPACT>

<DT><CODE>new <VAR>xxx</VAR> [storage_pool = <VAR>yyy</VAR>]</CODE>
<DD>
Shows the storage pool being used for an allocator.

<DT><CODE>at end <VAR>procedure-name</VAR>;</CODE>
<DD>
Shows the finalization (cleanup) procedure for a scope.

<DT><CODE>(if <VAR>expr</VAR> then <VAR>expr</VAR> else <VAR>expr</VAR>)</CODE>
<DD>
Conditional expression equivalent to the <CODE>x?y:z</CODE> construction in C.

<DT><CODE><VAR>target</VAR>^(<VAR>source</VAR>)</CODE>
<DD>
A conversion with floating-point truncation instead of rounding.

<DT><CODE><VAR>target</VAR>?(<VAR>source</VAR>)</CODE>
<DD>
A conversion that bypasses normal Ada semantic checking. In particular
enumeration types and fixed-point types are treated simply as integers.

<DT><CODE><VAR>target</VAR>?^(<VAR>source</VAR>)</CODE>
<DD>
Combines the above two cases.

<DT><CODE><VAR>x</VAR> #/ <VAR>y</VAR></CODE>
<DD>
<DT><CODE><VAR>x</VAR> #mod <VAR>y</VAR></CODE>
<DD>
<DT><CODE><VAR>x</VAR> #* <VAR>y</VAR></CODE>
<DD>
<DT><CODE><VAR>x</VAR> #rem <VAR>y</VAR></CODE>
<DD>
A division or multiplication of fixed-point values which are treated as
integers without any kind of scaling.

<DT><CODE>free <VAR>expr</VAR> [storage_pool = <VAR>xxx</VAR>]</CODE>
<DD>
Shows the storage pool associated with a <CODE>free</CODE> statement.

<DT><CODE>freeze <VAR>typename</VAR> [<VAR>actions</VAR>]</CODE>
<DD>
Shows the point at which <VAR>typename</VAR> is frozen, with possible
associated actions to be performed at the freeze point.

<DT><CODE>reference <VAR>itype</VAR></CODE>
<DD>
Reference (and hence definition) to internal type <VAR>itype</VAR>.

<DT><CODE><VAR>function-name</VAR>! (<VAR>arg</VAR>, <VAR>arg</VAR>, <VAR>arg</VAR>)</CODE>
<DD>
Intrinsic function call.

<DT><CODE><VAR>labelname</VAR> : label</CODE>
<DD>
Declaration of label <VAR>labelname</VAR>.

<DT><CODE><VAR>expr</VAR> &#38;&#38; <VAR>expr</VAR> &#38;&#38; <VAR>expr</VAR> ... &#38;&#38; <VAR>expr</VAR></CODE>
<DD>
A multiple concatenation (same effect as <VAR>expr</VAR> &#38; <VAR>expr</VAR> &#38;
<VAR>expr</VAR>, but handled more efficiently).

<DT><CODE>[constraint_error]</CODE>
<DD>
Raise the <CODE>Constraint_Error</CODE> exception.

<DT><CODE><VAR>expression</VAR>'reference</CODE>
<DD>
A pointer to the result of evaluating <VAR>expression</VAR>.

<DT><CODE><VAR>target-type</VAR>!(<VAR>source-expression</VAR>)</CODE>
<DD>
An unchecked conversion of <VAR>source-expression</VAR> to <VAR>target-type</VAR>.

<DT><CODE>[<VAR>numerator</VAR>/<VAR>denominator</VAR>]</CODE>
<DD>
Used to represent internal real literals (that) have no exact
representation in base 2-16 (for example, the result of compile time
evaluation of the expression 1.0/27.0).

</DL>


<H2><A NAME="SEC49" HREF="gnat_ug_toc.html#TOC49">Search Paths and the Run-Time Library (RTL)</A></H2>

<P>
With the GNAT source-based library system, the compiler must be able to
find source files for units that are needed by the unit being compiled.
Search paths are used to guide this process.

</P>
<P>
The compiler compiles one source file whose name must be given
explicitly on the command line.  In other words, no searching is done
for this file. To find all other source files that are needed (the most
common being the specs of units), the compiler examines the following
directories, in the following order:

</P>

<OL>
<LI>

The directory containing the source file of the main unit being compiled
(the file name on the command line).

<LI>

Each directory named by an <CODE>-I</CODE> switch given on the <CODE>gcc</CODE>
command line, in the order given.

<LI>

<A NAME="IDX155"></A>
Each of the directories listed in the value of the
<CODE>ADA_INCLUDE_PATH</CODE> environment variable.
Construct this value
exactly as the <CODE>PATH</CODE> environment variable: a list of directory
names separated by colons.

<LI>

The default location for the GNAT Run Time Library (RTL) source files.
This is determined at the time GNAT is built and installed on your
system.
</OL>

<P>
Specifying the switch <CODE>-I-</CODE>
inhibits the use of the directory
containing the source file named in the command line.  You can still
have this directory on your search path, but in this case it must be
explicitly requested with a <CODE>-I</CODE> switch.

</P>
<P>
Specifying the switch <CODE>-nostdinc</CODE>
inhibits the search of the default location for the GNAT Run Time
Library (RTL) source files.

</P>
<P>
The compiler outputs its object files and ALI files in the current
working directory.
Caution: The object file can be redirected with the <CODE>-o</CODE> switch;
however, <CODE>gcc</CODE> and <CODE>gnat1</CODE> have not been coordinated on this
so the ALI file will not go to the right place.  Therefore, you should
avoid using the <CODE>-o</CODE> switch.

</P>
<P>
<A NAME="IDX156"></A>
The packages <CODE>Ada</CODE>, <CODE>System</CODE>, and <CODE>Interfaces</CODE> and their
children make up the GNAT RTL, together with the simple <CODE>System.IO</CODE>
package used in the "Hello World" example. The sources for these units
are needed by the compiler and are kept together in one directory. Not
all of the bodies are needed, but all of the sources are kept together
anyway.  In a normal installation, you need not specify these directory
names when compiling or binding.  Either the environment variables or
the built-in defaults cause these files to be found.

</P>
<P>
In addition to the language-defined hierarchies (System, Ada and
Interfaces), the GNAT distribution provides a fourth hierarchy,
consisting of child units of GNAT. This is a collection of generally
useful routines. See the GNAT Reference Manual for further details.

</P>
<P>
Besides simplifying access to the RTL, a major use of search paths is
in compiling sources from multiple directories. This can make
development environments much more flexible.

</P>


<H2><A NAME="SEC50" HREF="gnat_ug_toc.html#TOC50">Order of Compilation Issues</A></H2>

<P>
If, in our earlier example, there was a spec for the <CODE>hello</CODE>
procedure, it would be contained in the file <TT>`hello.ads'</TT>; yet this
file would not have to be explicitly compiled. This is the result of the
model we chose to implement library management. Some of the consequences
of this model are as follows:

</P>

<UL>
<LI>

There is no point in compiling specs (except for package
specs with no bodies) because these are compiled as needed by clients. If
you attempt a useless compilation, you will receive an error message.
It is also useless to compile subunits because they are compiled as needed
by the parent.

<LI>

There are no order of compilation requirements: performing a
compilation never obsoletes anything. The only way you can obsolete
something and require recompilations is to modify one of the
source files on which it depends.

<LI>

There is no library as such, apart from the ALI files (see section <A HREF="gnat_ug.html#SEC21">The Ada Library Information Files</A>, for information on the format of these
files). For now we find it convenient to create separate ALI files, but
eventually the information therein may be incorporated into the object
file directly.

<LI>

When you compile a unit, the source files for the specs of all units
that it <CODE>with</CODE>'s, all its subunits, and the bodies of any generics it
instantiates must be available (reachable by the search-paths mechanism
described above), or you will receive a fatal error message.
</UL>



<H2><A NAME="SEC51" HREF="gnat_ug_toc.html#TOC51">Examples</A></H2>

<P>
The following are some typical Ada compilation command line examples:

</P>
<DL COMPACT>

<DT><CODE>$ gcc -c xyz.adb</CODE>
<DD>
Compile body in file <TT>`xyz.adb'</TT> with all default options.

<DT><CODE>$ gcc -c -O2 -gnata xyz-def.adb</CODE>
<DD>
Compile the child unit package in file <TT>`xyz-def.adb'</TT> with extensive
optimizations, and pragma <CODE>Assert</CODE>/<CODE>Debug</CODE> statements
enabled.

<DT><CODE>$ gcc -c -gnatc abc-def.adb</CODE>
<DD>
Compile the subunit in file <TT>`abc-def.adb'</TT> in semantic-checking-only
mode.
</DL>



<H1><A NAME="SEC52" HREF="gnat_ug_toc.html#TOC52">Binding Using <CODE>gnatbind</CODE></A></H1>
<P>
<A NAME="IDX157"></A>

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC53">Running gnatbind</A>
<LI><A HREF="gnat_ug.html#SEC54">Consistency-Checking Modes</A>
<LI><A HREF="gnat_ug.html#SEC55">Binder Error Message Control</A>
<LI><A HREF="gnat_ug.html#SEC56">Elaboration Control</A>
<LI><A HREF="gnat_ug.html#SEC57">Output Control</A>
<LI><A HREF="gnat_ug.html#SEC58">Binding with Non-Ada Main Programs</A>
<LI><A HREF="gnat_ug.html#SEC59">Binding Programs with no Main Subprogram</A>
<LI><A HREF="gnat_ug.html#SEC60">Summary of Binder Switches</A>
<LI><A HREF="gnat_ug.html#SEC61">Command-Line Access</A>
<LI><A HREF="gnat_ug.html#SEC62">Search Paths for gnatbind</A>
<LI><A HREF="gnat_ug.html#SEC63">Examples of gnatbind Usage</A>
</UL>

<P>
This chapter describes the GNAT binder, <CODE>gnatbind</CODE>, which is used
to bind compiled GNAT objects.  The <CODE>gnatbind</CODE> program performs
four separate functions:

</P>

<OL>
<LI>

Checks that a program is consistent, in accordance with the rules in
Chapter 10 of the Ada 95 Reference Manual. In particular, error
messages are generated if a program uses inconsistent versions of a
given unit.

<LI>

Checks that an acceptable order of elaboration exists for the program
and issues an error message if it cannot find an order of elaboration
that satisfies the rules in Chapter 10 of the Ada 95 Language Manual.

<LI>

Generates a main program incorporating the given elaboration order.
This program is a small C source file that must be subsequently compiled
using the C compiler. The two most important functions of this program
are to call the elaboration routines of units in an appropriate order
and to call the main program.

<LI>

Determines the set of object files required by the given main program.
This information is output in the forms of comments in the generated C program,
to be read by the <CODE>gnatlink</CODE> utility used to link the Ada application.
</OL>



<H2><A NAME="SEC53" HREF="gnat_ug_toc.html#TOC53">Running <CODE>gnatbind</CODE></A></H2>

<P>
The form of the <CODE>gnatbind</CODE> command is

</P>

<PRE>
   $ gnatbind [<VAR>switches</VAR>] <VAR>mainprog</VAR>[.ali] [<VAR>switches</VAR>]
</PRE>

<P>
where <VAR>mainprog</VAR>.adb is the Ada file containing the main program
unit body. If no switches are specified, <CODE>gnatbind</CODE> constructs an Ada
package in two files whose names are
<TT>`b~<VAR>ada_main</VAR>.ads'</TT>, and
<TT>`b~<VAR>ada_main</VAR>.adb'</TT>.
For example, if given the
parameter <SAMP>`hello.ali'</SAMP>, for a main program contained in file
<TT>`hello.adb'</TT>, the binder output files would be <TT>`b~hello.ads'</TT>
and <TT>`b~hello.adb'</TT>.

</P>
<P>
When doing consistency checking, the binder takes any source files it
can locate into consideration. For example, if the binder determines
that the given main program requires the package <CODE>Pack</CODE>, whose ALI
file is <TT>`pack.ali'</TT> and whose corresponding source spec file is
<TT>`pack.ads'</TT>, it attempts to locate the source file <TT>`pack.ads'</TT>
(using the same search path conventions as previously described for the
<CODE>gcc</CODE> command). If it can locate this source file, it checks that
the time stamps
or source checksums of the source and its references to in <TT>`ali'</TT> files
match. In other words, any <TT>`ali'</TT> files that mentions this spec must have
resulted from compiling this version of the source file (or in the case
where the source checksums match, a version close enough that the
difference does not matter).

</P>
<P>
<A NAME="IDX158"></A>
The effect of this consistency checking, which includes source files, is
that the binder ensures that the program is consistent with the latest
version of the source files that can be located at bind time. Editing a
source file without compiling files that depend on the source file cause
error messages to be generated by the binder.

</P>
<P>
For example, suppose you have a main program <TT>`hello.adb'</TT> and a
package <CODE>P</CODE>, from file <TT>`p.ads'</TT> and you perform the following
steps:

</P>

<OL>
<LI>

Enter <CODE>gcc -c hello.adb</CODE> to compile the main program.

<LI>

Enter <CODE>gcc -c p.ads</CODE> to compile package <CODE>P</CODE>.

<LI>

Edit file <TT>`p.ads'</TT>.

<LI>

Enter <CODE>gnatbind hello</CODE>.
</OL>

<P>
At this point, the file <TT>`p.ali'</TT> contains an out-of-date time stamp
because the file <TT>`p.ads'</TT> has been edited. The attempt at binding
fails, and the binder generates the following error messages:

</P>

<PRE>
   error: "hello.adb" must be recompiled ("p.ads" has been modified)
   error: "p.ads" has been modified and must be recompiled
</PRE>

<P>
Now both files must be recompiled as indicated, and then the bind can
succeed, generating a main program.  You need not normally be concerned
with the contents of this file, but it is similar to the following (when
using -C):

</P>

<PRE>

extern int gnat_argc;
extern char **gnat_argv;
extern char **gnat_envp;
extern int gnat_exit_status;
void adafinal ();
void adainit ()
{
   __gnat_set_globals (
      -1,    /* Main_Priority              */
      -1,    /* Time_Slice_Value           */
      ' ',   /* Locking_Policy             */
      ' ',   /* Queuing_Policy             */
      ' ',   /* Tasking_Dispatching_Policy */
      adafinal);
   system___elabs ();
/* system__standard_library___elabs (); */
/* system__task_specific_data___elabs (); */
/* system__tasking_soft_links___elabs (); */
   system__tasking_soft_links___elabb ();
/* system__task_specific_data___elabb (); */
/* system__standard_library___elabb (); */
/* m___elabb (); */
}
void adafinal () {
}
int main (argc, argv, envp)
    int argc;
    char **argv;
    char **envp;
{
   gnat_argc = argc;
   gnat_argv = argv;
   gnat_envp = envp;

   __gnat_initialize();
   adainit();

   _ada_m ();

   adafinal();
   __gnat_finalize();
   exit (gnat_exit_status);
}
unsigned mB = 0x2B0EB17F;
unsigned system__standard_libraryB = 0x0122ED49;
unsigned system__standard_libraryS = 0x79B018CE;
unsigned systemS = 0x08FBDA7E;
unsigned system__task_specific_dataB = 0x6CC7367B;
unsigned system__task_specific_dataS = 0x47178527;
unsigned system__tasking_soft_linksB = 0x5A75A73C;
unsigned system__tasking_soft_linksS = 0x3012AFCB;
/* BEGIN Object file/option list
./system.o
./s-tasoli.o
./s-taspda.o
./s-stalib.o
./m.o
   END Object file/option list */
</PRE>

<P>
The call to <CODE>__gnat_set_globals</CODE> establishes program parameters,
including the priority of the main task, and parameters for tasking
control. It also passes the address of the finalization routine so
that it can be called at the end of program execution.

</P>
<P>
<A NAME="IDX159"></A>
<A NAME="IDX160"></A>
<A NAME="IDX161"></A>
<A NAME="IDX162"></A>
<A NAME="IDX163"></A>

</P>
<P>
Next there is code to save the <CODE>argc</CODE> and <CODE>argv</CODE> values for
later access by the <CODE>Ada.Command_Line</CODE> package. The variable
<CODE>gnat_exit_status</CODE> saves the exit status set by calls to
<CODE>Ada.Command_Line.Set_Exit_Status</CODE> and is used to return an exit
status to the system.

</P>
<P>
<A NAME="IDX164"></A>
<A NAME="IDX165"></A>
The call to <CODE>__gnat_initialize</CODE> and the corresponding call at the
end of execution to <CODE>__gnat_finalize</CODE> allow any specialized
initialization and finalization code to be hooked in.  The default
versions of these routines do nothing.

</P>
<P>
<A NAME="IDX166"></A>
The calls to <CODE>xxx___elabb</CODE> and
<CODE>xxx___elabs</CODE> perform necessary elaboration of the bodies and
specs respectively of units in the program. These calls are commented
out if the unit in question has no elaboration code.

</P>
<P>
The call to
<CODE>m</CODE>
is the call to the main program.

</P>
<P>
<A NAME="IDX167"></A>
<A NAME="IDX168"></A>
The list of unsigned constants gives the version number information.
Version numbers are computed by combining time stamps of a unit and all
units on which it depends. These values are used for implementation of
the <CODE>Version</CODE> and <CODE>Body_Version</CODE> attributes.

</P>
<P>
Finally, a set of comments gives the full names of all the object files
that must be linked to provide the Ada component of the program. As seen in
the previous example, this list includes the files explicitly supplied
and referenced by the user as well as implicitly referenced run-time unit
files. The latter are omitted if the corresponding units reside in
shared libraries. The directory names for the run-time units depend on
the system configuration. See section <A HREF="gnat_ug.html#SEC57">Output Control</A>.

</P>


<H2><A NAME="SEC54" HREF="gnat_ug_toc.html#TOC54">Consistency-Checking Modes</A></H2>

<P>
As described in the previous section, by default <CODE>gnatbind</CODE> checks
that object files are consistent with one another and are consistent
with any source files it can locate. The following switches control binder
access to sources.

</P>
<DL COMPACT>

<DT><CODE>-s</CODE>
<DD>
<A NAME="IDX169"></A>
Require source files to be present. In this mode, the binder must be
able to locate all source files that are referenced, in order to check
their consistency. In normal mode, if a source file cannot be located it
is simply ignored. If you specify this switch, a missing source
file is an error.

<DT><CODE>-x</CODE>
<DD>
<A NAME="IDX170"></A>
Exclude source files. In this mode, the binder only checks that ALI
files are consistent with one another. Source files are not accessed.
The binder runs faster in this mode, and there is still a guarantee that
the resulting program is self-consistent.
If a source file has been edited since it was last compiled, and you
specify this switch, the binder will not detect that the object
file is out of date with respect to the source file. Note that this is the
mode that is automatically used by <CODE>gnatmake</CODE> because in this
case the checking against sources has already been performed by
<CODE>gnatmake</CODE> in the course of compilation (i.e. before binding).

</DL>



<H2><A NAME="SEC55" HREF="gnat_ug_toc.html#TOC55">Binder Error Message Control</A></H2>

<P>
The following switches provide control over the generation of error
messages from the binder:

</P>
<DL COMPACT>

<DT><CODE>-v</CODE>
<DD>
<A NAME="IDX171"></A>
Verbose mode. In the normal mode, brief error messages are generated to
<CODE>stderr</CODE>. If this switch is present, a header is written
to <CODE>stdout</CODE> and any error messages are directed to <CODE>stdout</CODE>.
All that is written to <CODE>stderr</CODE> is a brief summary message.

<DT><CODE>-b</CODE>
<DD>
<A NAME="IDX172"></A>
Generate brief error messages to <CODE>stderr</CODE> even if verbose mode is
specified. This is relevant only when used with the
<CODE>-v</CODE> switch.

<DT><CODE>-m<VAR>n</VAR></CODE>
<DD>
<A NAME="IDX173"></A>
Limits the number of error messages to <VAR>n</VAR>, a decimal integer in the
range 1-999. The binder terminates immediately if this limit is reached.

<DT><CODE>-M<VAR>xxx</VAR></CODE>
<DD>
<A NAME="IDX174"></A>
Renames the generated main program from <CODE>main</CODE> to <CODE>xxx</CODE>.
This is useful in the case of some cross-building environments, where
the actual main program is separate from the one generated
by <CODE>gnatbind</CODE>.

<DT><CODE>-ws</CODE>
<DD>
<A NAME="IDX175"></A>
<A NAME="IDX176"></A>
Suppress all warning messages.

<DT><CODE>-we</CODE>
<DD>
<A NAME="IDX177"></A>
Treat any warning messages as fatal errors.

<DT><CODE>-t</CODE>
<DD>
<A NAME="IDX178"></A>
<A NAME="IDX179"></A>
Ignore time stamp errors. Any time stamp error messages are treated as
warning messages. This switch essentially disconnects the normal
consistency checking, and the resulting program may have undefined
semantics if inconsistent units are present. <EM>This means that
<CODE>-t</CODE> should be used only in unusual situations,
with extreme care.</EM>
</DL>



<H2><A NAME="SEC56" HREF="gnat_ug_toc.html#TOC56">Elaboration Control</A></H2>

<P>
The following switches provide additional control over the elaboration
order. For full details see See section <A HREF="gnat_ug.html#SEC84">Elaboration Order Handling in GNAT</A>.

</P>
<DL COMPACT>

<DT><CODE>-f</CODE>
<DD>
<A NAME="IDX180"></A>
Instructs the binder to ignore directives from the compiler about
implied <CODE>Elaborate_All</CODE> pragmas, and to use full Ada 95 Reference
Manual semantics in an attempt to find a legal elaboration order,
even if it seems likely that this order will cause an elaboration
exception.

<DT><CODE>-p</CODE>
<DD>
<A NAME="IDX181"></A>
Normally the binder attempts to choose an elaboration order that is
likely to minimize the likelihood of an elaboration order error resulting
in raising a <CODE>Program_Error</CODE> exception. This switch reverses the
action of the binder, and requests that it deliberately choose an order
that is likely to maximize the likelihood of an elaboration error.
This is useful in ensuring portability and avoiding dependence on
accidental fortuitous elaboration ordering.
</DL>



<H2><A NAME="SEC57" HREF="gnat_ug_toc.html#TOC57">Output Control</A></H2>

<P>
The following switches allow additional control over the output
generated by the binder.

</P>
<DL COMPACT>

<DT><CODE>-A</CODE>
<DD>
<A NAME="IDX182"></A>
Generate binder program in Ada (default). The binder program is named
<TT>`b~<VAR>mainprog</VAR>.adb'</TT> by default. This can be changed with
<CODE>-o</CODE> <CODE>gnatbind</CODE> option.

<DT><CODE>-C</CODE>
<DD>
<A NAME="IDX183"></A>
Generate binder program in C. The binder program is named
<TT>`b_<VAR>mainprog</VAR>.c'</TT>. This can be changed with <CODE>-o</CODE> <CODE>gnatbind</CODE>
option.

<DT><CODE>-e</CODE>
<DD>
<A NAME="IDX184"></A>
Output complete list of elaboration-order dependencies, showing the
reason for each dependency. This output can be rather extensive but may
be useful in diagnosing problems with elaboration order. The output is
written to <CODE>stdout</CODE>.

<DT><CODE>-h</CODE>
<DD>
<A NAME="IDX185"></A>
Output usage information. The output is written to <CODE>stdout</CODE>.

<DT><CODE>-l</CODE>
<DD>
<A NAME="IDX186"></A>
Output chosen elaboration order. The output is written to <CODE>stdout</CODE>.

<DT><CODE>-O</CODE>
<DD>
<A NAME="IDX187"></A>
Output full names of all the object files that must be linked to provide
the Ada component of the program. The output is written to <CODE>stdout</CODE>.
This list includes the files explicitly supplied and referenced by the user
as well as implicitly referenced run-time unit files. The latter are
omitted if the corresponding units reside in shared libraries. The
directory names for the run-time units depend on the system configuration.

<DT><CODE>-o <VAR>file</VAR></CODE>
<DD>
<A NAME="IDX188"></A>
Set name of output file to <VAR>file</VAR> instead of the normal
<TT>`b~<VAR>mainprog</VAR>.adb'</TT> default.  Note that <VAR>file</VAR> denote the Ada
binder generated body filename. In C mode you would normally give
<VAR>file</VAR> an extension of <TT>`.c'</TT> because it will be a C source program.
Note that if this option is used, then linking must be done manually.
It is not possible to use gnatlink in this case, since it cannot locate
the binder file.

<DT><CODE>-c</CODE>
<DD>
<A NAME="IDX189"></A>
Check only. Do not generate the binder output file. In this mode the
binder performs all error checks but does not generate an output file.
</DL>



<H2><A NAME="SEC58" HREF="gnat_ug_toc.html#TOC58">Binding with Non-Ada Main Programs</A></H2>

<P>
In our description so far we have assumed that the main
program is in Ada, and that the task of the binder is to generate a
corresponding function <CODE>main</CODE> that invokes this Ada main
program.  GNAT also supports the building of executable programs where
the main program is not in Ada, but some of the called routines are
written in Ada and compiled using GNAT (see section <A HREF="gnat_ug.html#SEC24">Mixed Language Programming</A>).
The following switch is used in this situation:

</P>
<DL COMPACT>

<DT><CODE>-n</CODE>
<DD>
<A NAME="IDX190"></A>
No main program. The main program is not in Ada.
</DL>

<P>
In this case, most of the functions of the binder are still required,
but instead of generating a main program, the binder generates a file
containing the following callable routines:

</P>
<DL COMPACT>

<DT><CODE>adainit</CODE>
<DD>
<A NAME="IDX191"></A>
You must call this routine to initialize the Ada part of the program by
calling the necessary elaboration routines. A call to <CODE>adainit</CODE> is
required before the first call to an Ada subprogram.

<DT><CODE>adafinal</CODE>
<DD>
<A NAME="IDX192"></A>
You must call this routine to perform any library-level finalization
required by the Ada subprograms. A call to <CODE>adafinal</CODE> is required
after the last call to an Ada subprogram, and before the program
terminates.
</DL>

<P>
If the <CODE>-n</CODE> switch
<A NAME="IDX193"></A>
is given, more than one ALI file may appear on
the command line for <CODE>gnatbind</CODE>. The normal <STRONG>closure</STRONG>
calculation is performed for each of the specified units. Calculating
the closure means finding out the set of units involved by tracing
<CODE>with</CODE> references.  The reason it is necessary to be able to
specify more than one ALI file is that a given program may invoke two or
more quite separate groups of Ada units.

</P>
<P>
The binder takes the name of its output file from the last specified ALI
file, unless overridden by the use of the <CODE>\-o
file\/OUTPUT=file\</CODE>. The output is an Ada unit in source form that can
be compiled with GNAT unless the -C switch is used in which case the
output is a C source file, which must be compiled using the C compiler.
This compilation occurs automatically as part of the <CODE>gnatlink</CODE>
processing.

</P>


<H2><A NAME="SEC59" HREF="gnat_ug_toc.html#TOC59">Binding Programs with no Main Subprogram</A></H2>

<P>
It is possible to have an Ada program which does not have a main
subprogram. This program will call the elaboration routines of all the
packages, then the finalization routines.

</P>
<P>
The following switch is used to bind programs organized in this manner:

</P>
<DL COMPACT>

<DT><CODE>-z</CODE>
<DD>
<A NAME="IDX194"></A>
Normally the binder checks that the unit name given on the command line
corresponds to a suitable main subprogram. When this switch is used,
a list of ALI files can be given, and the execution of the program
consists of elaboration of these units in an appropriate order.
</DL>



<H2><A NAME="SEC60" HREF="gnat_ug_toc.html#TOC60">Summary of Binder Switches</A></H2>

<P>
The following are the switches available with <CODE>gnatbind</CODE>:

</P>
<DL COMPACT>

<DT><CODE>-aO</CODE>
<DD>
Specify directory to be searched for ALI files.

<DT><CODE>-aI</CODE>
<DD>
Specify directory to be searched for source file.

<DT><CODE>-A</CODE>
<DD>
Generate binder program in Ada (default)

<DT><CODE>-b</CODE>
<DD>
Generate brief messages to <CODE>stderr</CODE> even if verbose mode set.

<DT><CODE>-c</CODE>
<DD>
Check only, no generation of binder output file.

<DT><CODE>-C</CODE>
<DD>
Generate binder program in C

<DT><CODE>-e</CODE>
<DD>
Output complete list of elaboration-order dependencies.

<DT><CODE>-E</CODE>
<DD>
Store tracebacks in exception occurrences when the target supports it.
This is the default with the zero cost exception mechanism.
This option is currently only supported on Solaris and Linux where you
explicitly need to use the <CODE>gcc</CODE> flag <CODE>-funwind-tables</CODE> when
compiling every file in your application. See also the packages
<CODE>GNAT.Traceback</CODE> and <CODE>GNAT.Traceback.Symbolic</CODE>

<DT><CODE>-f</CODE>
<DD>
Full elaboration semantics. Follow Ada rules. No attempt to be kind

<DT><CODE>-h</CODE>
<DD>
Output usage (help) information

<DT><CODE>-I</CODE>
<DD>
Specify directory to be searched for source and ALI files.

<DT><CODE>-I-</CODE>
<DD>
Do not look for sources in the current directory where <CODE>gnatbind</CODE> was
invoked, and do not look for ALI files in the directory containing the
ALI file named in the <CODE>gnatbind</CODE> command line.

<DT><CODE>-l</CODE>
<DD>
Output chosen elaboration order.

<DT><CODE>-Mxyz</CODE>
<DD>
Rename generated main program from main to xyz

<DT><CODE>-m<VAR>n</VAR></CODE>
<DD>
Limit number of detected errors to <VAR>n</VAR> (1-999).

<DT><CODE>-n</CODE>
<DD>
No main program.

<DT><CODE>-nostdinc</CODE>
<DD>
Do not look for sources in the system default directory.

<DT><CODE>-nostdlib</CODE>
<DD>
Do not look for library files in the system default directory.

<DT><CODE>-o <VAR>file</VAR></CODE>
<DD>
Name the output file <VAR>file</VAR> (default is <TT>`b~<VAR>xxx</VAR>.adb'</TT>).
Note that if this option is used, then linking must be done manually,
gnatlink cannot be used.

<DT><CODE>-O</CODE>
<DD>
Output object list.

<DT><CODE>-p</CODE>
<DD>
Pessimistic (worst-case) elaboration order

<DT><CODE>-s</CODE>
<DD>
Require all source files to be present.

<DT><CODE>-static</CODE>
<DD>
Link against a static GNAT run time.

<DT><CODE>-shared</CODE>
<DD>
Link against a shared GNAT run time when available.

<DT><CODE>-t</CODE>
<DD>
Tolerate time stamp and other consistency errors

<DT><CODE>-T<VAR>n</VAR></CODE>
<DD>
Set the time slice value to n milliseconds. A value of zero means no time
slicing and also indicates to the tasking run time to match as close as
possible to the annex D requirements of the RM.

<DT><CODE>-v</CODE>
<DD>
Verbose mode. Write error messages, header, summary output to
<CODE>stdout</CODE>.

<DT><CODE>-w<VAR>x</VAR></CODE>
<DD>
Warning mode (<VAR>x</VAR>=s/e for suppress/treat as error)

<DT><CODE>-x</CODE>
<DD>
Exclude source files (check object consistency only).

<DT><CODE>-z</CODE>
<DD>
No main subprogram.

</DL>

<P>
You may obtain this listing by running the program <CODE>gnatbind</CODE> with
no arguments.

</P>


<H2><A NAME="SEC61" HREF="gnat_ug_toc.html#TOC61">Command-Line Access</A></H2>

<P>
The package <CODE>Ada.Command_Line</CODE> provides access to the command-line
arguments and program name. In order for this interface to operate
correctly, the two variables

</P>

<PRE>
   int gnat_argc;
   char **gnat_argv;
</PRE>

<P>
<A NAME="IDX195"></A>
<A NAME="IDX196"></A>
are declared in one of the GNAT library routines. These variables must
be set from the actual <CODE>argc</CODE> and <CODE>argv</CODE> values passed to the
main program.  With no <CODE>n</CODE> present, <CODE>gnatbind</CODE>
generates the C main program to automatically set these variables.
If the <CODE>n</CODE> switch is used, there is no automatic way to
set these variables.  If they are not set, the procedures in
<CODE>Ada.Command_Line</CODE> will not be available, and any attempt to use
them will raise <CODE>Constraint_Error</CODE>. If command line access is
required, your main program must set <CODE>gnat_argc</CODE> and
<CODE>gnat_argv</CODE> from the <CODE>argc</CODE> and <CODE>argv</CODE> values passed to
it.

</P>


<H2><A NAME="SEC62" HREF="gnat_ug_toc.html#TOC62">Search Paths for <CODE>gnatbind</CODE></A></H2>

<P>
The binder takes the name of an ALI file as its argument and needs to
locate source files as well as other ALI files to verify object consistency.

</P>
<P>
For source files, it follows exactly the same search rules as <CODE>gcc</CODE>
(see section <A HREF="gnat_ug.html#SEC49">Search Paths and the Run-Time Library (RTL)</A>). For ALI files the
directories searched are:

</P>

<OL>
<LI>

The directory containing the ALI file named in the command line, unless
the switch <CODE>-I-</CODE> is specified.

<LI>

All directories specified by <CODE>-I</CODE>
switches on the <CODE>gnatbind</CODE>
command line, in the order given.

<LI>

<A NAME="IDX197"></A>
Each of the directories listed in the value of the
<CODE>ADA_OBJECTS_PATH</CODE> environment variable.
Construct this value
exactly as the <CODE>PATH</CODE> environment variable: a list of directory
names separated by colons.

<LI>

The default location for the GNAT Run-Time Library (RTL) files,
determined when GNAT was built and installed on your system, unless
the switch <CODE>-nostdlib</CODE> is specified.
</OL>

<P>
In the binder the switch <CODE>-I</CODE>
is used to specify both source and
library file paths. Use <CODE>-aI</CODE>
instead if you want to specify
source paths only, and <CODE>-aO</CODE>
if you want to specify library paths
only. This means that for the binder
<CODE>-I</CODE><VAR>dir</VAR> is equivalent to
<CODE>-aI</CODE><VAR>dir</VAR>
<CODE>-aO</CODE><VAR>dir</VAR>.
The binder generates the bind file (a C language source file) in the
current working directory.

</P>
<P>
<A NAME="IDX198"></A>
<A NAME="IDX199"></A>
<A NAME="IDX200"></A>
<A NAME="IDX201"></A>
The packages <CODE>Ada</CODE>, <CODE>System</CODE>, and <CODE>Interfaces</CODE> and their
children make up the GNAT Run-Time Library, together with the package
GNAT and its children, which contain a set of useful additional
library functions provided by GNAT. The sources for these units are
needed by the compiler and are kept together in one directory. The ALI
files and object files generated by compiling the RTL are needed by the
binder and the linker and are kept together in one directory, typically
different from the directory containing the sources. In a normal
installation, you need not specify these directory names when compiling
or binding.  Either the environment variables or the built-in defaults
cause these files to be found.

</P>
<P>
Besides simplifying access to the RTL, a major use of search paths is
in compiling sources from multiple directories. This can make
development environments much more flexible.

</P>


<H2><A NAME="SEC63" HREF="gnat_ug_toc.html#TOC63">Examples of <CODE>gnatbind</CODE> Usage</A></H2>

<P>
This section contains a number of examples of using the GNAT binding
utility <CODE>gnatbind</CODE>.

</P>
<DL COMPACT>

<DT><CODE>gnatbind hello</CODE>
<DD>
The main program <CODE>Hello</CODE> (source program in <TT>`hello.adb'</TT>) is
bound using the standard switch settings. The generated main program is
<TT>`b~hello.adb'</TT>. This is the normal, default use of the binder.

<DT><CODE>gnatbind hello -o mainprog.adb</CODE>
<DD>
The main program <CODE>Hello</CODE> (source program in <TT>`hello.adb'</TT>) is
bound using the standard switch settings. The generated main program is
<TT>`mainprog.adb'</TT> with the associated spec in
<TT>`mainprog.ads'</TT>. Note that you must specify the body here not the
spec, in the case where the output is in Ada. Note that if this option
is used, then linking must be done manually, since gnatlink will not
be able to find the generated file.

<DT><CODE>gnatbind main -C -o mainprog.c -x</CODE>
<DD>
The main program <CODE>Main</CODE> (source program in
<TT>`main.adb'</TT>) is bound, excluding source files from the
consistency checking, generating
the file <TT>`mainprog.c'</TT>.

<DT><CODE>gnatbind -x main_program -C -o mainprog.c</CODE>
<DD>
This command is exactly the same as the previous example. Switches may
appear anywhere in the command line, and single letter switches may be
combined into a single switch.

<DT><CODE>gnatbind -n math dbase -C -o ada-control.c</CODE>
<DD>
The main program is in a language other than Ada, but calls to
subprograms in packages <CODE>Math</CODE> and <CODE>Dbase</CODE> appear. This call
to <CODE>gnatbind</CODE> generates the file <TT>`ada-control.c'</TT> containing
the <CODE>adainit</CODE> and <CODE>adafinal</CODE> routines to be called before and
after accessing the Ada units.
</DL>



<H1><A NAME="SEC64" HREF="gnat_ug_toc.html#TOC64">Linking Using <CODE>gnatlink</CODE></A></H1>
<P>
<A NAME="IDX202"></A>

</P>
<P>
This chapter discusses <CODE>gnatlink</CODE>, a utility program used to link
Ada programs and build an executable file. This is a simple program
that invokes the UNIX linker (via the <CODE>gcc</CODE>
command) with a correct list of object files and library references.
<CODE>gnatlink</CODE> automatically determines the list of files and
references for the Ada part of a program. It uses the binder file
generated by the binder to determine this list.

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC65">Running gnatlink</A>
<LI><A HREF="gnat_ug.html#SEC66">Switches for gnatlink</A>
</UL>



<H2><A NAME="SEC65" HREF="gnat_ug_toc.html#TOC65">Running <CODE>gnatlink</CODE></A></H2>

<P>
The form of the <CODE>gnatlink</CODE> command is

</P>

<PRE>
   $ gnatlink [<VAR>switches</VAR>] <VAR>mainprog</VAR>[.ali] [<VAR>non-Ada objects</VAR>] [<VAR>linker options</VAR>]
</PRE>

<P>
<TT>`<VAR>mainprog</VAR>.ali'</TT> references the ALI file of the main program.
The <TT>`.ali'</TT> extension of this file can be omitted. From this
reference, <CODE>gnatlink</CODE> locates the corresponding binder file
<TT>`b~<VAR>mainprog</VAR>.adb'</TT> and, using the information in this file along
with the list of non-Ada objects and linker options, constructs a UNIX
linker command file to create the executable.

</P>
<P>
The arguments following <TT>`<VAR>mainprog</VAR>.ali'</TT> are passed to the
linker uninterpreted. They typically include the names of object files
for units written in other languages than Ada and any library references
required to resolve references in any of these foreign language units,
or in <CODE>pragma Import</CODE> statements in any Ada units.  This list may
also include linker switches.

</P>
<P>
<CODE>gnatlink</CODE> determines the list of objects required by the Ada
program and prepends them to the list of objects passed to the linker.
<CODE>gnatlink</CODE> also gathers any arguments set by the use of
<CODE>pragma Linker_Options</CODE> and adds them to the list of arguments
presented to the linker.

</P>



<H2><A NAME="SEC66" HREF="gnat_ug_toc.html#TOC66">Switches for <CODE>gnatlink</CODE></A></H2>

<P>
The following switches are available with the <CODE>gnatlink</CODE> utility:

</P>
<DL COMPACT>

<DT><CODE>-A</CODE>
<DD>
<A NAME="IDX203"></A>
The binder has generated code in Ada. This is the default.

<DT><CODE>-C</CODE>
<DD>
<A NAME="IDX204"></A>
If instead of generating a file in Ada, the binder has generated one in
C, then the linker needs to know about it. Use this switch to signal
to <CODE>gnatlink</CODE> that the binder has generated C code rather than
Ada code.

<DT><CODE>-g</CODE>
<DD>
<A NAME="IDX205"></A>
<A NAME="IDX206"></A>
The option to include debugging information causes the Ada bind file (in
other words, <TT>`b~<VAR>mainprog</VAR>.adb'</TT>) to be compiled with
<CODE>-g</CODE>.
In addition, the binder does not delete the <TT>`b~<VAR>mainprog</VAR>.adb'</TT>,
<TT>`b~<VAR>mainprog</VAR>.o'</TT> and <TT>`b~<VAR>mainprog</VAR>.ali'</TT> files.
Without <CODE>-g</CODE>, the binder removes these files by
default. The same procedure apply if a C bind file was generated using
<CODE>-C</CODE> <CODE>gnatbind</CODE> option, in this case the filenames are
<TT>`b_<VAR>mainprog</VAR>.c'</TT> and <TT>`b_<VAR>mainprog</VAR>.o'</TT>.

<DT><CODE>-n</CODE>
<DD>
<A NAME="IDX207"></A>
Do not compile the file generated by the binder. This may be used when
a link is rerun with different options, but there is no need to recompile
the binder file.

<DT><CODE>-v</CODE>
<DD>
<A NAME="IDX208"></A>
Causes additional information to be output, including a full list of the
included object files. This switch option is most useful when you want
to see what set of object files are being used in the link step.

<DT><CODE>-v -v</CODE>
<DD>
<A NAME="IDX209"></A>
Very verbose mode. Requests that the compiler operate in verbose mode when
it compiles the binder file, and that the system linker run in verbose mode.

<DT><CODE>-o <VAR>exec-name</VAR></CODE>
<DD>
<A NAME="IDX210"></A>
<VAR>exec-name</VAR> specifies an alternate name for the generated
executable program. If this switch is omitted, the executable has the same
name as the main unit. For example, <CODE>gnatlink try.ali</CODE> creates
an executable called <TT>`try'</TT>.

<DT><CODE>-b <VAR>target</VAR></CODE>
<DD>
<A NAME="IDX211"></A>
Compile your program to run on <VAR>target</VAR>, which is the name of a
system configuration.  You must have a GNAT cross-compiler built if
<VAR>target</VAR> is not the same as your host system.

<DT><CODE>-B<VAR>dir</VAR></CODE>
<DD>
<A NAME="IDX212"></A>
Load compiler executables (for example, <CODE>gnat1</CODE>, the Ada compiler)
from <VAR>dir</VAR> instead of the default location. Only use this switch
when multiple versions of the GNAT compiler are available. See the
<CODE>gcc</CODE> manual page for further details.  You would normally use the
<CODE>-b</CODE> or <CODE>-V</CODE> switch instead.

<DT><CODE>--GCC=<VAR>compiler_name</VAR></CODE>
<DD>
<A NAME="IDX213"></A>
Program used for compiling the binder file. The default is
<CODE>gcc</CODE>'. You need to use quotes around <VAR>compiler_name</VAR> if
<CODE>compiler_name</CODE> contains spaces or other separator characters. As
an example <CODE>--GCC="foo -x -y"</CODE> will instruct <CODE>gnatlink</CODE> to use
<CODE>foo -x -y</CODE> as your compiler.  Note that switch <CODE>-c</CODE> is always
inserted after your command name. Thus in the above example the compiler
command that will be used by <CODE>gnatlink</CODE> will be <CODE>foo -c -x -y</CODE>.

<DT><CODE>--LINK=<VAR>name</VAR></CODE>
<DD>
<A NAME="IDX214"></A>
<VAR>name</VAR> is the name of the linker to be invoked. This is especially
useful in mixed language programs since languages such as c++ require
their own linker to be used. When this switch is
omitted, the default name for the linker is (<TT>`gcc'</TT>).

</DL>



<H1><A NAME="SEC67" HREF="gnat_ug_toc.html#TOC67">The GNAT Make Program <CODE>gnatmake</CODE></A></H1>
<P>
<A NAME="IDX215"></A>

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC68">Running gnatmake</A>
<LI><A HREF="gnat_ug.html#SEC69">Switches for gnatmake</A>
<LI><A HREF="gnat_ug.html#SEC70">Mode switches for gnatmake</A>
<LI><A HREF="gnat_ug.html#SEC71">Notes on the Command Line</A>
<LI><A HREF="gnat_ug.html#SEC72">How gnatmake Works</A>
<LI><A HREF="gnat_ug.html#SEC73">Examples of gnatmake Usage</A>
<LI><A HREF="gnat_ug.html#SEC74">Gnatmake in makefiles</A>
</UL>
<P>
A typical development cycle when working on an Ada program consists of
the following steps:

</P>

<OL>
<LI>

Edit some sources to fix bugs.

<LI>

Add enhancements.

<LI>

Compile all sources affected.

<LI>

Rebind and relink.

<LI>

Test.
</OL>

<P>
The third step can be tricky, because not only do the modified files
<A NAME="IDX216"></A>
have to be compiled, but any files depending on these files must also be
recompiled. The dependency rules in Ada can be quite complex, especially
in the presence of overloading, <CODE>use</CODE> clauses, generics and inlined
subprograms.

</P>
<P>
<CODE>gnatmake</CODE> automatically takes care of the third and fourth steps
of this process. It determines which sources need to be compiled,
compiles them, and binds and links the resulting object files.

</P>
<P>
Unlike some other Ada make programs, the dependencies are always
accurately recomputed from the new sources. The source based approach of
the GNAT compilation model makes this possible. This means that if
changes to the source program cause corresponding changes in
dependencies, they will always be tracked exactly correctly by
<CODE>gnatmake</CODE>.

</P>


<H2><A NAME="SEC68" HREF="gnat_ug_toc.html#TOC68">Running <CODE>gnatmake</CODE></A></H2>

<P>
The form of the <CODE>gnatmake</CODE> command is

</P>

<PRE>
   $ gnatmake [<VAR>switches</VAR>] <VAR>file_name</VAR> [<VAR>mode_switches</VAR>]
</PRE>

<P>
The only required argument is <VAR>file_name</VAR>, which specifies
the compilation unit that is the main program.  If <CODE>switches</CODE> are
present, they can be placed before of after <VAR>file_name</VAR>.
If <VAR>mode_switches</VAR> are present, they must always be placed after
<VAR>file_name</VAR> and all <CODE>switches</CODE>.

</P>
<P>
If you are using standard file extensions (.adb and .ads), then the
extension may be omitted from the <VAR>file_name</VAR> argument. However, if
you are using non-standard extensions, then it is required that the
extension be given. A relative or absolute directory path can be
specified in <VAR>file_name</VAR>, in which case, the input source file will
be searched for in the specified directory only. Otherwise, the input
source file will first be searched in the directory where
<CODE>gnatmake</CODE> was invoked and if it is not found, it will be search on
the source path of the compiler as described in section <A HREF="gnat_ug.html#SEC49">Search Paths and the Run-Time Library (RTL)</A>.

</P>
<P>
All <CODE>gnatmake</CODE> output (except when you specify
<CODE>-M</CODE>) is to
<CODE>stderr</CODE>. The output produced by the
<CODE>-M</CODE> switch is send to
<CODE>stdout</CODE>.

</P>


<H2><A NAME="SEC69" HREF="gnat_ug_toc.html#TOC69">Switches for <CODE>gnatmake</CODE></A></H2>

<P>
You may specify any of the following switches to <CODE>gnatmake</CODE>:

</P>
<DL COMPACT>

<DT><CODE>--GCC=<VAR>compiler_name</VAR></CODE>
<DD>
<A NAME="IDX217"></A>
Program used for compiling. The default is <CODE>gcc</CODE>'. You need to use
quotes around <VAR>compiler_name</VAR> if <CODE>compiler_name</CODE> contains
spaces or other separator characters. As an example <CODE>--GCC="foo -x
-y"</CODE> will instruct <CODE>gnatmake</CODE> to use <CODE>foo -x -y</CODE> as your
compiler.  Note that switch <CODE>-c</CODE> is always inserted after your
command name. Thus in the above example the compiler command that will
be used by <CODE>gnatmake</CODE> will be <CODE>foo -c -x -y</CODE>.

<DT><CODE>--GNATBIND=<VAR>binder_name</VAR></CODE>
<DD>
<A NAME="IDX218"></A>
Program used for binding. The default is <CODE>gnatbind</CODE>'. You need to
use quotes around <VAR>binder_name</VAR> if <VAR>binder_name</VAR> contains spaces
or other separator characters.  As an example <CODE>--GNATBIND="bar -x
-y"</CODE> will instruct <CODE>gnatmake</CODE> to use <CODE>bar -x -y</CODE> as your
binder. Binder switches that are normally appended by <CODE>gnatmake</CODE> to
<CODE>gnatbind</CODE>' are now appended to the end of <CODE>bar -x -y</CODE>.

<DT><CODE>--GNATLINK=<VAR>linker_name</VAR></CODE>
<DD>
<A NAME="IDX219"></A>
Program used for linking. The default is <CODE>gnatlink</CODE>'. You need to
use quotes around <VAR>linker_name</VAR> if <VAR>linker_name</VAR> contains spaces
or other separator characters.  As an example <CODE>--GNATLINK="lan -x
-y"</CODE> will instruct <CODE>gnatmake</CODE> to use <CODE>lan -x -y</CODE> as your
linker. Linker switches that are normally appended by <CODE>gnatmake</CODE> to
<CODE>gnatlink</CODE>' are now appended to the end of <CODE>lan -x -y</CODE>.

<DT><CODE>-a</CODE>
<DD>
<A NAME="IDX220"></A>
Consider all files in the make process, even the GNAT internal system
files (for example, the predefined Ada library files), as well as any
locked files. Locked files are files whose ALI file is write-protected.
By default,
<CODE>gnatmake</CODE> does not check these files,
because the assumption is that the GNAT internal files are properly up
to date, and also that any write protected ALI files have been properly
installed. Note that if there is an installation problem, such that one
of these files is not up to date, it will be properly caught by the
binder.
You may have to specify this switch if you are working on GNAT
itself. <CODE>-f</CODE> is also useful in conjunction with
<CODE>-f</CODE>
if you need to recompile an entire application,
including run-time files, using special configuration pragma settings,
such as a non-standard <CODE>Float_Representation</CODE> pragma.
By default
<CODE>gnatmake -a</CODE> compiles all GNAT
internal files with
<CODE>gcc -c -gnatg</CODE> rather than <CODE>gcc -c</CODE>.

<DT><CODE>-c</CODE>
<DD>
<A NAME="IDX221"></A>
Compile only. Do not perform binding and linking. If the root unit
specified by <VAR>file_name</VAR> is not a main unit, this is the
default.  Otherwise <CODE>gnatmake</CODE> will attempt binding and linking
unless all objects are up to date and the executable is more recent than
the objects.

<DT><CODE>-f</CODE>
<DD>
<A NAME="IDX222"></A>
Force recompilations. Recompile all sources, even though some object
files may be up to date, but don't recompile predefined or GNAT internal
files or locked files (files with a write-protected ALI file),
unless the <CODE>-a</CODE> switch is also specified.

<DT><CODE></CODE>
<DD>
<DT><CODE>-i</CODE>
<DD>
<A NAME="IDX223"></A>
In normal mode, <CODE>gnatmake</CODE> compiles all object files and ALI files
into the current directory. If the <CODE>-i</CODE> switch is used,
then instead object files and ALI files that already exist are overwritten
in place. This means that once a large project is organized into separate
directories in the desired manner, then <CODE>gnatmake</CODE> will automatically
maintain and update this organization. If no ALI files are found on the
Ada object path (section <A HREF="gnat_ug.html#SEC49">Search Paths and the Run-Time Library (RTL)</A>),
the new object and ALI files are created in the
directory containing the source being compiled. If another organization
is desired, where objects and sources are kept in different directories,
a useful technique is to create dummy ALI files in the desired directories.
When detecting such a dummy file, <CODE>gnatmake</CODE> will be forced to recompile
the corresponding source file, and it will be put the resulting object
and ALI files in the directory where it found the dummy file.

<DT><CODE>-j<VAR>n</VAR></CODE>
<DD>
<A NAME="IDX224"></A>
<A NAME="IDX225"></A>
Use <VAR>n</VAR> processes to carry out the (re)compilations. On a
multiprocessor machine compilations will occur in parallel.  In the
event of compilation errors, messages from various compilations might
get interspersed (but <CODE>gnatmake</CODE> will give you the full ordered
list of failing compiles at the end). If this is problematic, rerun
the make process with n set to 1 to get a clean list of messages.

<DT><CODE>-k</CODE>
<DD>
<A NAME="IDX226"></A>
Keep going. Continue as much as possible after a compilation error.  To
ease the programmer's task in case of compilation errors, the list of
sources for which the compile fails is given when <CODE>gnatmake</CODE>
terminates.

<DT><CODE>-m</CODE>
<DD>
<A NAME="IDX227"></A>
Specifies that the minimum necessary amount of recompilations
be performed. In this mode <CODE>gnatmake</CODE> ignores time
stamp differences when the only
modifications to a source file consist in adding/removing comments,
empty lines, spaces or tabs. This means that if you have changed the
comments in a source file or have simply reformatted it, using this
switch will tell gnatmake not to recompile files that depend on it
(provided other sources on which these files depend have undergone no
semantic modifications).

<DT><CODE>-M</CODE>
<DD>
<A NAME="IDX228"></A>
<A NAME="IDX229"></A>
Check if all objects are up to date. If they are, output the object
dependences to <CODE>stdout</CODE> in a form that can be directly exploited in
a <TT>`Makefile'</TT>. By default, each source file is prefixed with its
(relative or absolute) directory name. This name is whatever you
specified in the various <CODE>-aI</CODE>
and <CODE>-I</CODE> switches.  If you use
<CODE>gnatmake -M</CODE>
<CODE>-q</CODE>
(see below), only the source file names,
without relative paths, are output. If you just specify the
<CODE>-M</CODE>
switch, dependencies of the GNAT internal system files are omitted. This
is typically what you want. If you also specify
the <CODE>-a</CODE> switch,
dependencies of the GNAT internal files are also listed. Note that
dependencies of the objects in external Ada libraries (see switch
<CODE>-aL</CODE><VAR>dir</VAR> in the following list) are never reported.

<DT><CODE>-n</CODE>
<DD>
<A NAME="IDX230"></A>
Don't compile, bind, or link.  Checks if all objects are up to date.
If they are not, the full name of the first file that needs to be
recompiled is printed.
Repeated use of this option, followed by compiling the indicated source
file, will eventually result in recompiling all required units.

<DT><CODE>-o <VAR>exec_name</VAR></CODE>
<DD>
<A NAME="IDX231"></A>
Output executable name. The name of the final executable program will be
<VAR>exec_name</VAR>. If the <CODE>-o</CODE> switch is omitted the default
name for the executable will be the name of the input file in appropriate form
for an executable file on the host system.

<DT><CODE>-q</CODE>
<DD>
<A NAME="IDX232"></A>
Quiet. When this flag is not set, the commands carried out by
<CODE>gnatmake</CODE> are displayed.

<DT><CODE>-v</CODE>
<DD>
<A NAME="IDX233"></A>
Verbose. Displays the reason for all recompilations <CODE>gnatmake</CODE>
decides are necessary.

<DT><CODE>-z</CODE>
<DD>
<A NAME="IDX234"></A>
No main subprogram. Bind and link the program even if the unit name
given on the command line is a package name. The resulting executable
will execute the elaboration routines of the package and its closure,
then the finalization routines.

<DT><CODE><CODE>gcc</CODE> switches</CODE>
<DD>
The switch <CODE>-g</CODE> or any uppercase switch (other than <CODE>-A</CODE>, or
<CODE>-L</CODE>) or any switch that is more than one character is passed to
<CODE>gcc</CODE> (e.g. <CODE>-O</CODE>, <CODE>-gnato,</CODE> etc.)
</DL>

<P>
Source and library search path switches:

</P>
<DL COMPACT>

<DT><CODE>-aI<VAR>dir</VAR></CODE>
<DD>
<A NAME="IDX235"></A>
When looking for source files also look in directory <VAR>dir</VAR>.
The order in which source files search is undertaken is
described in section <A HREF="gnat_ug.html#SEC49">Search Paths and the Run-Time Library (RTL)</A>.

<DT><CODE>-aL<VAR>dir</VAR></CODE>
<DD>
<A NAME="IDX236"></A>
Consider <VAR>dir</VAR> as being an externally provided Ada library.
Instructs <CODE>gnatmake</CODE> to skip compilation units whose <TT>`.ali'</TT>
files have been located in directory <VAR>dir</VAR>. This allows you to have
missing bodies for the units in <VAR>dir</VAR>.  You still need to specify
the location of the specs for these units by using the switches
<CODE>-aI<VAR>dir</VAR></CODE>
or <CODE>-I<VAR>dir</VAR></CODE>.
Note: this switch is provided for compatibility with previous versions
of <CODE>gnatmake</CODE>. The easier method of causing standard libraries
to be excluded from consideration is to write-protect the corresponding
ALI files.

<DT><CODE>-aO<VAR>dir</VAR></CODE>
<DD>
<A NAME="IDX237"></A>
When searching for library and object files, look in directory
<VAR>dir</VAR>. The order in which library files are searched is described in
section <A HREF="gnat_ug.html#SEC62">Search Paths for <CODE>gnatbind</CODE></A>.

<DT><CODE>-A<VAR>dir</VAR></CODE>
<DD>
<A NAME="IDX238"></A>
<A NAME="IDX239"></A>
Equivalent to <CODE>-aL<VAR>dir</VAR>
-aI<VAR>dir</VAR></CODE>.

<DT><CODE>-I<VAR>dir</VAR></CODE>
<DD>
<A NAME="IDX240"></A>
Equivalent to <CODE>-aO<VAR>dir</VAR>
-aI<VAR>dir</VAR></CODE>.

<DT><CODE>-I-</CODE>
<DD>
<A NAME="IDX241"></A>
<A NAME="IDX242"></A>
Do not look for source files in the directory containing the source
file named in the command line.
Do not look for ALI or object files in the directory
where <CODE>gnatmake</CODE> was invoked.

<DT><CODE>-L<VAR>dir</VAR></CODE>
<DD>
<A NAME="IDX243"></A>
<A NAME="IDX244"></A>
Add directory <VAR>dir</VAR> to the list of directories in which the linker
will search for libraries. This is equivalent to
<CODE>-largs -L</CODE><VAR>dir</VAR>.

<DT><CODE>-nostdinc</CODE>
<DD>
<A NAME="IDX245"></A>
Do not look for source files in the system default directory.

<DT><CODE>-nostdlib</CODE>
<DD>
<A NAME="IDX246"></A>
Do not look for library files in the system default directory.
</DL>



<H2><A NAME="SEC70" HREF="gnat_ug_toc.html#TOC70">Mode switches for <CODE>gnatmake</CODE></A></H2>

<P>
The mode switches (referred to as <CODE>mode_switches</CODE>) allow the
inclusion of switches that are to be passed to the compiler itself, the
binder or the linker. The effect of a mode switch is to cause all
subsequent switches up to the end of the switch list, or up to the next
mode switch, to be interpreted as switches to be passed on to the
designated component of GNAT.

</P>
<DL COMPACT>

<DT><CODE>-cargs <VAR>switches</VAR></CODE>
<DD>
<A NAME="IDX247"></A>
Compiler switches. Here <VAR>switches</VAR> is a list of switches
that are valid switches for <CODE>gcc</CODE>. They will be passed on to
all compile steps performed by <CODE>gnatmake</CODE>.

<DT><CODE>-bargs <VAR>switches</VAR></CODE>
<DD>
<A NAME="IDX248"></A>
Binder switches. Here <VAR>switches</VAR> is a list of switches
that are valid switches for <CODE>gcc</CODE>. They will be passed on to
all bind steps performed by <CODE>gnatmake</CODE>.

<DT><CODE>-largs <VAR>switches</VAR></CODE>
<DD>
<A NAME="IDX249"></A>
Linker switches. Here <VAR>switches</VAR> is a list of switches
that are valid switches for <CODE>gcc</CODE>. They will be passed on to
all link steps performed by <CODE>gnatmake</CODE>.
</DL>



<H2><A NAME="SEC71" HREF="gnat_ug_toc.html#TOC71">Notes on the Command Line</A></H2>

<P>
This section contains some additional useful notes on the operation
of the <CODE>gnatmake</CODE> command.

</P>

<UL>
<LI>

<A NAME="IDX250"></A>
If <CODE>gnatmake</CODE> finds no ALI files, it recompiles the main program
and all other units required by the main program.
This means that <CODE>gnatmake</CODE>
can be used for the initial compile, as well as during subsequent steps of
the development cycle.

<LI>

If you enter <CODE>gnatmake <VAR>file</VAR>.adb</CODE>, where <TT>`<VAR>file</VAR>.adb'</TT>
is a subunit or body of a generic unit, <CODE>gnatmake</CODE> recompiles
<TT>`<VAR>file</VAR>.adb'</TT> (because it finds no ALI) and stops, issuing a
warning.

<LI>

In <CODE>gnatmake</CODE> the switch <CODE>-I</CODE>
is used to specify both source and
library file paths. Use <CODE>-aI</CODE>
instead if you just want to specify
source paths only and <CODE>-aO</CODE>
if you want to specify library paths
only.

<LI>

<CODE>gnatmake</CODE> examines both an ALI file and its corresponding object file
for consistency. If an ALI is more recent than its corresponding object,
or if the object file is missing, the corresponding source will be recompiled.
Note that <CODE>gnatmake</CODE> expects an ALI and the corresponding object file
to be in the same directory.

<LI>

<CODE>gnatmake</CODE> will ignore any files whose ALI file is write-protected.
This may conveniently be used to exclude standard libraries from
consideration and in particular it means that the use of the
<CODE>-f</CODE> switch will not recompile these files
unless <CODE>-a</CODE> is also specified.

<LI>

<CODE>gnatmake</CODE> has been designed to make the use of Ada libraries
particularly convenient. Assume you have an Ada library organized
as follows: <VAR>obj-dir</VAR> contains the objects and ALI files for
of your Ada compilation units,
whereas <VAR>include-dir</VAR> contains the
specs of these units, but no bodies. Then to compile a unit
stored in <CODE>main.adb</CODE>, which uses this Ada library you would just type


<PRE>
   $ gnatmake -aI<VAR>include-dir</VAR>  -aL<VAR>obj-dir</VAR>  main
</PRE>

<LI>

Using <CODE>gnatmake</CODE> along with the
<CODE>-m (minimal recompilation)</CODE>
switch provides an
extremely powerful tool: you can freely update the comments/format of your
source files without having to recompile everything. Note, however, that
adding or deleting lines in a source files may render its debugging
info obsolete. If the file in question is a spec, the impact is rather
limited, as that debugging info will only be useful during the
elaboration phase of your program. For bodies the impact can be more
significant. In all events, your debugger will warn you if a source file
is more recent than the corresponding object, and therefore obsolescence of
debugging information will go unnoticed.
</UL>



<H2><A NAME="SEC72" HREF="gnat_ug_toc.html#TOC72">How <CODE>gnatmake</CODE> Works</A></H2>

<P>
Generally <CODE>gnatmake</CODE> automatically performs all necessary
recompilations and you don't need to worry about how it works. However,
it may be useful to have some basic understanding of the <CODE>gnatmake</CODE>
approach and in particular to understand how it uses the results of
previous compilations without incorrectly depending on them.

</P>
<P>
First a definition: an object file is considered <STRONG>up to date</STRONG> if the
corresponding ALI file exists and its time stamp predates that of the
object file and if all the source files listed in the
dependency section of this ALI file have time stamps matching those in
the ALI file. This means that neither the source file itself nor any
files that it depends on have been modified, and hence there is no need
to recompile this file.

</P>
<P>
<CODE>gnatmake</CODE> works by first checking if the specified main unit is up
to date. If so, no compilations are required for the main unit.  If not,
<CODE>gnatmake</CODE> compiles the main program to build a new ALI file that
reflects the latest sources. Then the ALI file of the main unit is
examined to find all the source files on which the main program depends,
and <CODE>gnatmake</CODE> recursively applies the above procedure on all these files.

</P>
<P>
This process ensures that <CODE>gnatmake</CODE> only trusts the dependencies
in an existing ALI file if they are known to be correct.  Otherwise it
always recompiles to determine a new, guaranteed accurate set of
dependencies. As a result the program is compiled "upside down" from what may
be more familiar as the required order of compilation in some other Ada
systems. In particular, clients are compiled before the units on which
they depend. The ability of GNAT to compile in any order is critical in
allowing an order of compilation to be chosen that guarantees that
<CODE>gnatmake</CODE> will recompute a correct set of new dependencies if
necessary.

</P>


<H2><A NAME="SEC73" HREF="gnat_ug_toc.html#TOC73">Examples of <CODE>gnatmake</CODE> Usage</A></H2>

<DL COMPACT>

<DT><CODE>gnatmake hello.adb</CODE>
<DD>
Compile all files necessary to bind and link the main program
<TT>`hello.adb'</TT> (containing unit <CODE>Hello</CODE>) and bind and link the
resulting object files to generate an executable file <TT>`hello'</TT>.

<DT><CODE>gnatmake -q Main_Unit -cargs -O2 -bargs -l</CODE>
<DD>
Compile all files necessary to bind and link the main program unit
<CODE>Main_Unit</CODE> (from file <TT>`main_unit.adb'</TT>). All compilations will
be done with optimization level 2 and the order of elaboration will be
listed by the binder. <CODE>gnatmake</CODE> will operate in quiet mode, not
displaying commands it is executing.
</DL>



<H2><A NAME="SEC74" HREF="gnat_ug_toc.html#TOC74">Gnatmake in makefiles</A></H2>
<P>
<A NAME="IDX251"></A>
<A NAME="IDX252"></A>

</P>
<P>
Complex project organizations can be handled in a very powerful way by
using GNU make combined with gnatmake. Here is for instance a Makefile
which allows to build each subsystem of a big project into a separate
shared library. Such a makefile allows to significantly reduce the link
time of very bug applications while maintaining a complete coherence at
each step of the build process.

</P>

<PRE>
## This Makefile is intended to be used with the following directory
## configuration:
##  - The sources are split into a series of csc (computer software components)
##    Each of these csc is put in its own directory.
##    Their name are referenced by the directory names.
##    They will be compiled into shared library (although this would also work
##    with static libraries
##  - The main program (and possibly other packages that do not belong to any
##    csc is put in the top level directory (where the Makefile is).
##       toplevel_dir __ first_csc  (sources) __ lib (will contain the library)
##                    \_ second_csc (sources) __ lib (will contain the library)
##                    \_ ...
## Although this Makefile is build for shared library, it is easy to modify
## to build partial link objects instead (modify the lines with -shared and
## gnatlink below)
##
## With this makefile, you can change any file in the system or add any new
## file, and everything will be recompiled correctly (only the relevant shared
## objects will be recompiled, and the main program will be re-linked).

# The list of computer software component for your project
CSC_LIST=aa bb cc

# Name of the main program (no extension)
MAIN=main

# If we need to build objects with -fPIC, uncomment the following line
#NEED_FPIC=-fPIC

# The following variable should give the directory containing libgnat.so
# You can get this directory through 'gnatls -v'. This is usually the last
# directory in the Object_Path.
GLIB=...

# The directories for the libraries
# (This macro expands the list of CSC to the list of shared libraries, you
# could simply use the expanded form :
# LIB_DIR=aa/lib/libaa.so bb/lib/libbb.so cc/lib/libcc.so
LIB_DIR=${foreach dir,${CSC_LIST},${dir}/lib/lib${dir}.so}

${MAIN}: objects ${LIB_DIR}
	gnatbind ${MAIN} ${CSC_LIST:%=-aO%/lib} -shared
	gnatlink ${MAIN} ${CSC_LIST:%=-l%}

objects::
	# recompile the sources
	gnatmake -c -i ${MAIN}.adb ${NEED_FPIC} ${CSC_LIST:%=-I%}

# Note about the rules below: if your csc are not split into multiple
# directories, but simply by their name, you need to replace *.o and
# *.ali with the appropriate list of files
# Note: In a future version of GNAT, the following commands will be simplified
# by a new tool, gnatmlib
${LIB_DIR}:
	mkdir -p ${dir $ }
	cd ${dir $ }; gcc -shared -o ${notdir $ } ../*.o -L${GLIB} -lgnat
	cd ${dir $ }; cp -f ../*.ali .

# The dependencies for the modules
aa/lib/libaa.so: aa/*.o
bb/lib/libbb.so: bb/*.o
bb/lib/libcc.so: cc/*.o

run::
	LD_LIBRARY_PATH=pwd/aa/lib:pwd/bb/lib:pwd/cc/lib ./${MAIN}

clean::
	${RM} -rf ${CSC_LIST:%=%/lib}
	${RM} ${CSC_LIST:%=%/*.ali}
	${RM} ${CSC_LIST:%=%/*.o}
	${RM} *.o *.ali ${MAIN}

</PRE>



<H1><A NAME="SEC75" HREF="gnat_ug_toc.html#TOC75">Renaming Files Using <CODE>gnatchop</CODE></A></H1>
<P>
<A NAME="IDX253"></A>

</P>
<P>
This chapter discusses how to handle files with multiple units by using
the <CODE>gnatchop</CODE> utility. This utility is also useful in renaming
files to meet the standard GNAT default file naming conventions.

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC76">Handling Files with Multiple Units</A>
<LI><A HREF="gnat_ug.html#SEC77">Operating gnatchop in Compilation Mode</A>
<LI><A HREF="gnat_ug.html#SEC78">Command Line for gnatchop</A>
<LI><A HREF="gnat_ug.html#SEC79">Switches for gnatchop</A>
<LI><A HREF="gnat_ug.html#SEC80">Examples of gnatchop Usage</A>
</UL>



<H2><A NAME="SEC76" HREF="gnat_ug_toc.html#TOC76">Handling Files with Multiple Units</A></H2>

<P>
The basic compilation model of GNAT requires that a file submitted to the
compiler have only one unit and there be a strict correspondence
between the file name and the unit name.

</P>
<P>
The <CODE>gnatchop</CODE> utility allows both of these rules to be relaxed,
allowing GNAT to process files which contain multiple compilation units
and files with arbitrary file names. <CODE>gnatchop</CODE>
reads the specified file and generates one or more output files,
containing one unit per file. The unit and the file name correspond,
as required by GNAT.

</P>
<P>
If you want to permanently restructure a set of "foreign" files so that
they match the GNAT rules, and do the remaining development using the
GNAT structure, you can simply use <CODE>gnatchop</CODE> once, generate the
new set of files and work with them from that point on.

</P>
<P>
Alternatively, if you want to keep your files in the "foreign" format,
perhaps to maintain compatibility with some other Ada compilation
system, you can set up a procedure where you use <CODE>gnatchop</CODE> each
time you compile, regarding the source files that it writes as temporary
files that you throw away.

</P>


<H2><A NAME="SEC77" HREF="gnat_ug_toc.html#TOC77">Operating gnatchop in Compilation Mode</A></H2>

<P>
The basic function of <CODE>gnatchop</CODE> is to take a file with multiple units
and split it into separate files. The boundary between files is reasonably
clear, except for the issue of comments and pragmas. In default mode, the
rule is that any pragmas between units belong to the previous unit, except
that configuration pragmas always belong to the following unit. Any comments
belong to the following unit. These rules
almost always result in the right choice of
the split point without needing to mark it explicitly and most users will
find this default to be what they want. In this default mode it is incorrect to
submit a file containing only configuration pragmas, or one that ends in
configuration pragmas, to <CODE>gnatchop</CODE>.

</P>
<P>
However, using a special option to activate "compilation mode",
<CODE>gnatchop</CODE>
can perform another function, which is to provide exactly the semantics
required by the RM for handling of configuration pragmas in a compilation.
In the absence of configuration pragmas (at the main file level), this
option has no effect, but it causes such configuration pragmas to be handled
in a quite different manner.

</P>
<P>
First, in compilation mode, if <CODE>gnatchop</CODE> is given a file that consists of
only configuration pragmas, then this file is appended to the
<TT>`gnat.adc'</TT> file in the current directory. This behavior provides
the required behavior described in the RM for the actions to be taken
on submitting such a file to the compiler, namely that these pragmas
should apply to all subsequent compilations in the same compilation
environment. Using GNAT, the current directory, possibly containing a
<TT>`gnat.adc'</TT> file is the representation
of a compilation environment. For more information on the
<TT>`gnat.adc'</TT> file, see the section on handling of configuration
pragmas see section <A HREF="gnat_ug.html#SEC82">Handling of Configuration Pragmas</A>.

</P>
<P>
Second, in compilation mode, if <CODE>gnatchop</CODE>
is given a file that starts with
configuration pragmas, and contains one or more units, then these
configuration pragmas are prepended to each of the chopped files. This
behavior provides the required behavior described in the RM for the
actions to be taken on compiling such a file, namely that the pragmas
apply to all units in the compilation, but not to subsequently compiled
units.

</P>
<P>
Finally, if configuration pragmas appear between units, they are appended
to the previous unit. This results in the previous unit being illegal,
since the compiler does not accept configuration pragmas that follow
a unit. This provides the required RM behavior that forbids configuration
pragmas other than those preceding the first compilation unit of a
compilation.

</P>
<P>
For most purposes, <CODE>gnatchop</CODE> will be used in default mode. The
compilation mode described above is used only if you need exactly
accurate behavior with respect to compilations, and you have files
that contain multiple units and configuration pragmas. In this
circumstance the use of <CODE>gnatchop</CODE> with the compilation mode
switch provides the required behavior, and is for example the mode
in which GNAT processes the ACVC tests.

</P>


<H2><A NAME="SEC78" HREF="gnat_ug_toc.html#TOC78">Command Line for <CODE>gnatchop</CODE></A></H2>

<P>
The <CODE>gnatchop</CODE> command has the form:

</P>

<PRE>
   $ gnatchop switches <VAR>file name</VAR> [<VAR>file name</VAR> <VAR>file name</VAR> ...] [<VAR>directory</VAR>]
</PRE>

<P>
The only required argument is the file name of the file to be chopped.
There are no restrictions on the form of this file name. The file itself
contains one or more Ada units, in normal GNAT format, concatenated
together. As shown, more than one file may be presented to be chopped.

</P>
<P>
When run in default mode, <CODE>gnatchop</CODE> generates one output file in
the current directory for each unit in each of the files.

</P>
<P>
<VAR>directory</VAR>, if specified, gives the name of the directory to which
the output files will be written. If it is not specified, all files are
written to the current directory.

</P>
<P>
For example, given a
file called <TT>`hellofiles'</TT> containing

</P>

<PRE>
   <B>procedure</B> hello;

   <B>with</B> Text_IO; <B>use</B> Text_IO;
   <B>procedure</B> hello <B>is</B>
   <B>begin</B>
      Put_Line ("Hello");
   <B>end</B> hello;
</PRE>

<P>
the command

</P>

<PRE>
   $ gnatchop hellofiles
</PRE>

<P>
generates two files in the current directory, one called
<TT>`hello.ads'</TT> containing the single line that is the procedure spec,
and the other called <TT>`hello.adb'</TT> containing the remaining text. The
original file is not affected. The generated files can be compiled in
the normal manner.

</P>


<H2><A NAME="SEC79" HREF="gnat_ug_toc.html#TOC79">Switches for <CODE>gnatchop</CODE></A></H2>

<P>
<CODE>gnatchop</CODE> recognizes the following switches:

</P>
<DL COMPACT>

<DT><CODE>-c</CODE>
<DD>
<A NAME="IDX254"></A>
Causes <CODE>gnatchop</CODE> to operate in compilation mode, in which
configuration pragmas are handled according to strict RM rules. See
previous section for a full description of this mode.

<DT><CODE>-gnatxxx</CODE>
<DD>
This passes the given <CODE>-gnatxxx</CODE> switch to <CODE>gnat</CODE> which is
used to parse the given file. Not all <CODE>xxx</CODE> options make sense,
but for example, the use of <CODE>-gnati2</CODE> allows <CODE>gnatchop</CODE> to
process a source file that uses Latin-2 coding for identifiers.

<DT><CODE>-h</CODE>
<DD>
Causes <CODE>gnatchop</CODE> to generate a brief help summary to the standard
output file showing usage information.

<DT><CODE>-k<VAR>mm</VAR></CODE>
<DD>
<A NAME="IDX255"></A>
Limit generated file names to the specified number <CODE>mm</CODE>
of characters.
This is useful if the
resulting set of files is required to be interoperable with systems
which limit the length of file names.
No space is allowed between the <CODE>-k</CODE> and the numeric value. The numeric
value may be omitted in which case a default of <CODE>-k8</CODE>,
suitable for use
with DOS-like file systems, is used. If no <CODE>-k</CODE> switch
is present then
there is no limit on the length of file names.

<DT><CODE>-q</CODE>
<DD>
<A NAME="IDX256"></A>
Causes output of informational messages indicating the set of generated
files to be suppressed. Warnings and error messages are unaffected.

<DT><CODE>-r</CODE>
<DD>
<A NAME="IDX257"></A>
<A NAME="IDX258"></A>
Generate <CODE>Source_Reference</CODE> pragmas. Use this switch if the output
files are regarded as temporary and development is to be done in terms
of the original unchopped file. This switch causes
<CODE>Source_Reference</CODE> pragmas to be inserted into each of the
generated files to refers back to the original file name and line number.
The result is that all error messages refer back to the original
unchopped file.
In addition, the debugging information placed into the object file (when
the <CODE>-g</CODE> switch of <CODE>gcc</CODE> or <CODE>gnatmake</CODE> is specified) also
refers back to this original file so that tools like profilers and
debuggers will give information in terms of the original unchopped file.

If the original file to be chopped itself contains
a <CODE>Source_Reference</CODE>
pragma referencing a third file, then gnatchop respects
this pragma, and the generated <CODE>Source_Reference</CODE> pragmas
in the chopped file refer to the original file, with appropriate
line numbers. This is particularly useful when <CODE>gnatchop</CODE>
is used in conjunction with <CODE>gnatprep</CODE> to compile files that
contain preprocessing statements and multiple units.

<DT><CODE>-v</CODE>
<DD>
<A NAME="IDX259"></A>
Causes <CODE>gnatchop</CODE> to operate in verbose mode. The version
number and copyright notice are output, as well as exact copies of
the gnat1 commands spawned to obtain the chop control information.

<DT><CODE>-w</CODE>
<DD>
<A NAME="IDX260"></A>
Overwrite existing file names. Normally <CODE>gnatchop</CODE> regards it as a
fatal error if there is already a file with the same name as a
file it would otherwise output, in other words if the files to be
chopped contain duplicated units. This switch bypasses this
check, and causes all but the last instance of such duplicated
units to be skipped.
</DL>



<H2><A NAME="SEC80" HREF="gnat_ug_toc.html#TOC80">Examples of <CODE>gnatchop</CODE> Usage</A></H2>

<DL COMPACT>

<DT><CODE>gnatchop -w hello_s.ada ichbiah/files</CODE>
<DD>
Chops the source file <TT>`hello_s.ada'</TT>. The output files will be
placed in the directory <TT>`ichbiah/files'</TT>,
overwriting any
files with matching names in that directory (no files in the current
directory are modified).

<DT><CODE>gnatchop archive</CODE>
<DD>
Chops the source file <TT>`archive'</TT>
into the current directory.  One
useful application of <CODE>gnatchop</CODE> is in sending sets of sources
around, for example in email messages. The required sources are simply
concatenated (for example, using a UNIX <CODE>cat</CODE>
command), and then
<CODE>gnatchop</CODE> is used at the other end to reconstitute the original
file names.

<DT><CODE>gnatchop file1 file2 file3 direc</CODE>
<DD>
Chops all units in files <TT>`file1'</TT>, <TT>`file2'</TT>, <TT>`file3'</TT>, placing
the resulting files in the directory <TT>`direc'</TT>. Note that if any units
occur more than once anywhere within this set of files, an error message
is generated, and no files are written. To override this check, use the
<CODE>-w</CODE> switch,
in which case the last occurrence in the last file will
be the one that is output, and earlier duplicate occurrences for a given
unit will be skipped.
</DL>



<H1><A NAME="SEC81" HREF="gnat_ug_toc.html#TOC81">Configuration Pragmas</A></H1>
<P>
<A NAME="IDX261"></A>
<A NAME="IDX262"></A>

</P>
<P>
In Ada 95, configuration pragmas include those pragmas described as
such in the Ada 95 Reference Manual, as well as
implementation-dependent pragmas that are configuration pragmas. See the
individual descriptions of pragmas in the GNAT Reference Manual for
details on these additional GNAT-specific configuration pragmas. Most
notably, the pragma <CODE>Source_File_Name</CODE>, which allows
specifying non-default names for source files, is a configuration
pragma.

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC82">Handling of Configuration Pragmas</A>
<LI><A HREF="gnat_ug.html#SEC83">The Configuration Pragmas file</A>
</UL>



<H2><A NAME="SEC82" HREF="gnat_ug_toc.html#TOC82">Handling of Configuration Pragmas</A></H2>

<P>
Configuration pragmas may either appear at the start of a compilation
unit, in which case they apply only to that unit, or they may apply to
all compilations performed in a given compilation environment.

</P>
<P>
GNAT also provides the <CODE>gnatchop</CODE> utility to provide an automatic
way to handle configuration pragmas following the semantics for
compilations (that is, files with multiple units), described in the RM.
See section see section <A HREF="gnat_ug.html#SEC77">Operating gnatchop in Compilation Mode</A> for details.
However, for most purposes, it will be more convenient to edit the
<TT>`gnat.adc'</TT> file that contains configuration pragmas directly,
as described in the following section.

</P>


<H2><A NAME="SEC83" HREF="gnat_ug_toc.html#TOC83">The Configuration Pragmas file</A></H2>
<P>
<A NAME="IDX263"></A>

</P>
<P>
In GNAT a compilation environment is defined by the current
directory at the time that a compile command is given. This current
directory is searched for a file whose name is <TT>`gnat.adc'</TT>. If
this file is present, it is expected to contain one or more
configuration pragmas that will be applied to the current compilation.

</P>
<P>
Configuration pragmas may be entered into the <TT>`gnat.adc'</TT> file
either by running <CODE>gnatchop</CODE> on a source file that consists only of
configuration pragmas, or more conveniently  by
direct editing of the <TT>`gnat.adc'</TT> file, which is a standard format
source file.

</P>



<H1><A NAME="SEC84" HREF="gnat_ug_toc.html#TOC84">Elaboration Order Handling in GNAT</A></H1>
<P>
<A NAME="IDX264"></A>
<A NAME="IDX265"></A>

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC85">Elaboration Code in Ada 95</A>
<LI><A HREF="gnat_ug.html#SEC86">Checking the Elaboration Order in Ada 95</A>
<LI><A HREF="gnat_ug.html#SEC87">Controlling the Elaboration Order in Ada 95</A>
<LI><A HREF="gnat_ug.html#SEC88">Controlling Elaboration in GNAT - Internal Calls</A>
<LI><A HREF="gnat_ug.html#SEC89">Controlling Elaboration in GNAT - External Calls</A>
<LI><A HREF="gnat_ug.html#SEC90">Default Behavior in GNAT - Ensuring Safety</A>
<LI><A HREF="gnat_ug.html#SEC91">What to do if the Default Elaboration Behavior Fails</A>
<LI><A HREF="gnat_ug.html#SEC92">Elaboration for Access-to-Subprogram Values</A>
<LI><A HREF="gnat_ug.html#SEC93">Summary of Procedures for Elaboration Control</A>
</UL>

<P>
This chapter describes the handling of elaboration code in Ada 95 and
in GNAT, and discusses how the order of elaboration of program units can
be controlled in GNAT, either automatically or with explicit programming
features.

</P>


<H2><A NAME="SEC85" HREF="gnat_ug_toc.html#TOC85">Elaboration Code in Ada 95</A></H2>

<P>
Ada 95 provides rather general mechanisms for executing code at elaboration
time, that is to say before the main program starts executing. Such code arises
in three contexts:

</P>
<DL COMPACT>

<DT>Initializers for variables.
<DD>
Variables declared at the library level, in package specs or bodies, can
require initialization that is performed at elaboration time, as in:

<PRE>
   Sqrt_Half : Float := Sqrt (0.5);
</PRE>

<DT>Package initialization code
<DD>
Code in a <CODE>BEGIN-END</CODE> section at the outer level of a package body is
executed as part of the package body elaboration code.

<DT>Library level task allocators
<DD>
Tasks that are declared using task allocators at the library level
start executing immediately and hence can execute at elaboration time.
</DL>

<P>
Subprogram calls are possible in any of these contexts, which means that
any arbitrary part of the program may be executed as part of the elaboration
code. It is even possible to write a program which does all its work at
elaboration time, with a null main program, although stylistically this
would usually be considered an inappropriate way to structure
a program.

</P>
<P>
An important concern arises in the context of elaboration code:
we have to be sure that it is executed in an appropriate order. What we
have is numerous sections of elaboration code, potentially one section
for each unit in the program. It is important that these execute
in the correct order. Correctness here means that, taking the above
example of the declaration of <CODE>Sqrt_Half</CODE>,
that if some other piece of
elaboration code references <CODE>Sqrt_Half</CODE>,
then it must run after the
section of elaboration code that contains the declaration of
<CODE>Sqrt_Half</CODE>.

</P>
<P>
There would never be any order of elaboration problem if we made a rule
that whenever you <CODE>with</CODE> a unit, you must elaborate both the spec and body
of that unit before elaborating the unit doing the <CODE>with</CODE>'ing:

</P>

<PRE>
   <B>with</B> Unit_1;
   <B>package</B> Unit_2 <B>is</B> ...
</PRE>

<P>
would require that both the body and spec of <CODE>Unit_1</CODE> be elaborated
before the spec of <CODE>Unit_2</CODE>. However, a rule like that would be far too
restrictive. In particular, it would make it impossible to have routines
in separate packages that were mutually recursive.

</P>
<P>
You might think that a clever enough compiler could look at the actual
elaboration code and determine an appropriate correct order of elaboration,
but in the general case, this is not possible. Consider the following
example.

</P>
<P>
In the body of <CODE>Unit_1</CODE>, we have a procedure <CODE>Func_1</CODE>
that references
the variable <CODE>Sqrt_1</CODE>, which is declared in the elaboration code
of the body of <CODE>Unit_1</CODE>:

</P>

<PRE>
   Sqrt_1 : Float := Sqrt (0.1);
</PRE>

<P>
The elaboration code of the body of <CODE>Unit_1</CODE> also contains:

</P>

<PRE>
   <B>if</B> expression_1 = 1 <B>then</B>
      Q := Unit_2.Func_2;
   <B>end if</B>;
</PRE>

<P>
<CODE>Unit_2</CODE> is exactly parallel,
it has a procedure <CODE>Func_2</CODE> that references
the variable <CODE>Sqrt_2</CODE>, which is declared in the elaboration code of
the body <CODE>Unit_2</CODE>:

</P>

<PRE>
   Sqrt_2 : Float := Sqrt (0.1);
</PRE>

<P>
The elaboration code of the body of <CODE>Unit_2</CODE> also contains:

</P>

<PRE>
   <B>if</B> expression_2 = 2 <B>then</B>
      Q := Unit_1.Func_1;
   <B>end if</B>;
</PRE>

<P>
Now the question is, which of the following orders of elaboration is
acceptable:

</P>

<PRE>
   Spec of Unit_1
   Spec of Unit_2
   Body of Unit_1
   Body of Unit_2
</PRE>

<P>
or

</P>

<PRE>
   Spec of Unit_2
   Spec of Unit_1
   Body of Unit_2
   Body of Unit_1
</PRE>

<P>
If you carefully analyze the flow here, you will see that you cannot tell
at compile time the answer to this question.
If <CODE>expression_1</CODE> is not equal to 1,
and <CODE>expression_2</CODE> is not equal to 2,
then either order is acceptable, because neither of the function calls is
executed. If both tests evaluate to true, then neither order is acceptable
and in fact there is no correct order.

</P>
<P>
If one of the two expressions is true, and the other is false, then one
of the above orders is correct, and the other is incorrect. For example,
if <CODE>expression_1</CODE> = 1 and <CODE>expression_2</CODE> /= 2,
then the call to <CODE>Func_2</CODE>
will occur, but not the call to <CODE>Func_1.</CODE>
This means that it is essential
to elaborate the body of <CODE>Unit_1</CODE> before
the body of <CODE>Unit_2</CODE>, so the first
order of elaboration is correct and the second is wrong.

</P>
<P>
By making <CODE>expression_1</CODE> and <CODE>expression_2</CODE>
depend on input data, or perhaps
the time of day, we can make it impossible for the compiler or binder
to figure out which of these expressions will be true, and hence it
is impossible to guarantee a safe order of elaboration at run time.

</P>


<H2><A NAME="SEC86" HREF="gnat_ug_toc.html#TOC86">Checking the Elaboration Order in Ada 95</A></H2>

<P>
In some languages that involve the same kind of elaboration problems,
e.g. Java and C++, the programmer is expected to worry about these
ordering problems himself, and it is common to
write a program in which an incorrect elaboration order  gives
surprising results, because it references variables before they
are initialized.
Ada 95 is designed to be a safe language, and a programmer-beware approach is
clearly not sufficient. Consequently, the language provides three lines
of defense:

</P>
<DL COMPACT>

<DT>Standard rules
<DD>
Some standard rules restrict the possible choice of elaboration
order. In particular, if you <CODE>with</CODE> a unit, then its spec is always
elaborated before the unit doing the <CODE>with</CODE>. Similarly, a parent
spec is always elaborated before the child spec, and finally
a spec is always elaborated before its corresponding body.

<DT>Dynamic elaboration checks
<DD>
<A NAME="IDX266"></A>
Dynamic checks are made at run time, so that if some entity is accessed
before it is elaborated (typically  by means of a subprogram call)
then the exception (<CODE>Program_Error</CODE>) is raised.

<DT>Elaboration control
<DD>
Facilities are provided for the programmer to specify the desired order
of elaboration.
</DL>

<P>
Let's look at these facilities in more detail. First, the rules for
dynamic checking. One possible rule would be simply to say that the
exception is raised if you access a variable which has not yet been
elaborated. The trouble with this approach is that it could require
expensive checks on every variable reference. Instead Ada 95 has two
rules which are a little more restrictive, but easier to check, and
easier to state:

</P>
<DL COMPACT>

<DT>Restrictions on calls
<DD>
A subprogram can only be called at elaboration time if its body
has been elaborated. The rules for elaboration given above guarantee
that the spec of the subprogram has been elaborated before the
call, but not the body. If this rule is violated, then the
exception <CODE>Program_Error</CODE> is raised.

<DT>Restrictions on instantiations
<DD>
A generic unit can only be instantiated if the body of the generic
unit has been elaborated. Again, the rules for elaboration given above
guarantee that the spec of the generic unit has been elaborated
before the instantiation, but not the body. if this rule is
violated, then the exception <CODE>Program_Error</CODE> is raised.
</DL>

<P>
The idea is that if the body has been elaborated, then any variables
it references must have been elaborated; by checking for the body being
elaborated we guarantee that none of its references causes any
trouble. As we noted above, this is a little too restrictive, because a
subprogram that has no non-local references in its body may in fact be safe
to call. However, it really would be unsafe to rely on this, because
it would mean that the caller was aware of details of the implementation
in the body. This goes against the basic tenets of Ada.

</P>
<P>
A plausible implementation can be described as follows.
A Boolean variable is associated with each subprogram
and each generic unit. This variable is initialized to False, and is set to
True at the point body is elaborated. Every call or instantiation checks the
variable, and raises <CODE>Program_Error</CODE> if the variable is False.

</P>


<H2><A NAME="SEC87" HREF="gnat_ug_toc.html#TOC87">Controlling the Elaboration Order in Ada 95</A></H2>

<P>
In the previous section we discussed the rules in Ada 95 which ensure
that <CODE>Program_Error</CODE> is raised if an incorrect elaboration order is
chosen. This prevents erroneous executions, but we need mechanisms to
specify a correct execution and avoid the exception altogether.
To achieve this, Ada 95 provides a number of features for controlling
the order of elaboration. We discuss these features in this section.

</P>
<P>
First, there are several ways of indicating to the compiler that a given
unit has no elaboration problems:

</P>
<DL COMPACT>

<DT>packages that do not require a body
<DD>
In Ada 95, a library package that does not require a body does not permit
a body. This means that if we have a such a package, as in:


<PRE>
   <B>package</B> Definitions <B>is</B>
      <B>generic</B>
         <B>type</B> m <B>is new</B> integer;
      <B>package</B> Subp <B>is</B>
         <B>type</B> a <B>is array</B> (1 .. 10) <B>of</B> m;
         <B>type</B> b <B>is array</B> (1 .. 20) <B>of</B> m;
      <B>end</B> Subp;
   <B>end</B> Definitions;
</PRE>

A package that <CODE>with</CODE>'s <CODE>Definitions</CODE> may safely instantiate
<CODE>Definitions.Subp</CODE> because the compiler can determine that there
definitely is no package body to worry about in this case

<DT>pragma Pure
<DD>
<A NAME="IDX267"></A>
<A NAME="IDX268"></A>
Places sufficient restrictions on a unit to guarantee that
no call to any subprogram in the unit can result in an
elaboration problem. This means that the compiler does not need
to worry about the point of elaboration of such units, and in
particular, does not need to check any calls to any subprograms
in this unit.

<DT>pragma Preelaborate
<DD>
<A NAME="IDX269"></A>
<A NAME="IDX270"></A>
This pragma places slightly less stringent restrictions on a unit than
does pragma Pure,
but these restrictions are still sufficient to ensure that there
are no elaboration problems with any calls to the unit.

<DT>pragma Elaborate_Body
<DD>
<A NAME="IDX271"></A>
<A NAME="IDX272"></A>
This pragma requires that the body of a unit be elaborated immediately
after its spec. Suppose a unit <CODE>A</CODE> has such a pragma,
and unit <CODE>B</CODE> does
a <CODE>with</CODE> of unit <CODE>A</CODE>. Recall that the standard rules require
the spec of unit <CODE>A</CODE>
to be elaborated before the <CODE>with</CODE>'ing unit; given the pragma in
<CODE>A</CODE>, we also know that the body of <CODE>A</CODE>
will be elaborated before <CODE>B</CODE>, so
that calls to <CODE>A</CODE> are safe and do not need a check.
</DL>

<P>
Note that,
unlike pragma <CODE>Pure</CODE> and pragma <CODE>Preelaborate</CODE>,
the use of
<CODE>Elaborate_Body</CODE> does not guarantee that the program is
free of elaboration problems, because it may not be possible
to satisfy the requested elaboration order.
Let's go back to the example with <CODE>Unit_1</CODE> and <CODE>Unit_2</CODE>.
If a programmer
marks <CODE>Unit_1</CODE> as <CODE>Elaborate_Body</CODE>,
and not <CODE>Unit_2,</CODE> then the order of
elaboration will be:

</P>

<PRE>
   Spec of Unit_2
   Spec of Unit_1
   Body of Unit_1
   Body of Unit_2
</PRE>

<P>
Now that means that the call to <CODE>Func_1</CODE> in <CODE>Unit_2</CODE>
need not be checked,
it must be safe. But the call to <CODE>Func_2</CODE> in
<CODE>Unit_1</CODE> may still fail if
<CODE>Expression_1</CODE> is equal to 1,
and the programmer must still take
responsibility for this not being the case.

</P>
<P>
If all units carry a pragma <CODE>Elaborate_Body</CODE>, then all problems are
eliminated, except for calls entirely within a body, which are
in any case fully under programmer control. However, using the pragma
everywhere is not always possible.
In particular, for our <CODE>Unit_1</CODE>/<CODE>Unit_2</CODE> example, if
we marked both of them as having pragma <CODE>Elaborate_Body</CODE>, then
clearly there would be no possible elaboration order.

</P>
<P>
The above pragmas allow a server to guarantee safe use by clients, and
clearly this is the preferable approach. Consequently a good rule in
Ada 95 is to mark units as <CODE>Pure</CODE> or <CODE>Preelaborate</CODE> if possible,
and if this is not possible,
mark them as <CODE>Elaborate_Body</CODE> if possible.
As we have seen, there are situation where neither of these
three pragmas can be used.
So we also provide methods for clients to control the
order of elaboration of the servers on which they depend:

</P>
<DL COMPACT>

<DT>pragma Elaborate (unit)
<DD>
<A NAME="IDX273"></A>
<A NAME="IDX274"></A>
This pragma is placed in the context clause, after a <CODE>with</CODE> statement,
and it requires that the body of the named unit be elaborated before
the unit in which the pragma occurs. The idea is to use this pragma
if the current unit calls at elaboration time, directly or indirectly,
some subprogram in the named unit.

<DT>pragma Elaborate_All (unit)
<DD>
<A NAME="IDX275"></A>
<A NAME="IDX276"></A>
This is a stronger version of the Elaborate pragma. Consider the
following example:


<PRE>
   Unit A <CODE>with</CODE>'s unit B and calls B.Func in elaboration code
   Unit B <CODE>with</CODE>'s unit C, and B.Func calls C.Func
</PRE>

Now if we put a pragma <CODE>Elaborate (B)</CODE>
in unit <CODE>A</CODE>, this ensures that the
body of <CODE>B</CODE> is elaborated before the call, but not the
body of <CODE>C</CODE>, so
the call to <CODE>C.Func</CODE> could still cause <CODE>Program_Error</CODE> to
be raised.

The effect of a pragma <CODE>Elaborate_All</CODE> is stronger, it requires
not only that the body of the named unit be elaborated before the
unit doing the <CODE>with</CODE>, but also the bodies of all units that the
named unit uses, following <CODE>with</CODE> links transitively. For example,
if we put a pragma <CODE>Elaborate_All (B)</CODE> in unit <CODE>A</CODE>,
then it requires
not only that the body of <CODE>B</CODE> be elaborated before <CODE>A</CODE>,
but also the
body of <CODE>C</CODE>, because <CODE>B</CODE> <CODE>with</CODE>'s <CODE>C</CODE>.
</DL>

<P>
We are now in a position to give a usage rule in Ada 95 for avoiding
elaboration problems, at least if dynamic dispatching and access to
subprogram values are not used. We will handle these cases separately
later.

</P>
<P>
The rule is simple. If a unit has elaboration code that can directly or
indirectly make a call to a subprogram in a <CODE>with</CODE>'ed unit, or instantiate
a generic unit in a <CODE>with</CODE>'ed unit,
then if the <CODE>with</CODE>'ed unit does not have
pragma Pure, Preelaborate, or Elaborate_Body, then the client should have
an Elaborate_All for the <CODE>with</CODE>'ed unit. By following this rule a client is
assured that calls can be made without risk of an exception.
If this rule is not followed, then a program may be in one of four
states:

</P>
<DL COMPACT>

<DT>No order exists
<DD>
No order of elaboration exists which follows the rules, taking into
account any Elaborate, Elaborate_All, or Elaborate_Body pragmas. In
this case, an Ada 95 compiler must diagnose the situation at bind
time, and refuse to build an executable program.

<DT>One or more orders exist, all incorrect
<DD>
One or more acceptable elaboration orders exists, and all of them
generate an elaboration order problem. In this case, the binder
can build an executable program, but Program_Error will be raised
when the program is run.

<DT>Several orders exist, some right, some incorrect
<DD>
One or more acceptable elaboration orders exists, and some of them
work, and some do not. The programmer has not controlled
the order of elaboration, so the binder may or may not pick one of
the correct orders, and the program may or may not raise an
exception when it is run. This is the worst case, because it means
that the program may fail when moved to another compiler, or even
another version of the same compiler.

<DT>One or more orders exists, all correct
<DD>
One ore more acceptable elaboration orders exist, and all of them
work. In this case the program runs successfully. This state of
affairs can be guaranteed by following the rule we gave above, but
may be true even if the rule is not followed.
</DL>

<P>
Note that one additional advantage of following our Elaborate_All rule
is that the program continues to stay in the ideal (all orders OK) state
even if maintenance
changes some bodies of some subprograms. Conversely, if a program that does
not follow this rule happens to be safe at some point, this state of affairs
may deteriorate silently as a result of maintenance changes.

</P>


<H2><A NAME="SEC88" HREF="gnat_ug_toc.html#TOC88">Controlling Elaboration in GNAT - Internal Calls</A></H2>

<P>
In the case of internal calls, i.e. calls within a single package, the
programmer has full control over the order of elaboration, and it is up
to the programmer to elaborate declarations in an appropriate order. For
example writing:

</P>

<PRE>
   <B>function</B> One <B>return</B> Float;

   Q : Float := One;

   <B>function</B> One <B>return</B> Float <B>is</B>
   <B>begin</B>
        return 1.0;
   <B>end</B> One;
</PRE>

<P>
will obviously raise Program_Error at run time, because function One will be
called before its body is elaborated.  In this case GNAT will generate
a warning that the call will raise Program_Error:

</P>

<PRE>
    1. procedure y is
    2.    function One return Float;
    3.
    4.    Q : Float := One;
                       |
       &#62;&#62;&#62; warning: cannot call "One" before body is elaborated
       &#62;&#62;&#62; warning: Program_Error will be raised at run time

    5.
    6.    function One return Float is
    7.    begin
    8.         return 1.0;
    9.    end One;
   10.
   11. begin
   12.    null;
   13. end;
</PRE>

<P>
Note that in this particular case, it is likely that the call is safe, because
the function <CODE>One</CODE> does not access any global variables.
Nevertheless in Ada 95, we do not want the validity of the check to depend on
the contents of the body (think about the separate compilation case), so this
is still wrong, as we discussed in the previous sections.

</P>
<P>
The error is easily corrected by rearranging the declarations so that the
body of One appears before the declaration containing the call
(note that in Ada 95,
declarations can appear in any order, so there is no restriction that
would prevent this reordering, and if we write:

</P>

<PRE>
   <B>function</B> One <B>return</B> Float;

   <B>function</B> One <B>return</B> Float <B>is</B>
   <B>begin</B>
        return 1.0;
   <B>end</B> One;

   Q : Float := One;
</PRE>

<P>
then all is well, no warning is generated, and no
<CODE>Program_Error</CODE> exception
will be raised.
Things are more complicated when a chain of subprograms is executed:

</P>

<PRE>
   <B>function</B> A <B>return</B> Integer;
   <B>function</B> B <B>return</B> Integer;
   <B>function</B> C <B>return</B> Integer;

   <B>function</B> B <B>return</B> Integer <B>is begin return</B> A; <B>end</B>;
   <B>function</B> C <B>return</B> Integer <B>is begin return</B> B; <B>end</B>;

   X : Integer := C;

   <B>function</B> A <B>return</B> Integer <B>is begin return</B> 1; <B>end</B>;
</PRE>

<P>
Now the call to <CODE>C</CODE>
at elaboration time in the declaration of <CODE>X</CODE> is correct, because
the body of <CODE>C</CODE> is already elaborated,
and the call to <CODE>B</CODE> within the body of
<CODE>C</CODE> is correct, but the call
to <CODE>A</CODE> within the body of <CODE>B</CODE> is incorrect, because the body
of <CODE>A</CODE> has not been elaborated, so <CODE>Program_Error</CODE>
will be raised on the call to <CODE>A</CODE>.
In this case GNAT will generate a
warning that <CODE>Program_Error</CODE> may be
raised at the point of the call. Let's look at the warning:

</P>

<PRE>
    1. procedure x is
    2.    function A return Integer;
    3.    function B return Integer;
    4.    function C return Integer;
    5.
    6.    function B return Integer is begin return A; end;
                                                    |
       &#62;&#62;&#62; warning: call to "A" before body is elaborated may
                    raise Program_Error
       &#62;&#62;&#62; warning: "B" called at line 7
       &#62;&#62;&#62; warning: "C" called at line 9

    7.    function C return Integer is begin return B; end;
    8.
    9.    X : Integer := C;
   10.
   11.    function A return Integer is begin return 1; end;
   12.
   13. begin
   14.    null;
   15. end;
</PRE>

<P>
Note that the message here says "may raise", instead of the direct case,
where the message says "will be raised". That's because whether
<CODE>A</CODE> is
actually called depends in general on run-time flow of control.
For example, if the body of <CODE>B</CODE> said

</P>

<PRE>
   <B>function</B> B <B>return</B> Integer <B>is</B>
   <B>begin</B>
      <B>if</B> some-condition-depending-on-input-data <B>then</B>
         <B>return</B> A;
      <B>else</B>
         <B>return</B> 1;
      <B>end if</B>;
   <B>end</B> B;
</PRE>

<P>
then we could not know until run time whether the incorrect call to A would
actually occur, so <CODE>Program_Error</CODE> might
or might not be raised. It is possible for a compiler to
do a better job of analyzing bodies, to
determine whether or not <CODE>Program_Error</CODE>
might be raised, but it certainly
couldn't do a perfect job (that would require solving the halting problem
and is provably impossible), and because this is a warning anyway, it does
not seem worth the effort to do the analysis. Cases in which it
would be relevant are rare.

</P>
<P>
In practice, warnings of either of the forms given
above will usually correspond to
real errors, and should be examined carefully and eliminated.
In the rare case where a warning is bogus, it can be suppressed by any of
the following methods:

</P>

<UL>
<LI>

Compile with the <CODE>-gnatws</CODE> switch set

<LI>

Suppress <CODE>Elaboration_Checks</CODE> for the called subprogram

<LI>

Use pragma <CODE>Warnings_Off</CODE> to turn warnings off for the call
</UL>

<P>
For the internal elaboration check case,
GNAT by default generates the
necessary run-time checks to ensure
that <CODE>Program_Error</CODE> is raised if any
call fails an elaboration check. Of course this can only happen if a
warning has been issued as described above. The use of pragma
<CODE>Suppress (Elaboration_Checks)</CODE> may (but is not guaranteed) to suppress
some of these checks, meaning that it may be possible (but is not
guaranteed) for a program to be able to call a subprogram whose body
is not yet elaborated, without raising a <CODE>Program_Error</CODE> exception.

</P>


<H2><A NAME="SEC89" HREF="gnat_ug_toc.html#TOC89">Controlling Elaboration in GNAT - External Calls</A></H2>

<P>
The previous section discussed the case in which the execution of a
particular thread of elaboration code occurred entirely within a
single unit. This is the easy case to handle, because a programmer
has direct and total control over the order of elaboration, and
furthermore, checks need only be generated in cases which are rare
and which the compiler can easily detect.
The situation is more complex when separate compilation is taken into account.
Consider the following:

</P>

<PRE>
   <B>package</B> Math <B>is</B>
      <B>function</B> Sqrt (Arg : Float) <B>return</B> Float;
   <B>end</B> Math;

   <B>package body</B> Math <B>is</B>
      <B>function</B> Sqrt (Arg : Float) <B>return</B> Float <B>is</B>
      <B>begin</B>
         ...
      <B>end</B> Sqrt;
   <B>end</B> Math;
   <B>with</B> Math;
   <B>package</B> Stuff <B>is</B>
      X : Float := Math.Sqrt (0.5);
   <B>end</B> Stuff;

   <B>with</B> Stuff;
   <B>procedure</B> Main <B>is</B>
   <B>begin</B>
      ...
   <B>end</B> Main;
</PRE>

<P>
where <CODE>Main</CODE> is the main program. When this program is executed, the
elaboration code must first be executed, and one of the jobs of the
binder is to determine the order in which the units of a program are
to be elaborated. In this case we have four units: the spec and body
of <CODE>Math</CODE>,
the spec of <CODE>Stuff</CODE> and the body of <CODE>Main</CODE>).
In what order should the four separate sections of elaboration code
be executed?

</P>
<P>
There are some restrictions in the order of elaboration that the binder
can choose. In particular, if unit U has a <CODE>with</CODE>
for a package <CODE>X</CODE>, then you
are assured that the spec of <CODE>X</CODE>
is elaborated before U , but you are
not assured that the body of <CODE>X</CODE>
is elaborated before U.
This means that in the above case, the binder is allowed to choose the
order:

</P>

<PRE>
   spec of Math
   spec of Stuff
   body of Math
   body of Main
</PRE>

<P>
but that's not good, because now the call to <CODE>Math.Sqrt</CODE>
that happens during
the elaboration of the <CODE>Stuff</CODE>
spec happens before the body of <CODE>Math.Sqrt</CODE> is
elaborated, and hence causes <CODE>Program_Error</CODE> exception to be raised.
At first glance, one might say that the binder is misbehaving, because
obviously you want to elaborate the body of something you <CODE>with</CODE>
first, but
that is not a general rule that can be followed in all cases. Consider

</P>

<PRE>
   <B>package</B> X <B>is</B> ...

   <B>package</B> Y <B>is</B> ...

   <B>with</B> X;
   <B>package body</B> Y <B>is</B> ...

   <B>with</B> Y;
   <B>package body</B> X <B>is</B> ...
</PRE>

<P>
This is a common arrangement, and, apart from the order of elaboration
problems that might arise in connection with elaboration code, this works fine.
A rule that says that you must first elaborate the body of anything you
<CODE>with</CODE> cannot work in this case
(the body of <CODE>X</CODE> <CODE>with</CODE>'s <CODE>Y</CODE>,
which means you would have to
elaborate the body of <CODE>Y</CODE> first, but that <CODE>with</CODE>'s <CODE>X</CODE>,
which means
you have to elaborate the body of <CODE>X</CODE> first, but ... and we have a
loop that cannot be broken.

</P>
<P>
It is true that the binder can in many cases guess an order of elaboration
that is unlikely to cause a <CODE>Program_Error</CODE>
exception to be raised, and it tries to do so (in the
above example of <CODE>Math/Stuff/Spec</CODE>, the GNAT binder will
in fact always
elaborate the body of <CODE>Math</CODE> right after its spec, so all will be well).

</P>
<P>
However, a program that blindly relies on the binder to be helpful can
get into trouble, as we discussed in the previous sections, so
GNAT
provides a number of facilities for assisting the programmer in
developing programs that are robust with respect to elaboration order.

</P>


<H2><A NAME="SEC90" HREF="gnat_ug_toc.html#TOC90">Default Behavior in GNAT - Ensuring Safety</A></H2>

<P>
The default behavior in GNAT ensures elaboration safety. In its
default mode GNAT implements the
rule we previously described as the right approach. Let's restate it:

</P>
<P>
If a unit has elaboration code that can directly or indirectly make a
call to a subprogram in a <CODE>with</CODE>'ed unit, or instantiate a generic unit
in a <CODE>with</CODE>'ed unit, then if the <CODE>with</CODE>'ed unit
does not have pragma <CODE>Pure</CODE>,
<CODE>Preelaborate</CODE>, or <CODE>Elaborate_Body</CODE>,
then the client should have an
<CODE>Elaborate_All</CODE> for the <CODE>with</CODE>'ed unit. By following this rule a client
is assured that calls and instantiations can be made without risk of an exception.

</P>
<P>
In this mode GNAT traces all calls that are potentially made from
elaboration code, and put in any missing implicit <CODE>Elaborate_All</CODE>
pragmas.
The advantage of this approach is that no elaboration problems
are possible if the binder can find an elaboration order that is
consistent with these implicit <CODE>Elaborate_All</CODE> pragmas. The
disadvantage of this approach is that no such order may exist.

</P>
<P>
If the binder does not generate any diagnostics, then it means that it
has found an elaboration order that is guaranteed to be safe. However,
the binder may still be relying on implicitly generated
<CODE>Elaborate_All</CODE> pragmas so portability to other compilers than
GNAT is not guaranteed.

</P>
<P>
If it is important to guarantee portability, then the compilations should
use the
<CODE>-gnatwl</CODE>
(warn on elaboration problems) switch. This will cause warning messages
to be generated indicating the missing <CODE>Elaborate_All</CODE> pragmas.
Consider the following source program:

</P>

<PRE>
   <B>with</B> k;
   <B>package</B> j <B>is</B>
     m : integer := k.r;
   <B>end</B>;
</PRE>

<P>
where it is clear that there
should be a pragma <CODE>Elaborate_All</CODE>
for unit <CODE>k</CODE>. An implicit pragma will be generated, and it is
likely that the binder will be able to honor it. However,
it is safer to include the pragma explicitly in the source. If this
unit is compiled with the
<CODE>-gnatwl</CODE>
switch, then the compiler outputs a warning:

</P>

<PRE>
   1. with k;
   2. package j is
   3.   m : integer := k.r;
                        |
      &#62;&#62;&#62; warning: call to "r" may raise Program_Error
      &#62;&#62;&#62; warning: missing pragma Elaborate_All for "k"

   4. end;
</PRE>

<P>
and these warnings can be used as a guide for supplying manually
the missing pragmas.

</P>


<H2><A NAME="SEC91" HREF="gnat_ug_toc.html#TOC91">What to do if the Default Elaboration Behavior Fails</A></H2>

<P>
If the binder cannot find an acceptable order, it outputs detailed
diagnostics. For example:

</P>

<PRE>
   error: elaboration circularity detected
   info:   "proc (body)" must be elaborated before "pack (body)"
   info:     reason: Elaborate_All probably needed in unit "pack (body)"
   info:     recompile "pack (body)" with -gnatwl
   info:                             for full details
   info:       "proc (body)"
   info:         is needed by its spec:
   info:       "proc (spec)"
   info:         which is withed by:
   info:       "pack (body)"
   info:  "pack (body)" must be elaborated before "proc (body)"
   info:     reason: pragma Elaborate in unit "proc (body)"
</PRE>

<P>
In this case we have a cycle that the binder cannot break. On the one
hand, there is an explicit pragma Elaborate in <CODE>proc</CODE> for
<CODE>pack</CODE>. This means that the body of <CODE>pack</CODE> must be elaborated
before the body of <CODE>proc</CODE>. On the other hand, there is elaboration
code in <CODE>pack</CODE> that calls a subprogram in <CODE>proc</CODE>. This means
that for maximum safety, there should really be a pragma
Elaborate_All in <CODE>pack</CODE> for <CODE>proc</CODE> which would require that
the body of <CODE>proc</CODE> be elaborated before the body of
<CODE>pack</CODE>. Clearly both requirements cannot be satisfied.
Faced with a circularity of this kind, you have three different options.

</P>
<DL COMPACT>

<DT>Fix the program
<DD>
The most desirable option from the point of view of long-term maintenance
is to rearrange the program so that the elaboration problems are avoided.
One useful technique is to place the elaboration code into separate
child packages. Another is to move some of the initialization code to
explicitly called subprograms, where the program controls the order
of initialization explicitly. Although this is the most desirable option,
it may be impractical and involve too much modification, especially in
the case of complex legacy code.

<DT>Perform dynamic checks
<DD>
If the compilations are done using the
<CODE>-gnatE</CODE>
(dynamic elaboration check) switch, then GNAT behaves in
a quite different manner. Dynamic checks are generated for all calls
that could possibly result in raising an exception. With this switch,
the compiler does not generate implicit <CODE>Elaborate_All</CODE> pragmas.
The behavior then is exactly as specified in the Ada 95 Reference Manual.
The binder will generate an executable program that may or may not
raise Program_Error, and then it is the programmer's job to ensure
that it does not raise an exception. Note that it is important to
compile all units with the switch, it cannot be used selectively.

<DT>Suppress checks
<DD>
The drawback of dynamic checks is that they generate a
significant overhead at run time, both in space and time. If you
are absolutely sure that your program cannot raise any elaboration
exceptions, then you can use the
<CODE>-f</CODE>
switch for the
<CODE>gnatbind</CODE>
step, or
<CODE>-bargs -f</CODE>
if you are using
<CODE>gnatmake</CODE>.
This switch tells the binder to ignore any implicit <CODE>Elaborate_All</CODE>
pragmas that were generated by the compiler, and suppresses any
circularity messages that they cause. The resulting executable will work
properly if there are no elaboration problems, but if there are some order of
elaboration problems they will not be detected, and unexpected
results may occur.
</DL>

<P>
It is hard to generalize on which of these three approaches should be
taken. Obviously if it is possible to fix the program so that the default
treatment works, this is preferable, but this may not always be practical.
It is certainly simple enough to use
<CODE>-gnatE</CODE>
or
<CODE>-f</CODE>
but the danger in either case is that, even if the GNAT binder
finds a correct elaboration order, it may not always do so,
and certainly a binder from another Ada compiler might not. A
combination of testing and analysis (for which the warnings generated
with the
<CODE>-gnatwl</CODE>
switch can be useful) must be used to ensure that the program is free
of errors. One switch that is useful in this testing is the
<CODE>-h (horrible elaboration order)</CODE>
switch for
<CODE>gnatbind</CODE>.
Normally the binder tries to find an order that has the best chance of
of avoiding elaboration problems. With this switch, the binder
plays a devil's advocate role, and tries to choose the order that
has the best chance of failing. If your program works even with this
switch, then it has a better chance of being error free, but this is still
not a guarantee.

</P>
<P>
For an example of this approach in action, consider the C-tests (executable
tests) from the ACVC suite. If these are compiled and run with the default
treatment, then all but one of them succeed without generating any error
diagnostics from the binder. However, there is one test that fails, and
this is not surprising, because the whole point of this test is to ensure
that the compiler can handle cases where it is impossible to determine
a correct order statically, and it checks that an exception is indeed
raised at run time.

</P>
<P>
This one test must be compiled and run using the
<CODE>-gnatE</CODE>
switch, and then it passes. Alternatively, the entire suite can
be run using this switch. It is never wrong to run with the dynamic
elaboration switch if your code is correct, and we assume that the
C-tests are indeed correct (it is less efficient, but efficiency is
not a factor in running the ACVC tests.)

</P>


<H2><A NAME="SEC92" HREF="gnat_ug_toc.html#TOC92">Elaboration for Access-to-Subprogram Values</A></H2>
<P>
<A NAME="IDX277"></A>

</P>
<P>
The introduction of access-to-subprogram types in Ada 95 complicates
the handling of elaboration. The trouble is that it becomes
impossible to tell at compile time which procedure
is being called. This means that it is not possible for the binder
to analyze the elaboration requirements in this case.

</P>
<P>
If at the point at which  the access value is created, the body of the subprogram is
known to have been elaborated, then the access value is safe, and its use
does not require a check. This may be achieved by appropriate arrangement
of the order of declarations if the subprogram is in the current unit,
or, if the subprogram is in another unit, by using pragma
<CODE>Pure</CODE>, <CODE>Preelaborate</CODE>, or <CODE>Elaborate_Body</CODE>
on the referenced unit.

</P>
<P>
If the referenced body is not known to have been elaborated at the point
the access value is created, then any use of the access value must do a
dynamic check, and this dynamic check will fail and raise a
<CODE>Program_Error</CODE> exception if the body has not been elaborated yet.
GNAT will generate the necessary checks, and in addition, if the
<CODE>-gnatwl</CODE>
switch is set, will generate warnings that such checks are required.

</P>
<P>
The use of dynamic dispatching for tagged types similarly generates
a requirement for dynamic checks, and premature calls to any primitive
operation of a tagged type before the body of the operation has been elaborated,
will result in the raising of <CODE>Program_Error</CODE>.

</P>


<H2><A NAME="SEC93" HREF="gnat_ug_toc.html#TOC93">Summary of Procedures for Elaboration Control</A></H2>
<P>
<A NAME="IDX278"></A>

</P>
<P>
First, compile your program with the default options, using none of
the special elaboration control switches. If the binder successfully
binds your program, then you can be confident that, apart from issues
raised by the use of access-to-subprogram types and dynamic dispatching,
the program is free of elaboration errors. If it is important that the
program be portable, then use the
<CODE>-gnatwl</CODE>
switch to generate warnings about missing <CODE>Elaborate_All</CODE>
pragmas, and supply the missing pragmas.

</P>
<P>
If the program fails to bind using the default static elaboration
handling, then you can fix the program to eliminate the binder
message, or recompile the entire program with the
<CODE>-gnatE</CODE> switch to generate dynamic elaboration checks,
or, if you are sure there really are no elaboration problems,
use the
<CODE>-f</CODE>
switch for the binder to cause it to ignore implicit <CODE>Elaborate_All</CODE>
pragmas generated by the compiler.

</P>



<H1><A NAME="SEC94" HREF="gnat_ug_toc.html#TOC94">The cross-referencing tools <CODE>gnatxref</CODE> and <CODE>gnatfind</CODE></A></H1>
<P>
<A NAME="IDX279"></A>
<A NAME="IDX280"></A>

</P>
<P>
The compiler generates cross-referencing information (unless
you set the <SAMP>`-gnatx'</SAMP> switch), which are saved in the <TT>`.ali'</TT> files.
This information indicates where in the source each entity is declared and
referenced.

</P>
<P>
Before using any of these two tools, you need to compile successfully your
application, so that GNAT gets a chance to generate the cross-referencing
information.

</P>
<P>
The two tools <CODE>gnatxref</CODE> and <CODE>gnatfind</CODE> take advantage of this
information to provide the user with the capability to easily locate the
declaration and references to an entity. These tools are quite similar,
the difference being that <CODE>gnatfind</CODE> is intended for locating
definitions and/or references to a specified entity or entities, whereas
<CODE>gnatxref</CODE> is oriented to generating a full report of all
cross-references.

</P>
<P>
To use these tools, you must not compile your application using the
<SAMP>`-gnatx'</SAMP> switch on the <TT>`gnatmake'</TT> command line (See Info file `gnat_ug', node `The GNAT Make Program gnatmake'). Otherwise, cross-referencing
information will not be generated.

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC95">Gnatxref switches</A>
<LI><A HREF="gnat_ug.html#SEC96">Gnatfind switches</A>
<LI><A HREF="gnat_ug.html#SEC97">Project files</A>
<LI><A HREF="gnat_ug.html#SEC98">Regular expressions in gnatfind and gnatxref</A>
<LI><A HREF="gnat_ug.html#SEC99">Examples of gnatxref usage</A>
<LI><A HREF="gnat_ug.html#SEC102">Examples of gnatfind usage</A>
</UL>



<H2><A NAME="SEC95" HREF="gnat_ug_toc.html#TOC95">Gnatxref switches</A></H2>

<P>
The command lines for <CODE>gnatxref</CODE> is:

<PRE>
   $ gnatxref [switches] sourcefile1 [sourcefile2 ...]
</PRE>

<P>
where

</P>
<DL COMPACT>

<DT><CODE>sourcefile1, sourcefile2</CODE>
<DD>
identifies the source files for which a report is to be generated. The
'with'ed units will be processed too. You must provide at least one file.

These file names are considered to be regular expressions, so for instance
specifying 'source*.adb' is the same as giving every file in the current
directory whose name starts with 'source' and whose extension is 'adb'.

</DL>

<P>
The switches can be :
<DL COMPACT>

<DT><CODE>-a</CODE>
<DD>
If this switch is present, <CODE>gnatfind</CODE> and <CODE>gnatxref</CODE> will parse
the read-only files found in the library search path. Otherwise, these files
will be ignored. This option can be used to protect Gnat sources or your own
libraries from being parsed, thus making <CODE>gnatfind</CODE> and <CODE>gnatxref</CODE>
much faster, and their output much smaller.

<DT><CODE>-aIDIR</CODE>
<DD>
When looking for source files also look in directory DIR. The order in which
source file search is undertaken is the same as for <TT>`gnatmake'</TT>.

<DT><CODE>-aODIR</CODE>
<DD>
When searching for library and object files, look in directory
DIR. The order in which library files are searched is the same as for
<TT>`gnatmake'</TT>.

<DT><CODE>-f</CODE>
<DD>
If this switch is set, the output file names will be preceded by their
directory (if the file was found in the search path). If this switch is
not set, the directory will not be printed.

<DT><CODE>-g</CODE>
<DD>
If this switch is set, information is output only for library-level
entities, ignoring local entities. The use of this switch may accelerate
<CODE>gnatfind</CODE> and <CODE>gnatxref</CODE>.

<DT><CODE>-IDIR</CODE>
<DD>
Equivalent to <SAMP>`-aODIR -aIDIR'</SAMP>.

<DT><CODE>-pFILE</CODE>
<DD>
Specify a project file to use See section <A HREF="gnat_ug.html#SEC97">Project files</A>.
By default, <CODE>gnatxref</CODE> and <CODE>gnatfind</CODE> will try to locate a
project file in the current directory.

If a project file is either specified or found by the tools, then the content
of the source directory and object directory lines are added as if they
had been specified respectively by <SAMP>`-aI'</SAMP>
and <SAMP>`-aO'</SAMP>.
<DT><CODE>-u</CODE>
<DD>
Output only unused symbols. This may be really useful if you give your
main compilation unit on the command line, as <CODE>gnatxref</CODE> will then
display every unused entity and 'with'ed package.

<DT><CODE>-v</CODE>
<DD>
Instead of producing the default output, <CODE>gnatxref</CODE> will generate a
<TT>`tags'</TT> file that can be used by vi. For examples how to use this
feature, see See section <A HREF="gnat_ug.html#SEC99">Examples of <CODE>gnatxref</CODE> usage</A>. The tags file is output
to the standard output, thus you will have to redirect it to a file.

</DL>

<P>
All these switches may be in any order on the command line, and may even
appear after the file names. They need not be separated by spaces, thus
you can say <SAMP>`gnatxref -ag'</SAMP> instead of
<SAMP>`gnatxref -a -g'</SAMP>.

</P>



<H2><A NAME="SEC96" HREF="gnat_ug_toc.html#TOC96">Gnatfind switches</A></H2>

<P>
The command line for <CODE>gnatfind</CODE> is:

</P>

<PRE>
   $ gnatfind [switches] pattern[:sourcefile[:line[:column]]] [file1 file2 ...]
</PRE>

<P>
where

</P>
<DL COMPACT>

<DT><CODE>pattern</CODE>
<DD>
An entity will be output only if it matches the regular expression found
in <SAMP>`pattern'</SAMP>, see See section <A HREF="gnat_ug.html#SEC98">Regular expressions in gnatfind and gnatxref</A>.

Omitting the pattern is equivalent to specifying <SAMP>`*'</SAMP>, which
will match any entity. Note that if you do not provide a pattern, you
have to provide both a sourcefile and a line.

Entity names are given in Latin-1, with upper-lower case equivalence
for matching purposes. At the current time there is no support for
8-bit codes other than Latin-1, or for wide characters in identifiers.

<DT><CODE>sourcefile</CODE>
<DD>
<CODE>gnatfind</CODE> will look for references, bodies or declarations
of symbols referenced in <TT>`sourcefile'</TT>, at line <SAMP>`line'</SAMP>
and column <SAMP>`column'</SAMP>. See see section <A HREF="gnat_ug.html#SEC102">Examples of <CODE>gnatfind</CODE> usage</A>
for syntax examples.

<DT><CODE>line</CODE>
<DD>
is a decimal integer identifying the line number containing
the reference to the entity (or entities) to be located.

<DT><CODE>column</CODE>
<DD>
is a decimal integer identifying the exact location on the
line of the first character of the identifier for the
entity reference. Columns are numbered from 1.

<DT><CODE>file1 file2 ...</CODE>
<DD>
The search will be restricted to these files. If none are given, then
the search will be done for every library file in the search path.
These file must appear only after the pattern or sourcefile.

These file names are considered to be regular expressions, so for instance
specifying 'source*.adb' is the same as giving every file in the current
directory whose name starts with 'source' and whose extension is 'adb'.

Not that if you specify at least one file in this part, <CODE>gnatfind</CODE> may
sometimes not be able to find the body of the subprograms...

</DL>

<P>
At least one of 'sourcefile' or 'pattern' has to be present on
the command line.

</P>
<P>
The following switches are available:
<DL COMPACT>

<DT><CODE>-a</CODE>
<DD>
If this switch is present, <CODE>gnatfind</CODE> and <CODE>gnatxref</CODE> will parse
the read-only files found in the library search path. Otherwise, these files
will be ignored. This option can be used to protect Gnat sources or your own
libraries from being parsed, thus making <CODE>gnatfind</CODE> and <CODE>gnatxref</CODE>
much faster, and their output much smaller.

<DT><CODE>-aIDIR</CODE>
<DD>
When looking for source files also look in directory DIR. The order in which
source file search is undertaken is the same as for <TT>`gnatmake'</TT>.

<DT><CODE>-aODIR</CODE>
<DD>
When searching for library and object files, look in directory
DIR. The order in which library files are searched is the same as for
<TT>`gnatmake'</TT>.

<DT><CODE>-e</CODE>
<DD>
By default, <CODE>gnatfind</CODE> accept the simple regular expression set for
<SAMP>`pattern'</SAMP>. If this switch is set, then the pattern will be
considered as full Unix-style regular expression.

<DT><CODE>-f</CODE>
<DD>
If this switch is set, the output file names will be preceded by their
directory (if the file was found in the search path). If this switch is
not set, the directory will not be printed.

<DT><CODE>-g</CODE>
<DD>
If this switch is set, information is output only for library-level
entities, ignoring local entities. The use of this switch may accelerate
<CODE>gnatfind</CODE> and <CODE>gnatxref</CODE>.

<DT><CODE>-IDIR</CODE>
<DD>
Equivalent to <SAMP>`-aODIR -aIDIR'</SAMP>.

<DT><CODE>-pFILE</CODE>
<DD>
Specify a project file (see section <A HREF="gnat_ug.html#SEC97">Project files</A>) to use.
By default, <CODE>gnatxref</CODE> and <CODE>gnatfind</CODE> will try to locate a
project file in the current directory.

If a project file is either specified or found by the tools, then the content
of the source directory and object directory lines are added as if they
had been specified respectively by <SAMP>`-aI'</SAMP> and
<SAMP>`-aO'</SAMP>.

<DT><CODE>-r</CODE>
<DD>
By default, <CODE>gnatfind</CODE> will output only the information about the
declaration, body or type completion of the entities. If this switch is
set, the <CODE>gnatfind</CODE> will locate every reference to the entities in
the files specified on the command line (or in every file in the search
path if no file is given on the command line).

<DT><CODE>-s</CODE>
<DD>
If this switch is set, then <CODE>gnatfind</CODE> will output the content
of the Ada source file lines were the entity was found.

</DL>

<P>
All these switches may be in any order on the command line, and may even
appear after the file names. They need not be separated by spaces, thus
you can say <SAMP>`gnatxref -ag'</SAMP> instead of
<SAMP>`gnatxref -a -g'</SAMP>.

</P>
<P>
As stated previously, gnatfind will search in every directory in the
search path. You can force it to look only in the current directory if
you specify <CODE>*</CODE> at the end of the command line.

</P>


<H2><A NAME="SEC97" HREF="gnat_ug_toc.html#TOC97">Project files</A></H2>

<P>
The project files allows a programmer to specify how to compile its
application, where to find sources,... These files are used primarily by
the Emacs Ada mode, but they can also be used by the two tools
<CODE>gnatxref</CODE> and <CODE>gnatfind</CODE>.

</P>
<P>
A project file name must end with <TT>`.adp'</TT>. If a single one is
present in the current directory, then <CODE>gnatxref</CODE> and <CODE>gnatfind</CODE> will
extract the information from it. If multiple project files are found, none of
them is read, and you have to use the <SAMP>`-p'</SAMP> switch to specify the one
you want to use.

</P>
<P>
The following lines can be included, even though most of them have default
values which can be used in most cases.
The lines can be entered in any order in the file.
Except for <SAMP>`src_dir'</SAMP> and <SAMP>`obj_dir'</SAMP>, you can only have one instance of
each line. If you have multiple instances, only the last one is taken into
account.

</P>
<DL COMPACT>

<DT><SAMP>`src_dir=DIR         [default: "./"]'</SAMP>
<DD>
specifies a directory where to look for source files. Multiple src_dir lines
can be specified and they will be searched in the order they
are specified.

<DT><SAMP>`obj_dir=DIR         [default: "./"]'</SAMP>
<DD>
specifies a directory where to look for object and library files. Multiple
obj_dir lines can be specified and they will be searched in the order they
are specified

<DT><SAMP>`comp_opt=SWITCHES   [default: ""]'</SAMP>
<DD>
creates a variable which can be referred to subsequently by using
the <SAMP>`${comp_opt}'</SAMP> notation. This is intended to store the default
switches given to <TT>`gnatmake'</TT> and <TT>`gcc'</TT>.

<DT><SAMP>`bind_opt=SWITCHES   [default: ""]'</SAMP>
<DD>
creates a variable which can be referred to subsequently by using
the <SAMP>`${bind_opt}'</SAMP> notation. This is intended to store the default
switches given to <TT>`gnatbind'</TT>.

<DT><SAMP>`link_opt=SWITCHES   [default: ""]'</SAMP>
<DD>
creates a variable which can be referred to subsequently by using
the <SAMP>`${link_opt}'</SAMP> notation. This is intended to store the default
switches given to <TT>`gnatlink'</TT>.

<DT><SAMP>`main=EXECUTABLE     [default: ""]'</SAMP>
<DD>
specifies the name of the executable for the application. This variable can
be referred to in the following lines by using the <SAMP>`${main}'</SAMP> notation.

<DT><SAMP>`comp_cmd=COMMAND    [default: "gcc -c -I${src_dir} -g -gnatq"]'</SAMP>
<DD>
specifies the command used to compile a single file in the application.

<DT><SAMP>`make_cmd=COMMAND    [default: "gnatmake ${main} -aI${src_dir} -aO${obj_dir} -g -gnatq -cargs ${comp_opt} -bargs ${bind_opt} -largs ${link_opt}"]'</SAMP>
<DD>
specifies the command used to recompile the whole application.

<DT><SAMP>`run_cmd=COMMAND     [default: "${main}"]'</SAMP>
<DD>
specifies the command used to run the application.

<DT><SAMP>`debug_cmd=COMMAND   [default: "gdb ${main}"]'</SAMP>
<DD>
specifies the command used to debug the application

</DL>

<P>
<CODE>gnatxref</CODE> and <CODE>gnatfind</CODE> only take into account the <SAMP>`src_dir'</SAMP>
and <SAMP>`obj_dir'</SAMP> lines, and ignore the others.

</P>


<H2><A NAME="SEC98" HREF="gnat_ug_toc.html#TOC98">Regular expressions in gnatfind and gnatxref</A></H2>

<P>
As specified in the section about <CODE>gnatfind</CODE>, the pattern can be a
regular expression. Actually, there are to set of regular expressions
which are recognized by the program :

</P>
<DL COMPACT>

<DT><SAMP>`globbing patterns'</SAMP>
<DD>
These are the most usual regular expression. They are the same that you
generally used in a Unix shell command line, or in a DOS session.

Here is a more formal grammar :

<PRE>
   regexp ::= term
   term   ::= elmt            -- matches elmt
   term   ::= elmt elmt       -- concatenation (elmt then elmt)
   term   ::= *               -- any string of 0 or more characters
   term   ::= ?               -- matches any character
   term   ::= [char {char}] -- matches any character listed
   term   ::= [char - char]   -- matches any character in range
</PRE>

<DT><SAMP>`full regular expression'</SAMP>
<DD>
The second set of regular expressions is much more powerful. This is the
type of regular expressions recognized by utilities such a <TT>`grep'</TT>.

The following is the form of a regular expression, expressed in Ada
reference manual style BNF is as follows


<PRE>
   regexp ::= term {| term} -- alternation (term or term ...)

   term ::= item {item}     -- concatenation (item then item)

   item ::= elmt              -- match elmt
   item ::= elmt *            -- zero or more elmt's
   item ::= elmt +            -- one or more elmt's
   item ::= elmt ?            -- matches elmt or nothing
   elmt ::= nschar            -- matches given character
   elmt ::= [nschar {nschar}]   -- matches any character listed
   elmt ::= [^ nschar {nschar}] -- matches any character not listed
   elmt ::= [char - char]     -- matches chars in given range
   elmt ::= \ char            -- matches given character
   elmt ::= .                 -- matches any single character
   elmt ::= ( regexp )        -- parens used for grouping

   char ::= any character, including special characters
   nschar ::= any character except ()[].*+?^
</PRE>

Following are a few examples :

<DL COMPACT>

<DT><SAMP>`abcde|fghi'</SAMP>
<DD>
will match any of the two strings 'abcde' and 'fghi'.

<DT><SAMP>`abc*d'</SAMP>
<DD>
will match any string like 'abd', 'abcd', 'abccd', 'abcccd', and so on

<DT><SAMP>`[a-z]+'</SAMP>
<DD>
will match any string which has only lower-case characters in it (and at
least one character

</DL>
</DL>



<H2><A NAME="SEC99" HREF="gnat_ug_toc.html#TOC99">Examples of <CODE>gnatxref</CODE> usage</A></H2>



<H3><A NAME="SEC100" HREF="gnat_ug_toc.html#TOC100">General usage</A></H3>

<P>
For the following examples, we will consider the following units :

</P>

<PRE>
   main.ads:
   1: <B>with</B> Bar;
   2: <B>package</B> Main <B>is</B>
   3:     <B>procedure</B> Foo (B : <B>in</B> Integer);
   4:     C : Integer;
   5: <B>private</B>
   6:     D : Integer;
   7: <B>end</B> Main;

   main.adb:
   1: <B>package body</B> Main <B>is</B>
   2:     <B>procedure</B> Foo (B : <B>in</B> Integer) <B>is</B>
   3:     <B>begin</B>
   4:        C := B;
   5:        D := B;
   6:        Bar.Print (B);
   7:        Bar.Print (C);
   8:     <B>end</B> Foo;
   9: <B>end</B> Main;

   bar.ads:
   1: <B>package</B> Bar <B>is</B>
   2:     <B>procedure</B> Print (B : Integer);
   3: <B>end</B> bar;
</PRE>

<DL COMPACT>

The first thing to do is to recompile your application (for instance, in
that case just by doing a <SAMP>`gnatmake main'</SAMP>, so that GNAT generates
the cross-referencing information.
You can then issue any of the following commands:

<DT><CODE>gnatxref main.adb</CODE>
<DD>
<CODE>gnatxref</CODE> generates cross-reference information for main.adb
and every unit 'with'ed by main.adb.

The output would be:

<PRE>
B                                                      Type: Integer
  Decl: bar.ads           2:22
B                                                      Type: Integer
  Decl: main.ads          3:20
  Body: main.adb          2:20
  Ref:  main.adb          4:13     5:13     6:19
Bar                                                    Type: Unit
  Decl: bar.ads           1:9
  Ref:  main.adb          6:8      7:8
       main.ads           1:6
C                                                      Type: Integer
  Decl: main.ads          4:5
  Modi: main.adb          4:8
  Ref:  main.adb          7:19
D                                                      Type: Integer
  Decl: main.ads          6:5
  Modi: main.adb          5:8
Foo                                                    Type: Unit
  Decl: main.ads          3:15
  Body: main.adb          2:15
Main                                                    Type: Unit
  Decl: main.ads          2:9
  Body: main.adb          1:14
Print                                                   Type: Unit
  Decl: bar.ads           2:15
  Ref:  main.adb          6:12     7:12
</PRE>

that is the entity <CODE>Main</CODE> is declared in main.ads, line 2, column 9,
its body is in main.adb, line 1, column 14 and is not referenced any where.

The entity <CODE>Print</CODE> is declared in bar.ads, line 2, column 15 and it
it referenced in main.adb, line 6 column 12 and line 7 column 12.

<DT><CODE>gnatxref package1.adb package2.ads</CODE>
<DD>
<CODE>gnatxref</CODE> will generates cross-reference information for
package1.adb, package2.ads and any other package 'with'ed by any
of these.

</DL>



<H3><A NAME="SEC101" HREF="gnat_ug_toc.html#TOC101">Using gnatxref with vi</A></H3>

<P>
<CODE>gnatxref</CODE> can generate a tags file output, which can be used
directly from <TT>`vi'</TT>. Note that the standard version of <TT>`vi'</TT>
will not work properly with overloaded symbols. Consider using another
free implementation of <TT>`vi'</TT>, such as <TT>`vim'</TT>.

</P>

<PRE>
   $ gnatxref -v gnatfind.adb &#62; tags
</PRE>

<P>
will generate the tags file for <CODE>gnatfind</CODE> itself (if the sources
are in the search path!).

</P>
<P>
From <TT>`vi'</TT>, you can then use the command <SAMP>`:tag <I>entity</I>'</SAMP>
(replacing <I>entity</I> by whatever you are looking for), and vi will
display a new file with the corresponding declaration of entity.

</P>



<H2><A NAME="SEC102" HREF="gnat_ug_toc.html#TOC102">Examples of <CODE>gnatfind</CODE> usage</A></H2>

<DL COMPACT>

<DT><CODE>gnatfind -f xyz:main.adb</CODE>
<DD>
Find declarations for all entities xyz referenced at least once in
main.adb.  The references are search in every library file in the search
path.

The directories will be printed as well (as the <SAMP>`-f'</SAMP>
switch is set)

The output will look like:

<PRE>
   directory/main.ads:106:14: xyz &#60;= declaration
   directory/main.adb:24:10: xyz &#60;= body
   directory/foo.ads:45:23: xyz &#60;= declaration
</PRE>

that is to say, one of the entities xyz found in main.adb is declared at
line 12 of main.ads (and its body is in main.adb), and another one is
declared at line 45 of foo.ads

<DT><CODE>gnatfind -fs xyz:main.adb</CODE>
<DD>
This is the same command as the previous one, instead <CODE>gnatfind</CODE> will
display the content of the Ada source file lines.

The output will look like:


<PRE>
   directory/main.ads:106:14: xyz &#60;= declaration
      procedure xyz;
   directory/main.adb:24:10: xyz &#60;= body
      procedure xyz is
   directory/foo.ads:45:23: xyz &#60;= declaration
      xyz : Integer;
</PRE>

This can make it easier to find exactly the location your are looking
for.

<DT><CODE>gnatfind -r "*x*":main.ads:123 foo.adb</CODE>
<DD>
Find references to all entities containing an x that are
referenced on line 123 of main.ads.
The references will be searched only in main.adb and foo.adb.

<DT><CODE>gnatfind main.ads:123</CODE>
<DD>
Find declarations and bodies for all entities that are referenced on
line 123 of main.ads.

This is the same as <CODE>gnatfind "*":main.adb:123</CODE>.

<DT><CODE>gnatfind mydir/main.adb:123:45</CODE>
<DD>
Find the declaration for the entity referenced at column 45 in
line 123 of file main.adb in directory mydir. Note that it
is usual to omit the identifier name when the column is given,
since the column position identifies a unique reference.

The column has to be the beginning of the identifier, and should not
point to any character in the middle of the identifier.

</DL>



<H1><A NAME="SEC103" HREF="gnat_ug_toc.html#TOC103">File Name Krunching Using <CODE>gnatkr</CODE></A></H1>
<P>
<A NAME="IDX281"></A>

</P>
<P>
This chapter discusses the method used by the compiler to shorten
the default file names chosen for Ada units so that they do not
exceed the maximum length permitted. It also describes the
<CODE>gnatkr</CODE> utility that can be used to determine the result of
applying this shortening.

<UL>
<LI><A HREF="gnat_ug.html#SEC104">About gnatkr</A>
<LI><A HREF="gnat_ug.html#SEC105">Using gnatkr</A>
<LI><A HREF="gnat_ug.html#SEC106">Krunching Method</A>
<LI><A HREF="gnat_ug.html#SEC107">Examples of gnatkr Usage</A>
</UL>



<H2><A NAME="SEC104" HREF="gnat_ug_toc.html#TOC104">About <CODE>gnatkr</CODE></A></H2>

<P>
The default file naming rule in GNAT
is that the file name must be derived from
the unit name. The exact default rule is as follows:

<UL>
<LI>

Take the unit name and replace all dots by hyphens.
<LI>

If such a replacement occurs in the
second character position of a name, and the first character is
a, g, s, or i then replace the dot by the character
~ (tilde)
instead of a minus.
</UL>

<P>
The reason for this exception is to avoid clashes
with the standard names for children of System, Ada, Interfaces,
and GNAT, which use the prefixes s- a- i- and g-
respectively.

</P>
<P>
The <CODE>-gnatk<VAR>nn</VAR></CODE>
switch of the compiler activates a "krunching"
circuit that limits file names to nn characters (where nn is a decimal
integer). For example, using OpenVMS,
where the maximum file name length is
39, the value of nn is usually set to 39, but if you want to generate
a set of files that would be usable if ported to a system with some
different maximum file length, then a different value can be specified.
The default value of 39 for OpenVMS need not be specified.

</P>
<P>
The <CODE>gnatkr</CODE> utility can be used to determine the krunched name for
a given file, when krunched to a specified maximum length.

</P>


<H2><A NAME="SEC105" HREF="gnat_ug_toc.html#TOC105">Using <CODE>gnatkr</CODE></A></H2>

<P>
The <CODE>gnatkr</CODE> command has the form

</P>

<PRE>
   $ gnatkr <VAR>name</VAR> [<VAR>length</VAR>]
</PRE>

<P>
<VAR>name</VAR> can be an Ada name with dots or the GNAT name of the unit,
where the dots representing child units or subunit are replaced by
hyphens. The only confusion arises if a name ends in <CODE>.ads</CODE> or
<CODE>.adb</CODE>.  <CODE>gnatkr</CODE> takes this to be an extension if there are
no other dots in the name and the whole name is in lowercase.

</P>
<P>
<VAR>length</VAR> represents the length of the krunched name. The default
when no argument is given is 8 characters. A length of zero stands for
unlimited, in other words do not chop except for system files which are
always 8.

</P>
<P>
The output is the krunched name. The output has an extension only if the
original argument was a file name with an extension.

</P>


<H2><A NAME="SEC106" HREF="gnat_ug_toc.html#TOC106">Krunching Method</A></H2>

<P>
The initial file name is determined by the name of the unit that the file
contains. The name is formed by taking the full expanded name of the
unit and replacing the separating dots with hyphens and
using lowercase
for all letters, except that a hyphen in the second character position is
replaced by a tilde if the first character is
a, i, g, or s.
The extension is <CODE>.ads</CODE> for a
specification and <CODE>.adb</CODE> for a body.
Krunching does not affect the extension, but the file name is shortened to
the specified length by following these rules:

</P>

<UL>
<LI>

The name is divided into segments separated by hyphens, tildes or
underscores and all hyphens, tildes, and underscores are
eliminated. If this leaves the name short enough, we are done.

<LI>

If the name is too long, the longest segment is located (left-most if there are two
of equal length), and shortened by dropping its last character. This is
repeated until the name is short enough.

As an example, consider the krunching of <TT>`our-strings-wide_fixed.adb'</TT>
to fit the name into 8 characters as required by some operating systems.


<PRE>
   our-strings-wide_fixed 22
   our strings wide fixed 19
   our string  wide fixed 18
   our strin   wide fixed 17
   our stri    wide fixed 16
   our stri    wide fixe  15
   our str     wide fixe  14
   our str     wid  fixe  13
   our str     wid  fix   12
   ou  str     wid  fix   11
   ou  st      wid  fix   10
   ou  st      wi   fix   9
   ou  st      wi   fi    8
   Final file name: oustwifi.adb
</PRE>

<LI>

The file names for all predefined units are always krunched to eight
characters. The krunching of these predefined units uses the following
special prefix replacements:

<DL COMPACT>

<DT><TT>`ada-'</TT>
<DD>
replaced by <TT>`a-'</TT>

<DT><TT>`gnat-'</TT>
<DD>
replaced by <TT>`g-'</TT>

<DT><TT>`interfaces-'</TT>
<DD>
replaced by <TT>`i-'</TT>

<DT><TT>`system-'</TT>
<DD>
replaced by <TT>`s-'</TT>
</DL>

These system files have a hyphen in the second character position.  That
is why normal user files replace such a character with a
tilde, to
avoid confusion with system file names.

As an example of this special rule, consider
<TT>`ada-strings-wide_fixed.adb'</TT>, which gets krunched as follows:


<PRE>
   ada-strings-wide_fixed 22
   a-  strings wide fixed 18
   a-  string  wide fixed 17
   a-  strin   wide fixed 16
   a-  stri    wide fixed 15
   a-  stri    wide fixe  14
   a-  str     wide fixe  13
   a-  str     wid  fixe  12
   a-  str     wid  fix   11
   a-  st      wid  fix   10
   a-  st      wi   fix   9
   a-  st      wi   fi    8
   Final file name: a-stwifi.adb
</PRE>

</UL>

<P>
Of course no file shortening algorithm can guarantee uniqueness over all
possible unit names, and if file name krunching is used then it is your
responsibility to ensure that no name clashes occur.  The utility
program <CODE>gnatkr</CODE> is supplied for conveniently determining the
krunched name of a file.

</P>


<H2><A NAME="SEC107" HREF="gnat_ug_toc.html#TOC107">Examples of <CODE>gnatkr</CODE> Usage</A></H2>


<PRE>
   $ gnatkr very_long_unit_name.ads      --&#62; velounna.ads
   $ gnatkr grandparent-parent-child.ads --&#62; grparchi.ads
   $ gnatkr Grandparent.Parent.Child     --&#62; grparchi
   $ gnatkr very_long_unit_name.ads/count=6    --&#62; vlunna.ads
   $ gnatkr very_long_unit_name.ads/count=0    --&#62; very_long_unit_name.ads
</PRE>



<H1><A NAME="SEC108" HREF="gnat_ug_toc.html#TOC108">Preprocessing Using <CODE>gnatprep</CODE></A></H1>
<P>
<A NAME="IDX282"></A>

</P>
<P>
The <CODE>gnatprep</CODE> utility provides
a simple preprocessing capability for Ada programs.
It is designed for use with GNAT, but is not dependent on any special
features of GNAT.

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC109">Using gnatprep</A>
<LI><A HREF="gnat_ug.html#SEC110">Switches for gnatprep</A>
<LI><A HREF="gnat_ug.html#SEC111">Form of definitions file</A>
<LI><A HREF="gnat_ug.html#SEC112">Form of input text for gnatprep</A>
</UL>



<H2><A NAME="SEC109" HREF="gnat_ug_toc.html#TOC109">Using <CODE>gnatprep</CODE></A></H2>

<P>
To call <CODE>gnatprep</CODE> use

</P>

<PRE>
   $ gnatprep [-bcrsu] [-Dsymbol=value] infile outfile [deffile]
</PRE>

<P>
where
<DL COMPACT>

<DT><CODE>infile</CODE>
<DD>
is the full name of the input file, which is an Ada source
file containing preprocessor directives.

<DT><CODE>outfile</CODE>
<DD>
is the full name of the output file, which is an Ada source
in standard Ada form. When used with GNAT, this file name will
normally have an ads or adb suffix.

<DT><CODE>deffile</CODE>
<DD>
is the full name of a text file containing definitions of
symbols to be referenced by the preprocessor. This argument is
optional, and can be replaced by the use of the <CODE>-D</CODE> switch.

<DT><CODE>switches</CODE>
<DD>
is an optional sequence of switches as described in the next section.
</DL>



<H2><A NAME="SEC110" HREF="gnat_ug_toc.html#TOC110">Switches for <CODE>gnatprep</CODE></A></H2>

<DL COMPACT>

<DT><CODE>-b</CODE>
<DD>
Causes both preprocessor lines and the lines deleted by
preprocessing to be replaced by blank lines in the output source file,
preserving line numbers in the output file.

<DT><CODE>-c</CODE>
<DD>
Causes both preprocessor lines and the lines deleted
by preprocessing to be retained in the output source as comments marked
with the special string "--! ". This option will result in line numbers
being preserved in the output file.

<DT><CODE>-Dsymbol=value</CODE>
<DD>
Defines a new symbol, associated with value. If no value is given on the
command line, then symbol is considered to be <CODE>True</CODE>. This switch
can be used in place of a definition file.

<DT><CODE>-r</CODE>
<DD>
Causes a <CODE>Source_Reference</CODE> pragma to be generated that
references the original input file, so that error messages will use
the file name of this original file. The use of this switch implies
that preprocessor lines are not to be removed from the file, so its
use will force <CODE>-b</CODE> mode if
<CODE>-c</CODE>
has not been specified explicitly.

Note that if the file to be preprocessed contains multiple units, then
it will be necessary to <CODE>gnatchop</CODE> the output file from
<CODE>gnatprep</CODE>. If a <CODE>Source_Reference</CODE> pragma is present
in the preprocessed file, it will be respected by
<CODE>gnatchop -r</CODE>
so that the final chopped files will correctly refer to the original
input source file for <CODE>gnatprep</CODE>.

<DT><CODE>-s</CODE>
<DD>
Causes a sorted list of symbol names and values to be
listed on the standard output file.

<DT><CODE>-u</CODE>
<DD>
Causes undefined symbols to be treated as having the value FALSE in the context
of a preprocessor test. In the absence of this option, an undefined symbol in
a <CODE>#if</CODE> or <CODE>#elsif</CODE> test will be treated as an error.

</DL>

<P>
Note: if neither <CODE>-b</CODE> nor <CODE>-c</CODE> is present,
then preprocessor lines and
deleted lines are completely removed from the output, unless -r is
specified, in which case -b is assumed.

</P>


<H2><A NAME="SEC111" HREF="gnat_ug_toc.html#TOC111">Form of definitions file</A></H2>

<P>
The definitions file contains lines of the form

</P>

<PRE>
   symbol := value
</PRE>

<P>
where symbol is an identifier, following normal Ada (case-insensitive)
rules for its syntax, and value is one of the following:

</P>

<UL>
<LI>

Empty, corresponding to a null substitution
<LI>

A string literal using normal Ada syntax
<LI>

Any sequence of characters from the set
(letters, digits, period, underline).
</UL>

<P>
Comment lines may also appear in the definitions file, starting with
the usual <CODE>--</CODE>,
and comments may be added to the definitions lines.

</P>


<H2><A NAME="SEC112" HREF="gnat_ug_toc.html#TOC112">Form of input text for <CODE>gnatprep</CODE></A></H2>

<P>
The input text may contain preprocessor conditional inclusion lines,
as well as general symbol substitution sequences.
The preprocessor conditional inclusion commands have the form

</P>

<PRE>
   #if <I>expression</I> [then]
      lines
   #elsif <I>expression</I> [then]
      lines
   #elsif <I>expression</I> [then]
      lines
   ...
   #else
      lines
   #end if;
</PRE>

<P>
In this example, <I>expression</I> is defined by the following grammar:

<PRE>
   <I>expression</I> ::=  &#60;symbol&#62;
   <I>expression</I> ::=  &#60;symbol&#62; = "&#60;value&#62;"
   <I>expression</I> ::=  &#60;symbol&#62; = &#60;symbol&#62;
   <I>expression</I> ::=  &#60;symbol&#62; 'Defined
   <I>expression</I> ::=  not <I>expression</I>
   <I>expression</I> ::=  <I>expression</I> and <I>expression</I>
   <I>expression</I> ::=  <I>expression</I> or <I>expression</I>
   <I>expression</I> ::=  <I>expression</I> and then <I>expression</I>
   <I>expression</I> ::=  <I>expression</I> or else <I>expression</I>
   <I>expression</I> ::=  ( <I>expression</I> )
</PRE>

<P>
For the first test (<I>expression</I> ::= &#60;symbol&#62;) the symbol must have
either the value true or false, that is to say the right-hand of the
symbol definition must be one of the (case-insensitive) literals
<CODE>True</CODE> or <CODE>False</CODE>.  If the value is true, then the
corresponding lines are included, and if the value is false, they are
excluded.

</P>
<P>
The test (<I>expression</I> ::= &#60;symbol&#62; <CODE>'Defined</CODE>) is true only if
the symbol has been defined in the definition file or by a <CODE>-D</CODE>
switch on the command line. Otherwise, the test is false.

</P>
<P>
The equality tests are case insensitive, as are all the preprocessor lines.

</P>
<P>
If the symbol referenced is not defined in the symbol definitions file,
then the effect depends on whether or not switch <CODE>-u</CODE>
is specified. If so, then the symbol is treated as if it had the value
false and the test fails. If this switch is not specified, then
it is an error to reference an undefined symbol. It is also an error to
reference a symbol that is defined with a value other than <CODE>True</CODE>
or <CODE>False</CODE>.

</P>
<P>
The use of the not operator inverts the sense of this logical test, so
that the lines are included only if the symbol is not defined.
The <CODE>then</CODE> keyword is optional as shown

</P>
<P>
The <CODE>#</CODE> must be in column one, but otherwise the format is free form.
Spaces or tabs may appear between the <CODE>#</CODE> and the keyword. The keywords
and the symbols are case insensitive as in normal Ada code. Comments
may be used on a preprocessor line, but other than that, no other
tokens may appear on a preprocessor line.
Any number of <CODE>elsif</CODE> clauses can be present, including none at all.
The <CODE>else</CODE> is optional, as in Ada.

</P>
<P>
The <CODE>#</CODE> marking the start of a preprocessor line must be the first
non-blank character on the line, i.e. it must be preceded only by
spaces or horizontal tabs.

</P>
<P>
Symbol substitution outside of preprocessor lines is obtained by using
the sequence

</P>

<PRE>
   $symbol
</PRE>

<P>
anywhere within a source line, except in a comment. The identifier
following the <CODE>$</CODE> must match one of the symbols defined in the symbol
definition file, and the result is to substitute the value of the
symbol in place of <CODE>$symbol</CODE> in the output file.

</P>



<H1><A NAME="SEC113" HREF="gnat_ug_toc.html#TOC113">The GNAT library browser <CODE>gnatls</CODE></A></H1>
<P>
<A NAME="IDX283"></A>
<A NAME="IDX284"></A>

</P>
<P>
<CODE>gnatls</CODE> is a tool that outputs information about compiled
units. It gives the relationship between objects, unit names and source
files. It can also be used to check the source dependencies of a unit
as well as various characteristics.

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC114">Running gnatls</A>
<LI><A HREF="gnat_ug.html#SEC115">Switches for gnatls</A>
<LI><A HREF="gnat_ug.html#SEC116">Examples of gnatls Usage</A>
</UL>



<H2><A NAME="SEC114" HREF="gnat_ug_toc.html#TOC114">Running <CODE>gnatls</CODE></A></H2>

<P>
The <CODE>gnatls</CODE> command has the form

</P>

<PRE>
   $ gnatls switches <VAR>object_or_ali_file</VAR>
</PRE>

<P>
The main argument is the list of object or <TT>`ali'</TT> files
(see section <A HREF="gnat_ug.html#SEC21">The Ada Library Information Files</A>)
for which information is requested.

</P>
<P>
In normal mode, without additional option, <CODE>gnatls</CODE> produces a
four-column listing. Each line represents information for a specific
object. The first column gives the full path of the object, the second
column gives the name of the principal unit in this object, the third
column gives the status of the source and the fourth column gives the
full path of the source representing this unit.
Here is a simple example of use:

</P>

<PRE>
   $ gnatls *.o
   ./demo1.o            demo1            DIF demo1.adb
   ./demo2.o            demo2             OK demo2.adb
   ./hello.o            h1                OK hello.adb
   ./instr-child.o      instr.child      MOK instr-child.adb
   ./instr.o            instr             OK instr.adb
   ./tef.o              tef              DIF tef.adb
   ./text_io_example.o  text_io_example   OK text_io_example.adb
   ./tgef.o             tgef             DIF tgef.adb
</PRE>

<P>
The first line can be interpreted as follows: the main unit which is
contained in
object file <TT>`demo1.o'</TT> is demo1, whose main source is in
<TT>`demo1.adb'</TT>. Furthermore, the version of the source used for the
compilation of demo1 has been modified (DIF). Each source file has a status
qualifier which can be:

</P>
<DL COMPACT>

<DT><CODE>OK (unchanged)</CODE>
<DD>
The version of the source file used for the compilation of the
specified unit corresponds exactly to the actual source file.

<DT><CODE>MOK (slightly modified)</CODE>
<DD>
The version of the source file used for the compilation of the
specified unit differs from the actual source file but not enough to
require recompilation.  If you use gnatmake with the qualifier
<CODE>-m (minimal recompilation)</CODE>, a file marked
MOK will not be recompiled.

<DT><CODE>DIF (modified)</CODE>
<DD>
No version of the source found on the path corresponds to the source
used to build this object.

<DT><CODE>??? (file not found)</CODE>
<DD>
No source file was found for this unit.

<DT><CODE>HID (hidden,  unchanged version not first on PATH)</CODE>
<DD>
The version of the source that corresponds exactly to the source used
for compilation has been found on the path but it is hidden by another
version of the same source that has been modified.

</DL>



<H2><A NAME="SEC115" HREF="gnat_ug_toc.html#TOC115">Switches for <CODE>gnatls</CODE></A></H2>

<P>
<CODE>gnatls</CODE> recognizes the following switches:

</P>
<DL COMPACT>

<DT><CODE>-a</CODE>
<DD>
<A NAME="IDX285"></A>
Consider all units, including those of the predefined Ada library.
Especially useful with <CODE>-d</CODE>.

<DT><CODE>-d</CODE>
<DD>
<A NAME="IDX286"></A>
List sources from which specified units depend on.

<DT><CODE>-h</CODE>
<DD>
<A NAME="IDX287"></A>
Output the list of options.

<DT><CODE>-o</CODE>
<DD>
<A NAME="IDX288"></A>
Only output information about object files.

<DT><CODE>-s</CODE>
<DD>
<A NAME="IDX289"></A>
Only output information about source files.

<DT><CODE>-u</CODE>
<DD>
<A NAME="IDX290"></A>
Only output information about compilation units.

<DT><CODE>-aO<VAR>dir</VAR></CODE>
<DD>
<DT><CODE>-aI<VAR>dir</VAR></CODE>
<DD>
<DT><CODE>-I<VAR>dir</VAR></CODE>
<DD>
<DT><CODE>-I-</CODE>
<DD>
<DT><CODE>-nostdinc</CODE>
<DD>
Source and Object path manipulation. Same meaning as the equivalent
$ gnatmake flags section <A HREF="gnat_ug.html#SEC69">Switches for <CODE>gnatmake</CODE></A>

<DT><CODE>-v</CODE>
<DD>
<A NAME="IDX291"></A>
Verbose mode. Output the complete source and object paths. Do not use
the default column layout but instead use long format giving as much as
information possible on each requested units, including special
characteristics such as:

<DL COMPACT>

<DT><CODE>Preelaborable</CODE>
<DD>
The unit is preelaborable in the Ada 95 sense.

<DT><CODE>No_Elab_Code</CODE>
<DD>
No elaboration code has been produced by the compiler for this unit.

<DT><CODE>Pure</CODE>
<DD>
The unit is pure in the Ada 95 sense.

<DT><CODE>Elaborate_Body</CODE>
<DD>
The unit contains a pragma Elaborate_Body.

<DT><CODE>Remote_Types</CODE>
<DD>
The unit contains a pragma Remote_Types.

<DT><CODE>Shared_Passive</CODE>
<DD>
The unit contains a pragma Shared_Passive.

<DT><CODE>Predefined</CODE>
<DD>
This unit is part of the predefined environment and cannot be modified
by the user.

<DT><CODE>Remote_Call_Interface</CODE>
<DD>
The unit contains a pragma Remote_Call_Interface.

</DL>
</DL>



<H2><A NAME="SEC116" HREF="gnat_ug_toc.html#TOC116">Example of <CODE>gnatls</CODE> Usage</A></H2>

<P>
Example of using the verbose switch. Note how the source and
object paths are affected by the -I switch.

</P>

<PRE>
   $ gnatls -v -I.. demo1.o

   GNATLS 3.10w (970212) Copyright 1999 Free Software Foundation, Inc.

   Source Search Path:
      &#60;Current_Directory&#62;
      ../
      /home/comar/local/adainclude/

   Object Search Path:
      &#60;Current_Directory&#62;
      ../
      /home/comar/local/lib/gcc-lib/mips-sni-sysv4/2.7.2/adalib/

   ./demo1.o
      Unit =&#62;
        Name   =&#62; demo1
        Kind   =&#62; subprogram body
        Flags  =&#62; No_Elab_Code
        Source =&#62; demo1.adb    modified
</PRE>

<P>
The following is an example of use of the dependency list.
Note the use of the -s switch
which gives a straight list of source files. This can be useful for
building specialized scripts.

</P>

<PRE>
   $ gnatls -d demo2.o
   ./demo2.o   demo2        OK demo2.adb
                            OK gen_list.ads
                            OK gen_list.adb
                            OK instr.ads
                            OK instr-child.ads

   $ gnatls -d -s -a demo1.o
   demo1.adb
   /home/comar/local/adainclude/ada.ads
   /home/comar/local/adainclude/a-finali.ads
   /home/comar/local/adainclude/a-filico.ads
   /home/comar/local/adainclude/a-stream.ads
   /home/comar/local/adainclude/a-tags.ads
   gen_list.ads
   gen_list.adb
   /home/comar/local/adainclude/gnat.ads
   /home/comar/local/adainclude/g-io.ads
   instr.ads
   /home/comar/local/adainclude/system.ads
   /home/comar/local/adainclude/s-exctab.ads
   /home/comar/local/adainclude/s-finimp.ads
   /home/comar/local/adainclude/s-finroo.ads
   /home/comar/local/adainclude/s-secsta.ads
   /home/comar/local/adainclude/s-stalib.ads
   /home/comar/local/adainclude/s-stoele.ads
   /home/comar/local/adainclude/s-stratt.ads
   /home/comar/local/adainclude/s-tasoli.ads
   /home/comar/local/adainclude/s-unstyp.ads
   /home/comar/local/adainclude/unchconv.ads
</PRE>



<H1><A NAME="SEC117" HREF="gnat_ug_toc.html#TOC117">Rebuilding the GNAT Library</A></H1>
<P>
<A NAME="IDX292"></A>

</P>
<P>
It may be useful to recompile the GNAT library in various contexts, the
most important one being the use of partition wide configuration pragmas
such as Normalize_Scalar. A special Makefile called
<CODE>Makefile.adalib</CODE> is provided to that effect and can be found in
the directory containing the GNAT library. The location of this
directory depends on how the GNAT environment has been installed and can
be located with the command

</P>

<PRE>
   $ gnatls -v
</PRE>

<P>
The last line of the Object Search Path usually contains the
gnat library. This Makefile contains its own documentation and in
particular the set of instructions needed to rebuild a new library and
to use it.

</P>



<H1><A NAME="SEC118" HREF="gnat_ug_toc.html#TOC118">Finding memory problems with <CODE>gnatmem</CODE></A></H1>
<P>
<A NAME="IDX293"></A>

</P>
<P>
<CODE>gnatmem</CODE>, is a tool that monitors dynamic allocation and
deallocation activity in a program, and displays information about
incorrect deallocations and possible sources of memory leaks. Gnatmem
provides three type of information:

<UL>
<LI>

General information concerning memory management, such as the total
number of allocations and deallocations, the amount of allocated
memory and the high water mark, i.e. the largest amount of allocated
memory in the course of program execution.

<LI>

Backtraces for all incorrect deallocations, that is to say deallocations
which do not correspond to a valid allocation.

<LI>

Information on each allocation that is potentially the origin of a memory
leak.
</UL>


<UL>
<LI><A HREF="gnat_ug.html#SEC119">Running gnatmem</A>
<LI><A HREF="gnat_ug.html#SEC120">Switches for gnatmem</A>
<LI><A HREF="gnat_ug.html#SEC121">Examples of gnatmem Usage</A>
<LI><A HREF="gnat_ug.html#SEC122">Implementation note</A>
</UL>



<H2><A NAME="SEC119" HREF="gnat_ug_toc.html#TOC119">Running <CODE>gnatmem</CODE></A></H2>

<P>
The <CODE>gnatmem</CODE> command has the form

</P>

<PRE>
   $ gnatmem [n] [-o file] user_program [program_arg]*
or
   $ gnatmem [n] -i file
</PRE>

<P>
Gnatmem must be supplied with the executable to examine, followed by its
run-time inputs. For example, if a program is executed with the command:

<PRE>
   $ my_program arg1 arg2
</PRE>

<P>
then it can be run under <CODE>gnatmem</CODE> control using the command:

<PRE>
   $ gnatmem my_program arg1 arg2
</PRE>

<P>
The program is transparently executed under the control of the debugger
section <A HREF="gnat_ug.html#SEC149">The GNAT Debugger GDB</A>. This does not affect the behavior
of the program, except for sensitive real-time programs. When the program
has completed execution, <CODE>gnatmem</CODE> outputs a report containing general
allocation/deallocation information and potential memory leak.
For better results, the user program should be compiled with
debugging options section <A HREF="gnat_ug.html#SEC35">Switches for <CODE>gcc</CODE></A>.

</P>
<P>
Here is a simple example of use:

</P>
<P>
*************** debut cc

<PRE>
   $ gnatmem test_gm

   Global information
   ------------------
      Total number of allocations        :  45
      Total number of deallocations      :   6
      Final Water Mark (non freed mem)   :  11.29 Kilobytes
      High Water Mark                    :  11.40 Kilobytes

   .
   .
   .
   Allocation Root # 2
   -------------------
    Number of non freed allocations    :  11
    Final Water Mark (non freed mem)   :   1.16 Kilobytes
    High Water Mark                    :   1.27 Kilobytes
    Backtrace                          :
      test_gm.adb:23 test_gm.alloc
   .
   .
   .
</PRE>

<P>
The first block of output give general information. In this case, the
Ada construct "new" was executed 45 times, and only 6 calls to an
unchecked deallocation routine occurred.

</P>
<P>
Subsequent paragraphs display  information on all allocation roots.
An allocation
root is a specific point in the execution of the program that generates some
dynamic allocation, such as a "new" construct. This root is represented
by an execution backtrace (or subprogram call stack). By default the
backtrace depth for allocations roots is 1, so that a root corresponds
exactly to a source location. The backtrace can be made deeper, to make
the root more specific.

</P>


<H2><A NAME="SEC120" HREF="gnat_ug_toc.html#TOC120">Switches for <CODE>gnatmem</CODE></A></H2>

<P>
<CODE>gnatmem</CODE> recognizes the following switches:

</P>
<DL COMPACT>

<DT><CODE><CODE>-q</CODE></CODE>
<DD>
<A NAME="IDX294"></A>
Quiet. Gives the minimum output needed to identify the origin of the
memory leaks. Omit statistical information.

<DT><CODE><CODE>n</CODE></CODE>
<DD>
<A NAME="IDX295"></A>
N is an integer literal (usually between 1 and 10) which controls the
depth of the backtraces defining allocation root. The default value for
N is 1. The deeper the backtrace, the more precise the localization of
the root. Note that the total number of roots can depend on this
parameter.

<DT><CODE><CODE>-o file</CODE></CODE>
<DD>
<A NAME="IDX296"></A>
Direct the gdb output to the specified file. The gdb script used
to generate this output is also saved in the file <TT>`gnatmem.tmp'</TT>.

<DT><CODE><CODE>-i file</CODE></CODE>
<DD>
<A NAME="IDX297"></A>
Do the <CODE>gnatmem</CODE>
processing starting from <CODE>file</CODE> which has been generated
by a previous call to <CODE>gnatmem</CODE>
with the -o switch. This is useful for
post mortem processing.

</DL>



<H2><A NAME="SEC121" HREF="gnat_ug_toc.html#TOC121">Example of <CODE>gnatmem</CODE> Usage</A></H2>

<P>
The first example shows the use of <CODE>gnatmem</CODE>
on a simple leaking program.
Suppose that we have the following Ada program:

</P>

<PRE>
   <B>with</B> Unchecked_Deallocation;
   <B>procedure</B> Test_Gm <B>is</B>

      <B>type</B> T <B>is array</B> (1..1000) <B>of</B> Integer;
      <B>type</B> Ptr <B>is access</B> T;
      <B>procedure</B> Free <B>is new</B> Unchecked_Deallocation (T, Ptr);
      A : Ptr;

      <B>procedure</B> My_Alloc <B>is</B>
      <B>begin</B>
         A := <B>new</B> T;
      <B>end</B> My_Alloc;

      <B>procedure</B> My_DeAlloc <B>is</B>
         B : Ptr := A;
      <B>begin</B>
         Free (B);
      <B>end</B> My_DeAlloc;

   <B>begin</B>
      My_Alloc;
      <B>for</B> I <B>in</B> 1 .. 5 <B>loop</B>
         <B>for</B> J <B>in</B> I .. 5 <B>loop</B>
            My_Alloc;
         <B>end loop</B>;
         My_Dealloc;
      <B>end loop</B>;
   <B>end</B>;
</PRE>

<P>
The program needs to be compiled with debugging option:

</P>

<PRE>
   $ gnatmake -g test_gm
</PRE>

<P>
<CODE>gnatmem</CODE> is invoked simply with

<PRE>
   $ gnatmem test_gm
</PRE>

<P>
which produces the following output:

</P>

<PRE>
   Global information
   ------------------
      Total number of allocations        :  18
      Total number of deallocations      :   5
      Final Water Mark (non freed mem)   :  53.00 Kilobytes
      High Water Mark                    :  56.90 Kilobytes

   Allocation Root # 1
   -------------------
    Number of non freed allocations    :  11
    Final Water Mark (non freed mem)   :  42.97 Kilobytes
    High Water Mark                    :  46.88 Kilobytes
    Backtrace                          :
      test_gm.adb:11 test_gm.my_alloc

   Allocation Root # 2
   -------------------
    Number of non freed allocations    :   1
    Final Water Mark (non freed mem)   :  10.02 Kilobytes
    High Water Mark                    :  10.02 Kilobytes
    Backtrace                          :
      s-secsta.adb:81 system.secondary_stack.ss_init

   Allocation Root # 3
   -------------------
    Number of non freed allocations    :   1
    Final Water Mark (non freed mem)   :  12 Bytes
    High Water Mark                    :  12 Bytes
    Backtrace                          :
      s-secsta.adb:181 system.secondary_stack.ss_init
</PRE>

<P>
Note that the GNAT run time contains itself a certain number of
allocations that have no  corresponding deallocation,
as shown here for root #2 and root
#1. This is a normal behavior when the number of non freed allocations
is one, it locates dynamic data structures that the run time needs for
the complete lifetime of the program. Note also that there is only one
allocation root in the user program with a single line back trace:
test_gm.adb:11 test_gm.my_alloc, whereas a careful analysis of the
program shows that 'My_Alloc' is called at 2 different points in the
source (line 21 and line 24). If those two allocation roots need to be
distinguished, the backtrace depth parameter can be used:

</P>

<PRE>
   $ gnatmem 3 test_gm
</PRE>

<P>
which will give the following output:

</P>

<PRE>
   Global information
   ------------------
      Total number of allocations        :  18
      Total number of deallocations      :   5
      Final Water Mark (non freed mem)   :  53.00 Kilobytes
      High Water Mark                    :  56.90 Kilobytes

   Allocation Root # 1
   -------------------
    Number of non freed allocations    :  10
    Final Water Mark (non freed mem)   :  39.06 Kilobytes
    High Water Mark                    :  42.97 Kilobytes
    Backtrace                          :
      test_gm.adb:11 test_gm.my_alloc
      test_gm.adb:24 test_gm
      b_test_gm.c:52 main

   Allocation Root # 2
   -------------------
    Number of non freed allocations    :   1
    Final Water Mark (non freed mem)   :  10.02 Kilobytes
    High Water Mark                    :  10.02 Kilobytes
    Backtrace                          :
      s-secsta.adb:81  system.secondary_stack.ss_init
      s-secsta.adb:283 &#60;system__secondary_stack___elabb&#62;
      b_test_gm.c:33   adainit

   Allocation Root # 3
   -------------------
    Number of non freed allocations    :   1
    Final Water Mark (non freed mem)   :   3.91 Kilobytes
    High Water Mark                    :   3.91 Kilobytes
    Backtrace                          :
      test_gm.adb:11 test_gm.my_alloc
      test_gm.adb:21 test_gm
      b_test_gm.c:52 main

   Allocation Root # 4
   -------------------
    Number of non freed allocations    :   1
    Final Water Mark (non freed mem)   :  12 Bytes
    High Water Mark                    :  12 Bytes
    Backtrace                          :
      s-secsta.adb:181 system.secondary_stack.ss_init
      s-secsta.adb:283 &#60;system__secondary_stack___elabb&#62;
      b_test_gm.c:33   adainit
</PRE>

<P>
The allocation root #1 of the first example has been split in 2 roots #1
and #3 thanks to the more precise associated backtrace.

</P>


<H2><A NAME="SEC122" HREF="gnat_ug_toc.html#TOC122">Implementation note</A></H2>

<P>
<CODE>gnatmem</CODE> executes the user program under the control of <CODE>gdb</CODE> using
a script that sets breakpoints and gathers information on each dynamic
allocation and deallocation. The output of the script is then analyzed
by <CODE>gnatmem</CODE>
in order to locate memory leaks and their origin in the
program. Gnatmem works by recording each address returned by the
allocation procedure (<CODE>__gnat_malloc</CODE>)
along with the backtrace at the
allocation point. On each deallocation, the deallocated address is
matched with the corresponding allocation. At the end of the processing,
the unmatched allocations are considered potential leaks. All the
allocations associated with the same backtrace are grouped together and
form an allocation root. The allocation roots are then sorted so that
those with the biggest number of unmatched allocation are printed
first. A delicate aspect of this technique is to distinguish between the
data produced by the user program and the data produced by the gdb
script. Currently, on systems that allow probing the terminal, the gdb
command "tty" is used to force the program output to be redirected to the
current terminal while the gdb output is directed to a file or to a
pipe in order to be processed subsequently by <CODE>gnatmem</CODE>.

</P>



<H1><A NAME="SEC123" HREF="gnat_ug_toc.html#TOC123">ASIS-Based Tools</A></H1>

<P>
Some of the tools distributed with GNAT are based on the ASIS implementation
for GNAT (ASIS-for-GNAT). Binary executables for such tools do not require
ASIS-for-GNAT to be around and they have a command-line interface similar to
other GNAT tools. The main specific feature of ASIS-based tools is that they
process tree output files.

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC124">The ASIS Implementation for GNAT (ASIS-for-GNAT)</A>
<LI><A HREF="gnat_ug.html#SEC125">Tree Files</A>
</UL>



<H2><A NAME="SEC124" HREF="gnat_ug_toc.html#TOC124">The ASIS Implementation for GNAT (ASIS-for-GNAT)</A></H2>
<P>
<A NAME="IDX298"></A>
<A NAME="IDX299"></A>

</P>
<P>
The ASIS implementation for GNAT, called ASIS-for-GNAT, is the implementation
if the Ada Semantic Interface Specification (ASIS). It is a separate product
which is not included in the standard GNAT distribution. However, the
binary executables for tools created on top of ASIS-for-GNAT do not require
ASIS-for-GNAT installed on your system and they can be used for a standard
GNAT distribution along with other GNAT tools

</P>


<H2><A NAME="SEC125" HREF="gnat_ug_toc.html#TOC125">Tree Files</A></H2>
<P>
<A NAME="IDX300"></A>
<A NAME="IDX301"></A>

</P>
<P>
The ASIS implementation for GNAT is based on tree output files (or, simply,
tree files). A tree file stores a snapshot of the compiler internal data
structures in the very end of a successful compilation. It contains all the
syntactical and semantic information about the unit being compiled and all the
units upon which it depends semantically. ASIS-for-GNAT (and, therefore, any
tool based on its top) processes tree files, extracts this information from it
and converts it into the format prescribing by the ASIS definition.

</P>
<P>
To use some ASIS-based tools, a user should take care of producing the right
set of tree files for the tool, some other ASIS tools produce a needed set of
tree files themselves.

</P>
<P>
GNAT produces a tree file if -gnatt option is set when calling gcc. ASIS needs
tree files created in "compile-only" GNAT mode set by -gnatc gcc switch. Names
of the tree files are obtained by replacing 'd' with 't' in the extension of
the name of the source file being compiled.

</P>
<P>
Therefore, to produce a tree file for the body of a procedure Foo contained in
the source file named 'foo.adb', you can compile it using

</P>

<PRE>
   $ gcc -c -gnatc -gnatt foo.adb
</PRE>

<P>
and you will get the tree file named 'foo.atb' as a result of this
compilation.

</P>


<H1><A NAME="SEC126" HREF="gnat_ug_toc.html#TOC126">Creating Sample Bodies Using <CODE>gnatstub</CODE></A></H1>
<P>
<A NAME="IDX302"></A>

</P>
<P>
<CODE>gnatstub</CODE> creates body samples - that is, empty but compilable bodies for
library unit declarations.

</P>
<P>
<CODE>gnatstub</CODE> is an ASIS-based tool, but it creates a needed tree
file itself, so it can be considered as a usual command-line utility
program when using with GNAT.

</P>
<P>
To create a body sampler, <CODE>gnatstub</CODE> has to compile the library
unit declaration. Therefore, bodies can be created only for legal
library units. Moreover, if a library unit depends semantically upon
units located not only in the current directory, you have to provide
a source search path when calling gnatstub, see the description of
gnatstub switches below.

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC127">Running gnatstub</A>
<LI><A HREF="gnat_ug.html#SEC128">Switches for gnatstub</A>
</UL>



<H2><A NAME="SEC127" HREF="gnat_ug_toc.html#TOC127">Running <CODE>gnatstub</CODE></A></H2>

<P>
<CODE>gnatstub</CODE> has the command-line interface of the form

</P>

<PRE>
   $ gnatstub [switches] filename [directory]
</PRE>

<P>
where
<DL COMPACT>

<DT><CODE>filename</CODE>
<DD>
is the name of a source file containing a library unit declaration to
create a body for. This name should follow the GNAT file name
conventions. No crunching is allowed for this file name. The file
name may contain the path information.

<DT><CODE>directory</CODE>
<DD>
indicates the directory to place a sample body (default is the
current directory)

<DT><CODE>switches</CODE>
<DD>
is an optional sequence of switches as described in the next section
</DL>



<H2><A NAME="SEC128" HREF="gnat_ug_toc.html#TOC128">Switches for <CODE>gnatstub</CODE></A></H2>

<DL COMPACT>

<DT><CODE>-f</CODE>
<DD>
Replace an existing body file (if any) with a body sample. If the
destination directory already contains a file which name has a form
of the body file for the argument spec file, gnatstub replaces it
with the body sample if <CODE>-f</CODE> switch is set or leaves it intact
otherwise.

<DT><CODE>-hs</CODE>
<DD>
Put in body sample the comment header from the source of the library unit
declaration ("comment header" is all the comments preceding the compilation
unit).

<DT><CODE>-hg</CODE>
<DD>
Put in body sample a sample comment header

<DT><CODE>-IDIR</CODE>
<DD>
<DT><CODE>-I-</CODE>
<DD>
These switches have just the same meaning as in calls to gcc or
gnatmake. They are used to define the source search path in the call
to gcc issued by gnatstub to compile an argument source file to
create a tree file.

<DT><CODE>-i<VAR>n</VAR></CODE>
<DD>
(<VAR>n</VAR> is a decimal natural number). Sets the indentation level in the
generated body sample to n, '-i0' means "no indentation",
the default indentation is 3.

<DT><CODE>-k</CODE>
<DD>
Do not remove the tree file: as default, after creating the body
sampler gnatstub removes from the current directory the tree file
created for the argument source file. <CODE>-k</CODE> prevents deleting the
tree file.

<DT><CODE>-l<VAR>n</VAR></CODE>
<DD>
(<VAR>n</VAR> is a decimal positive number) Sets maximum line length in a
body sample to n, the default line length is 78.

<DT><CODE>-q</CODE>
<DD>
Quiet mode: gnatstub does not generate a confirmation when a body is
successfully created or a message when a body is not required for an
argument unit.

<DT><CODE>-r</CODE>
<DD>
Reuse the tree file (if any) instead of creating it: instead of
creating the tree file for the library unit declaration, gnatstub
tries to find it in the current directory and to use it for creating
a body. If the tree file is not found, no body is created. <CODE>-r</CODE>
also implies <CODE>-k</CODE>, whether or not
<CODE>-k</CODE> is set explicitly.

<DT><CODE>-t</CODE>
<DD>
Overwrite the existing tree file: if the current directory already
contains the file which, according to the GNAT file name rules should
be considered as a tree file for the argument source file, gnatstub
will refuse to create the tree file needed to create a body sampler,
unless <CODE>-t</CODE> option is set

<DT><CODE>-v</CODE>
<DD>
Verbose mode: gnatstub generates version information.

</DL>



<H1><A NAME="SEC129" HREF="gnat_ug_toc.html#TOC129">Minimizing Executables for Ada Programs Using <CODE>gnatelim</CODE></A></H1>
<P>
<A NAME="IDX303"></A>

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC130">About gnatelim</A>
<LI><A HREF="gnat_ug.html#SEC131">Eliminate pragma</A>
<LI><A HREF="gnat_ug.html#SEC132">Preparing Tree and Bind Files for gnatelim</A>
<LI><A HREF="gnat_ug.html#SEC133">Running gnatelim</A>
<LI><A HREF="gnat_ug.html#SEC134">Correcting the List of Eliminate Pragmas</A>
<LI><A HREF="gnat_ug.html#SEC135">Making your Executables smaller</A>
<LI><A HREF="gnat_ug.html#SEC136">Summary of the gnatelim Usage Cycle</A>
</UL>



<H2><A NAME="SEC130" HREF="gnat_ug_toc.html#TOC130">About <CODE>gnatelim</CODE></A></H2>

<P>
When a program shares a set of Ada
packages with other programs, it may happen that this program uses
only a fraction of the subprograms defined in these packages. The code
created for those unused subprograms increases the size of the executable.

</P>
<P>
<CODE>gnatelim</CODE> is a utility tracking unused subprograms in an Ada
program. Its output consists of a list of <CODE>Eliminate</CODE> pragmas
marking all the subprograms that are declared, but never called in a
given program. <CODE>Eliminate</CODE> is a GNAT-specific pragma, it is
described in the next section. By placing the list of
<CODE>Eliminate</CODE> pragmas in the GNAT configuration file
<TT>`gnat.adc'</TT> and recompiling your program, you may decrease the
size of its executable, because the compiler will not generate code
for those unused subprograms.

</P>
<P>
<CODE>gnatelim</CODE> is an ASIS-based tool, and it needs as its input data
a set of tree files representing all the components of a program to
process. It also needs a bind file for a main subprogram. (See
section <A HREF="gnat_ug.html#SEC132">Preparing Tree and Bind Files for <CODE>gnatelim</CODE></A> for full details)

</P>


<H2><A NAME="SEC131" HREF="gnat_ug_toc.html#TOC131"><CODE>Eliminate</CODE> pragma</A></H2>
<P>
<A NAME="IDX304"></A>

</P>
<P>
The syntax of Eliminate pragma is

</P>

<PRE>
   <B>pragma</B> Eliminate (Library_Unit_Name, Subprogram_Name);
</PRE>

<DL COMPACT>

<DT><CODE>Library_Unit_Name</CODE>
<DD>
full expanded Ada name of a library unit

<DT><CODE>Subprogram_Name</CODE>
<DD>
a simple or expanded name of a subprogram declared within this
compilation unit

</DL>

<P>
The effect of an Eliminate pragma placed in the GNAT configuration
file <TT>`gnat.adc'</TT> is:

</P>

<UL>

<LI>

If the subprogram denoted by <CODE>Subprogram_Name</CODE> is declared within
the library unit having <CODE>Library_Unit_Name</CODE> as its defining program
unit name, then the compiler will not generate code for this subprogram.
It applies to all overloaded subprograms denoted by
<CODE>Subprogram_Name</CODE>.

<LI>

If a subprogram mentioned in some <CODE>Eliminate</CODE> pragma as unused is
actually used (called) in a program, then the compiler will produce a
diagnosis in place where it is called.
</UL>



<H2><A NAME="SEC132" HREF="gnat_ug_toc.html#TOC132">Preparing Tree and Bind Files for <CODE>gnatelim</CODE></A></H2>

<P>
<CODE>gnatelim</CODE> can process only full Ada programs (partitions) and
it needs a set of tree files representing the whole program
(partition) to be presented in the current directory. It also needs a
bind file for the main subprogram of the program (partition) to be
presented in the current directory.

</P>
<P>
Let <CODE>Main_Prog</CODE> be the name of a main subprogram, and suppose
this subprogram is in a file named <TT>`main_prog.ads'</TT> or
<TT>`main_prog.adb'</TT>.

</P>
<P>
To create a minimal set of tree files covering the whole program, call
<CODE>gnatmake</CODE> for this program as follows:

</P>

<PRE>
   $ gnatmake -c -f -gnatc -gnatt Main_Prog
</PRE>

<P>
The <CODE>-c gnatmake</CODE> option turns off the bind and link phases,
which are impossible anyway, because sources are compiled with
<CODE>-gnatc</CODE> option, which turns off code generation.

</P>
<P>
 the <CODE>-f</CODE> gnatmake option is used to force
recompilation of all the needed sources.

</P>
<P>
To create a bind file for <CODE>gnatelim</CODE>, run <CODE>gnatbind</CODE> for
the main subprogram. <CODE>gnatelim</CODE> can work with either an Ada or a C
bind file, if both are present, it works with the Ada bind file.
To avoid problems with creating a consistent data for
<CODE>gnatelim</CODE>, it is advised to use the following procedure. It creates all
the data needed by <CODE>gnatelim</CODE> from scratch and therefore
guarantees their consistency:

</P>

<OL>
<LI>

creating a bind file:


<PRE>
   $ gnatmake -c Main_Prog
   $ gnatbind main_prog
</PRE>

<LI>

creating a set of tree files:


<PRE>
   $ gnatmake -f -c -gnatc -gnatt Main_Prog
</PRE>

</OL>

<P>
Note, that <CODE>gnatelim</CODE> needs neither object nor ALI files, so they
can be deleted at this stage.

</P>


<H2><A NAME="SEC133" HREF="gnat_ug_toc.html#TOC133">Running <CODE>gnatelim</CODE></A></H2>

<P>
gnatelim has the following command-line interface:

</P>

<PRE>
   $ gnatelim [options] name
</PRE>

<P>
<CODE>name</CODE> should be a full expanded Ada name of a main subprogram
of a program (partition).

</P>
<P>
gnatelim options:

</P>
<DL COMPACT>

<DT><CODE>-v</CODE>
<DD>
Verbose mode: gnatelim version information is printed (in the form of Ada
comments) to the standard output file. Various debugging information and
information reflecting some details of the analysis doing by gnatelim are
output to the standard error file.

<DT><CODE>-a</CODE>
<DD>
Will also indicate subprograms from the GNAT runtime that could be
eliminated.

<DT><CODE>-m</CODE>
<DD>
Will check if tree files are missing for an accurate result.
</DL>

<P>
<CODE>gnatelim</CODE> directs its output to the standard output,
so to produce a proper GNAT configuration file
<TT>`gnat.adc'</TT>, redirection can be used:

</P>

<PRE>
   $ gnatelim Main_Prog &#62; gnat.adc
</PRE>

<P>
or

</P>

<PRE>
   $ gnatelim Main_Prog &#62;&#62; gnat.adc
</PRE>

<P>
In order to append the gnatelim output to the existing contents of
<TT>`gnat.adc'</TT>.

</P>


<H2><A NAME="SEC134" HREF="gnat_ug_toc.html#TOC134">Correcting the List of Eliminate Pragmas</A></H2>

<P>
It may happen that <CODE>gnatelim</CODE> try to eliminate subprograms which
cannot really be eliminated because they are actually called in the
program although this only happens in very rare cases. In this case, the
compiler will generate an error message of the form:

</P>

<PRE>
   file.adb:106:07: cannot call eliminated subprogram "My_Prog"
</PRE>

<P>
You have to correct the <TT>`gnat.adc'</TT> file manually by suppressing
the faulty Eliminate pragmas. It is advised to recompile your program
from scratch after that, because you need a consistent
<TT>`gnat.adc'</TT> file during the complete compilation in order to get
an meaningful result.

</P>


<H2><A NAME="SEC135" HREF="gnat_ug_toc.html#TOC135">Making your Executables smaller</A></H2>

<P>
To get a smaller executable for your program, you have to recompile
the program completely, having the <TT>`gnat.adc'</TT> file with a set of
<CODE>Eliminate</CODE> pragmas created by <CODE>gnatelim</CODE> in your current
directory:

</P>

<PRE>
   $ gnatmake -f Main_Prog
</PRE>

<P>
(you will need <CODE>-f</CODE> option for gnatmake to
recompile everything
with the set of pragmas <CODE>Eliminate</CODE> you have got from
<CODE>gnatelim</CODE>).

</P>
<P>
Be aware that a set of <CODE>Eliminate</CODE> pragmas is specific to each
program. Therefore, it is not advised to merge sets of <CODE>Eliminate</CODE>
pragmas created for different programs in one <TT>`gnat.adc'</TT> file.

</P>


<H2><A NAME="SEC136" HREF="gnat_ug_toc.html#TOC136">Summary of the gnatelim Usage Cycle</A></H2>

<P>
Here is a summary of the steps to be taken in order to reduce the size of
your executables with <CODE>gnatelim</CODE>. You may use
other GNAT options to control the optimization level,
to produce the debugging information, to set search path, etc.

</P>

<OL>
<LI>

Produce a bind file and a set of tree files


<PRE>
   $ gnatmake -c Main_Prog
   $ gnatbind main_prog
   $ gnatmake -f -c -gnatc -gnatt Main_Prog
</PRE>

<LI>

Generate a list of <CODE>Eliminate</CODE> pragmas

<PRE>
   $ gnatelim Main_Prog &#62;[&#62;] gnat.adc
</PRE>

<LI>

Recompile the application


<PRE>
   $ gnatmake -f Main_Prog
</PRE>

</OL>



<H1><A NAME="SEC137" HREF="gnat_ug_toc.html#TOC137">Other Utility Programs</A></H1>

<P>
This chapter discusses some other utility programs available in the Ada
environment.

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC138">Using Other Utility Programs With GNAT</A>
<LI><A HREF="gnat_ug.html#SEC139">The gnatpsys Utility Program</A>
<LI><A HREF="gnat_ug.html#SEC140">The gnatpsta Utility Program</A>
<LI><A HREF="gnat_ug.html#SEC141">The External Symbol Naming Scheme of GNAT</A>
<LI><A HREF="gnat_ug.html#SEC142">Ada Mode for emacs</A>
<LI><A HREF="gnat_ug.html#SEC146">Converting Ada files to html using gnathtml</A>
<LI><A HREF="gnat_ug.html#SEC147">Installing gnathtml</A>
</UL>



<H2><A NAME="SEC138" HREF="gnat_ug_toc.html#TOC138">Using Other Utility Programs With GNAT</A></H2>

<P>
The object files generated by GNAT are in standard system format and in
particular the debugging information uses this format. This means
programs generated by GNAT can be used with existing utilities that
depend on these formats.

</P>
<P>
In general, any utility program that works with C will also often work with
Ada programs generated by GNAT. This includes software utilities such as
gprof (a profiling program), gdb (the FSF debugger), and utilities such
as Purify.

</P>


<H2><A NAME="SEC139" HREF="gnat_ug_toc.html#TOC139">The <CODE>gnatpsys</CODE> Utility Program</A></H2>

<P>
Many of the definitions in package System are implementation-dependent.
Furthermore, although the source of the package System is available
for inspection, it uses special attributes for parameterizing many of
the critical values, so the source is not informative for the casual user.

</P>
<P>
The <CODE>gnatpsys</CODE> utility is designed to deal with this situation.
It is an Ada program that dynamically determines the
values of all the relevant parameters in System, and prints them
out in the form of an Ada source listing for System, displaying all
the values of interest. This output is generated to
<TT>`stdout'</TT>.

</P>
<P>
To determine the value of any parameter in package System, simply
run <CODE>gnatpsys</CODE> with no qualifiers or arguments, and examine
the output. This is preferable to consulting documentation, because
you know that the values you are getting are the actual ones provided
by the executing system.

</P>


<H2><A NAME="SEC140" HREF="gnat_ug_toc.html#TOC140">The <CODE>gnatpsta</CODE> Utility Program</A></H2>

<P>
Many of the definitions in package Standard are implementation-dependent.
However, the source of this package does not exist as an Ada source
file, so these values cannot be determined by inspecting the source.
They can be determined by examining in detail the coding of
<TT>`cstand.adb'</TT> which creates the image of Standard in the compiler,
but this is awkward and requires a great deal of internal knowledge
about the system.

</P>
<P>
The <CODE>gnatpsta</CODE> utility is designed to deal with this situation.
It is an Ada program that dynamically determines the
values of all the relevant parameters in Standard, and prints them
out in the form of an Ada source listing for Standard, displaying all
the values of interest. This output is generated to
<TT>`stdout'</TT>.

</P>
<P>
To determine the value of any parameter in package Standard, simply
run <CODE>gnatpsta</CODE> with no qualifiers or arguments, and examine
the output. This is preferable to consulting documentation, because
you know that the values you are getting are the actual ones provided
by the executing system.

</P>


<H2><A NAME="SEC141" HREF="gnat_ug_toc.html#TOC141">The External Symbol Naming Scheme of GNAT</A></H2>

<P>
In order to interpret the output from GNAT, when using tools that are
originally intended for use with other languages, it is useful to
understand the conventions used to generate link names from the Ada
entity names.

</P>
<P>
All link names are in all lowercase letters. With the exception of library
procedure names, the mechanism used is simply to use the full expanded
Ada name with dots replaced by double underscores. For example, suppose
we have the following package spec:

</P>

<PRE>
   <B>package</B> QRS <B>is</B>
      MN : Integer;
   <B>end</B> QRS;
</PRE>

<P>
The variable <CODE>MN</CODE> has a full expanded Ada name of <CODE>QRS.MN</CODE>, so
the corresponding link name is <CODE>qrs__mn</CODE>.
<A NAME="IDX305"></A>
Of course if a <CODE>pragma Export</CODE> is used this may be overridden:

</P>

<PRE>
   <B>package</B> Exports <B>is</B>
      Var1 : Integer;
      <B>pragma</B> Export (Var1, C, External_Name =&#62; "var1_name");
      Var2 : Integer;
      <B>pragma</B> Export (Var2, C, Link_Name =&#62; "var2_link_name");
   <B>end</B> Exports;
</PRE>

<P>
In this case, the link name for <VAR>Var1</VAR> is <VAR>var1_name</VAR>, and the
link name for <VAR>Var2</VAR> is <VAR>var2_link_name</VAR>.

</P>
<P>
<A NAME="IDX306"></A>
One exception occurs for library level procedures. A potential ambiguity
arises between the required name <CODE>_main</CODE> for the C main program,
and the name we would otherwise assign to an Ada library level procedure
called <CODE>Main</CODE> (which might well not be the main program).

</P>
<P>
To avoid this ambiguity, we attach the prefix <CODE>_ada_</CODE> to such
names. So if we have a library level procedure such as

</P>

<PRE>
   <B>procedure</B> Hello (S : String);
</PRE>

<P>
the external name of this procedure will be <VAR>_ada_hello</VAR>.

</P>


<H2><A NAME="SEC142" HREF="gnat_ug_toc.html#TOC142">Ada Mode for <CODE>emacs</CODE></A></H2>

<P>
The Emacs mode for programming in Ada (both, Ada83 and Ada95) helps the
user in understanding existing code and facilitates writing new code.  It
furthermore provides some utility functions for easier integration of
standard Emacs features when programming in Ada.

</P>


<H2><A NAME="SEC143" HREF="gnat_ug_toc.html#TOC143">General features:</A></H2>


<UL>
<LI>

Full Integrated Development Environment :
  @itemize @bullet
  @item
  support of 'project files' for the configuration (directories,
  compilation options,...)

  @item
  compiling and stepping through error messages.

  @item
  running and debugging your applications within Emacs.
  @end itemize

<LI>

easy to use for beginners by pull-down menus,

<LI>

user configurable by many user-option variables.
</UL>



<H2><A NAME="SEC144" HREF="gnat_ug_toc.html#TOC144">Ada mode features that help understanding code:</A></H2>


<UL>
<LI>

functions for easy and quick stepping through Ada code,

<LI>

getting cross reference information for identifiers (e.g. find the
defining place by a keystroke),

<LI>

displaying an index menu of types and subprograms and move point to
the chosen one,

<LI>

automatic color highlighting of the various entities in Ada code.
</UL>



<H2><A NAME="SEC145" HREF="gnat_ug_toc.html#TOC145">Emacs support for writing Ada code:</A></H2>


<UL>
<LI>

switching between spec and body files with possible
autogeneration of body files,

<LI>

automatic formating of subprograms parameter lists.

<LI>

automatic smart indentation according to Ada syntax,

<LI>

automatic completion of identifiers,

<LI>

automatic casing of identifiers, keywords, and attributes,

<LI>

insertion of statement templates,

<LI>

filling comment paragraphs like filling normal text,
</UL>

<P>
For more information, please see See section <A HREF="gnat_ug.html#SEC142">Ada Mode for <CODE>emacs</CODE></A>.

</P>



<H2><A NAME="SEC146" HREF="gnat_ug_toc.html#TOC146">Converting Ada files to html using gnathtml</A></H2>

<P>
This <CODE>Perl</CODE> script allows Ada source files to be browsed using
standard Web browsers. For installation procedure, see the section
See section <A HREF="gnat_ug.html#SEC147">Installing gnathtml</A>.

</P>
<P>
Ada reserved keywords are highlighted in a bold font and Ada comments in
a blue font. Unless your program was compiled with the gcc <CODE>-gnatx</CODE>
switch to suppress the generation of cross-referencing information, user
defined variables and types will appear in a different color; you will
be able to click on any identifier and go to its declaration.

</P>
<P>
The command line is as follow:

<PRE>
   $ perl gnathtml.pl [switches] ada-files
</PRE>

<P>
You can pass it as many Ada files as you want. <CODE>gnathtml</CODE> will generate
an html file for every ada file, and a global file called <TT>`index.htm'</TT>.
This file is an index of every identifier defined in the files.

</P>
<P>
The available switches are the following ones :

</P>
<DL COMPACT>

<DT><CODE>-83</CODE>
<DD>
<A NAME="IDX307"></A>
Only the subset on the Ada 83 keywords will be highlighted, not the full
Ada 95 keywords set.

<DT><CODE>-cc <VAR>color</VAR></CODE>
<DD>
This options allows you to change the color used for comments. The default
value is green. The color argument can be any name accepted by html.

<DT><CODE>-d</CODE>
<DD>
<A NAME="IDX308"></A>
If the ada files depend on some other files (using for instance the
<CODE>with</CODE> command, the latter will also be converted to html.
Only the files in the user project will be converted to html, not the files
in the runtime library itself.

<DT><CODE>-D</CODE>
<DD>
This command is the same as -d above, but <CODE>gnathtml</CODE> will also look
for files in the runtime library, and generate html files for them.

<DT><CODE>-f</CODE>
<DD>
<A NAME="IDX309"></A>
By default, gnathtml will generate html links only for global entities
('with'ed units, global variables and types,...). If you specify the
<CODE>-f</CODE> on the command line, then links will be generated for local
entities too.

<DT><CODE>-l <VAR>number</VAR></CODE>
<DD>
<A NAME="IDX310"></A>
If this switch is provided and <VAR>number</VAR> is not 0, then <CODE>gnathtml</CODE>
will number the html files every <VAR>number</VAR> line.

<DT><CODE>-I <VAR>dir</VAR></CODE>
<DD>
<A NAME="IDX311"></A>
Specify a directory to search for library files (<TT>`.ali'</TT> files) and
source files. You can provide several -I switches on the command line,
and the directories will be parsed in the order of the command line.

<DT><CODE>-o <VAR>dir</VAR></CODE>
<DD>
<A NAME="IDX312"></A>
Specify the output directory for html files. By default, gnathtml will
saved the generated html files in a subdirectory named <TT>`html/'</TT>.

<DT><CODE>-p <VAR>file</VAR></CODE>
<DD>
<A NAME="IDX313"></A>
If you are using Emacs and the most recent Emacs Ada mode, which provides
a full Integrated Development Environment for compiling, checking,
running and debugging applications, you may be using <TT>`.adp'</TT> files
to give the directories where Emacs can find sources and object files.

Using this switch, you can tell gnathtml to use these files. This allows
you to get an html version of your application, even if it is spread
over multiple directories.

<DT><CODE>-sc <VAR>color</VAR></CODE>
<DD>
This options allows you to change the color used for symbol definitions.
The default value is red. The color argument can be any name accepted by html.

</DL>



<H2><A NAME="SEC147" HREF="gnat_ug_toc.html#TOC147">Installing gnathtml</A></H2>

<P>
<CODE>Perl</CODE> needs to be installed on your machine to run this script.
<CODE>Perl</CODE> is freely available for almost every architecture and
Operating System via the Internet.

</P>
<P>
On Unix systems, you  may want to modify  the  first line of  the script
<CODE>gnathtml</CODE>,  to explicitly  tell  the Operating  system  where Perl
is. The syntax of this line is :

<PRE>
   #!full_path_name_to_perl
</PRE>

<P>
Alternatively, you may run the script using the following command line:

</P>

<PRE>
   $ perl gnathtml.pl [switches] files
</PRE>



<H1><A NAME="SEC148" HREF="gnat_ug_toc.html#TOC148">Running and Debugging Ada Programs</A></H1>
<P>
<A NAME="IDX314"></A>

</P>
<P>
This chapter discusses how to debug Ada programs. An incorrect Ada program
may be handled in three ways by the GNAT compiler:

</P>

<OL>
<LI>

The illegality may be a violation of the static semantics of Ada. In
that case GNAT diagnoses the constructs in the program that are illegal.
It is then a straightforward matter for the user to modify those parts of
the program.

<LI>

The illegality may be a violation of the dynamic semantics of Ada. In
that case the program compiles and executes, but may generate incorrect
results, or may terminate abnormally with some exception.

<LI>

When presented with a program that contains convoluted errors, GNAT
itself may terminate abnormally without providing full diagnostics on
the incorrect user program.
</OL>


<UL>
<LI><A HREF="gnat_ug.html#SEC149">The GNAT Debugger GDB</A>
<LI><A HREF="gnat_ug.html#SEC150">Running GDB</A>
<LI><A HREF="gnat_ug.html#SEC151">Introduction to GDB Commands</A>
<LI><A HREF="gnat_ug.html#SEC152">Using Ada Expressions</A>
<LI><A HREF="gnat_ug.html#SEC153">Calling User-Defined Subprograms</A>
<LI><A HREF="gnat_ug.html#SEC154">Ada Exceptions</A>
<LI><A HREF="gnat_ug.html#SEC155">Ada Tasks</A>
<LI><A HREF="gnat_ug.html#SEC156">Debugging Generic Units</A>
<LI><A HREF="gnat_ug.html#SEC157">GNAT Abnormal Termination</A>
<LI><A HREF="gnat_ug.html#SEC158">Naming Conventions for GNAT Source Files</A>
<LI><A HREF="gnat_ug.html#SEC159">Getting Internal Debugging Information</A>
</UL>

<P>
<A NAME="IDX315"></A>
<A NAME="IDX316"></A>

</P>


<H2><A NAME="SEC149" HREF="gnat_ug_toc.html#TOC149">The GNAT Debugger GDB</A></H2>

<P>
GDB is a general purpose, platform-independent debugger that can be used to
debug mixed-language programs compiled with GCC, and in particular
is capable of debugging Ada programs compiled with GNAT. The latest
versions of GDB are Ada-aware and can handle complex Ada data structures.
The manual <CITE>Debugging with GDB</CITE>
contains full details on the usage of GDB, including a section on its usage
on programs. This manual should be consulted for full details. The section
that follows is a brief introduction to the philosophy and use of GDB.

</P>
<P>
When GNAT programs are compiled, the compiler optionally writes debugging
information into the generated object file, including information on
line numbers, and on declared types and variables. This information is
separate from the generated code. It makes the object files considerably
larger, but it does not add to the size of the actual executable that
will be loaded into memory, and has no impact on run-time performance. The
generation of debug information is triggered by the use of the
-g switch in the gcc or gnatmake command used to carry out
the compilations. It is important to emphasize that the use of these
options does not change the generated code.

</P>
<P>
The debugging information is written in standard system
formats that are used
by many tools, including debuggers and profilers. The format of the
information is typically designed to describe C types and semantics,
but GNAT implements a translation scheme which allows full details about
Ada types and variables to be encoded into these standard C
formats. Details of this encoding scheme may be found in the file
exp_dbug.ads in the GNAT source distribution. However, the
details of this encoding are, in general, of no interest to a user, since GDB
automatically performs the necessary decoding.

</P>
<P>
When a program is bound and linked, the debugging information is
collected from the object files, and stored in the executable image of
the program. Again, this process significantly increases the size
of the generated executable file,
but it does not increase the size of the
executable program itself. Furthermore, if this program
is run in the normal manner, it runs exactly as if the debug
information were not present, and takes no more actual memory.

</P>
<P>
However, if the program is run under control of GDB, the debugger is activated.
The image of the program is loaded, at which point it is ready to run.
If a run command is
given, then the program will run exactly as it would have if GDB
were not present. This is a crucial part of the GDB design philosophy.
GDB is entirely non-intrusive until a breakpoint is encountered.
If no breakpoint is ever hit, the program will run exactly as it
would if no debugger were present. When a breakpoint is hit,
GDB accesses the debugging information and can respond to user
commands to inspect variables, and more generally to report on the state of
execution.

</P>



<H2><A NAME="SEC150" HREF="gnat_ug_toc.html#TOC150">Running GDB</A></H2>

<P>
The debugger can be launched directly and simply from emacs which allows
to browse and modify directly the source code during the debugging
session, See section <A HREF="gnat_ug.html#SEC142">Ada Mode for <CODE>emacs</CODE></A>. Here is described the basic use of
GDB is text mode.

</P>
<P>
The command to run GDB is

</P>

<PRE>
   $ gdb program
</PRE>

<P>
where <CODE>program</CODE> is the name of the executable file. This
activates the debugger and results in a prompt for debugger commands.
The simplest command is simply <CODE>run</CODE>, which causes the program to run
exactly as if the debugger were not present. The following section
describes some of the additional commands that can be given to GDB.

</P>


<H2><A NAME="SEC151" HREF="gnat_ug_toc.html#TOC151">Introduction to GDB Commands</A></H2>

<P>
GDB contains a large repertoire of commands. The manual
<CITE>Debugging with GDB</CITE>
includes extensive documentation on the use
of these commands, together with examples of their use. Furthermore,
the command <VAR>help</VAR> invoked from within GDB activates a simple help
facility which summarizes the available commands and their options.
In this section we summarize a few of the most commonly
used commands to give an idea of what GDB is about. You should create
a simple program with debugging information and experiment with the use of
these GDB commands on the program as you read through the following section.

</P>
<DL COMPACT>

<DT><CODE>set args <VAR>arguments</VAR></CODE>
<DD>
The <VAR>arguments</VAR> list above is a list of arguments to be passed to
the program on a subsequent run command, just as though the arguments
had been entered on a normal invocation of the program. The <CODE>set args</CODE>
command is not needed if the program does not require arguments.

<DT><CODE>run</CODE>
<DD>
The <CODE>run</CODE> command causes execution of the program to start from the
beginning. If the program is already running, that is to say if you
are currently positioned  at a breakpoint,
then a prompt will ask for confirmation that you want
to abandon the current execution and restart.

<DT><CODE>breakpoint <VAR>location</VAR></CODE>
<DD>
The breakpoint command sets a breakpoint, that is to say a point at which
execution will halt and GDB will await further commands. <VAR>location</VAR> is
either a line number within a file, given in the format <CODE>file:linenumber</CODE>,
or it is the name of a subprogram. If you request that a breakpoint be set on
a subprogram that is overloaded, a prompt will ask you to specify on which of
those subprograms you want to breakpoint. You can also
specify that all of them should be breakpointed. If the program is run
and execution encounters the breakpoint, then the program
stops and GDB signals that the breakpoint was encountered by printing the
line of code before which the program is halted.

<DT><CODE>breakpoint exception <VAR>name</VAR></CODE>
<DD>
A special form of the breakpoint command which breakpoints whenever
exception <VAR>name</VAR> is raised.
If <VAR>name</VAR> is omitted,
then a breakpoint will occur when any exception is raised.

<DT><CODE>print <VAR>expression</VAR></CODE>
<DD>
This will print the value of the given expression. Most simple
Ada expression formats are properly handled by GDB, so the expression
can contain function calls, variables, operators, and attribute references.

<DT><CODE>continue</CODE>
<DD>
Continues execution following a breakpoint, until the next breakpoint or the
termination of the program.

<DT><CODE>step</CODE>
<DD>
Executes a single line after a breakpoint. If the next statement is a subprogram
call, execution continues into (the first statement of) the
called subprogram.

<DT><CODE>next</CODE>
<DD>
Executes a single line. If this line is a subprogram call, executes and
returns from the call.

<DT><CODE>list</CODE>
<DD>
Lists a few lines around the current source location. In practice, it
is usually more convenient to have a separate edit window open with the
relevant source file displayed. Successive applications of this command
print subsequent lines. The command can be given an argument which is a
line number, in which case it displays a few lines around the specified one.

<DT><CODE>backtrace</CODE>
<DD>
Displays a backtrace of the call chain. This command is typically
used after a breakpoint has occurred, to examine the sequence of calls that
leads to the current breakpoint. The display includes one line for each
activation record (frame) corresponding to an active subprogram.

<DT><CODE>up</CODE>
<DD>
At a breakpoint, GDB can display the values of variables local
to the current frame. The command <CODE>up</CODE> can be used to
examine the contents of other active frames, by moving the focus up
the stack, that is to say from callee to caller, one frame at a time.

<DT><CODE>down</CODE>
<DD>
Moves the focus of GDB down from the frame currently being examined to the
frame of its callee (the reverse of the previous command),

<DT><CODE>frame <VAR>n</VAR></CODE>
<DD>
Inspect the frame with the given number. The value 0 denotes the frame
of the current breakpoint, that is to say the top of the call stack.

</DL>

<P>
The above list is a very short introduction to the commands that
GDB provides. Important additional capabilities, including conditional
breakpoints, the ability to execute command sequences on a breakpoint,
the ability to debug at the machine instruction level and many other
features are described in detail in <CITE>Debugging with GDB</CITE>.
Note that most commands can be abbreviated
(for example, c for continue, bt for backtrace).

</P>


<H2><A NAME="SEC152" HREF="gnat_ug_toc.html#TOC152">Using Ada Expressions</A></H2>
<P>
<A NAME="IDX317"></A>

</P>
<P>
GDB supports a fairly large subset of Ada expression syntax, with some
extensions. The philosophy behind the design of this subset is

</P>

<UL>
<LI>

That GDB should provide basic literals and access to operations for
arithmetic, dereferencing, field selection, indexing, and subprogram calls,
leaving more sophisticated computations to subprograms written into the
program (which therefore may be called from GDB).

<LI>

That type safety and strict adherence to Ada language restrictions
are not particularly important to the GDB user.

<LI>

That brevity is important to the GDB user.
</UL>

<P>
Thus, for brevity, the debugger acts as if there were
implicit <CODE>with</CODE> and <CODE>use</CODE> clauses in effect for all user-written
packages, thus making it unnecessary to fully qualify most names with
their packages, regardless of context.  Where this causes ambiguity,
GDB asks the user's intent.

</P>
<P>
For details on the supported Ada syntax <CITE>Debugging with GDB</CITE>.

</P>


<H2><A NAME="SEC153" HREF="gnat_ug_toc.html#TOC153">Calling User-Defined Subprograms</A></H2>

<P>
An important capability of GDB is the ability to call user-defined
subprograms while debugging. This is achieved simply by entering
a subprogram call statement in the form:

</P>

<PRE>
   call subprogram-name (parameters)
</PRE>

<P>
The keyword <CODE>call</CODE> can be omitted in the normal case where the
<CODE>subprogram-name</CODE> does not coincide with any of the predefined
GDB commands.

</P>
<P>
The effect is to invoke the given subprogram, passing it the
list of parameters that is supplied. The parameters can be expressions and
can include variables from the program being debugged. The
subprogram must be defined
at the library level within your program, and GDB will call the
subprogram within the environment of your program execution (which
means that the subprogram is free to access or even modify variables
within your program).

</P>
<P>
The most important use of this facility is in allowing the inclusion of
debugging routines that are tailored to particular data structures
in your program. Such debugging routines can be written to provide a suitably
high-level description of an abstract type, rather than a low-level dump
of its physical layout.  After all, the standard
GDB <CODE>print</CODE> command only knows the physical layout of your
types, not their abstract meaning.  Debugging routines can provide information
at the desired semantic level and are thus enormously useful.

</P>
<P>
For example, when debugging GNAT itself, it is crucial to have access to
the contents of the tree nodes used to represent the program internally.
But tree nodes are represented simply by an integer value (which in turn
is an index into a table of nodes).
Using the <CODE>print</CODE> command on a tree node would simply print this integer
value, which is not very useful. But the PN routine (defined in file
treepr.adb in the GNAT sources) takes a tree node as input, and displays
a useful high level representation of the tree node, which includes the
syntactic category of the node, its position in the source, the integers
that denote descendant nodes and parent node, as well as varied
semantic information. To study this example in more detail, you might want to
look at the body of the PN procedure in the stated file.

</P>


<H2><A NAME="SEC154" HREF="gnat_ug_toc.html#TOC154">Breaking on Ada Exceptions</A></H2>
<P>
<A NAME="IDX318"></A>

</P>
<P>
You can set breakpoints that trip when your program raises
selected exceptions.

</P>
<DL COMPACT>

<DT><CODE>break exception</CODE>
<DD>
Set a breakpoint that trips whenever (any task in the) program raises
any exception.

<DT><CODE>break exception <VAR>name</VAR></CODE>
<DD>
Set a breakpoint that trips whenever (any task in the) program raises
the exception <VAR>name</VAR>.

<DT><CODE>break exception unhandled</CODE>
<DD>
Set a breakpoint that trips whenever (any task in the) program raises an
exception for which there is no handler.

<DT><CODE>info exceptions</CODE>
<DD>
<DT><CODE>info exceptions <VAR>regexp</VAR></CODE>
<DD>
The <CODE>info exceptions</CODE> command permits the user to examine all defined
exceptions within Ada programs.  With a regular expression, <VAR>regexp</VAR>, as
argument, prints out only those exceptions whose name matches <VAR>regexp</VAR>.
</DL>



<H2><A NAME="SEC155" HREF="gnat_ug_toc.html#TOC155">Ada Tasks</A></H2>
<P>
<A NAME="IDX319"></A>

</P>
<P>
GDB allows the following task-related commands:

</P>
<DL COMPACT>

<DT><CODE>info tasks</CODE>
<DD>
This command shows a list of current Ada tasks, as in the following example:


<PRE>
   (gdb) info tasks
     ID       TID P-ID   Thread Pri State                 Name
      1   8088000   0   807e000  15 Child Activation Wait main_task
      2   80a4000   1   80ae000  15 Accept/Select Wait    b
      3   809a800   1   80a4800  15 Child Activation Wait a
   *  4   80ae800   3   80b8000  15 Running               c
</PRE>

In this listing, the asterisk before the first task indicates it to be the
currently running task. The first column lists the task ID that is used
to refer to tasks in the following commands.

<DT><CODE>break <VAR>linespec</VAR> task <VAR>taskid</VAR></CODE>
<DD>
<DT><CODE>break <VAR>linespec</VAR> task <VAR>taskid</VAR> if ...</CODE>
<DD>
<A NAME="IDX320"></A>
These commands are like the <CODE>break ... thread ...</CODE>.
<VAR>linespec</VAR> specifies source lines.

Use the qualifier <SAMP>`task <VAR>taskid</VAR>'</SAMP> with a breakpoint command
to specify that you only want GDB to stop the program when a
particular Ada task reaches this breakpoint.  <VAR>taskid</VAR> is one of the
numeric task identifiers assigned by GDB, shown in the first
column of the <SAMP>`info tasks'</SAMP> display.

If you do not specify <SAMP>`task <VAR>taskid</VAR>'</SAMP> when you set a
breakpoint, the breakpoint applies to <EM>all</EM> tasks of your
program.

You can use the <CODE>task</CODE> qualifier on conditional breakpoints as
well; in this case, place <SAMP>`task <VAR>taskid</VAR>'</SAMP> before the
breakpoint condition (before the <CODE>if</CODE>).

<DT><CODE>task <VAR>taskno</VAR></CODE>
<DD>
<A NAME="IDX321"></A>

This command allows to switch to the task referred by <VAR>taskno</VAR>.  In
particular, This allows to browse the backtrace of the specified
task. It is advised to switch back to the original task before
continuing execution otherwise the scheduling of the program may be
perturbated.
</DL>

<P>
For more detailed information on the tasking support <CITE>Debugging with GDB</CITE>.

</P>



<H2><A NAME="SEC156" HREF="gnat_ug_toc.html#TOC156">Debugging Generic Units</A></H2>
<P>
<A NAME="IDX322"></A>

</P>
<P>
GNAT always uses code expansion for generic instantiation. This means that
each time an instantiation occurs, a complete copy of the original code is
made, with appropriate substitutions of formals by actuals.

</P>
<P>
It is not possible to refer to the original generic entities in GDB, but it
is always possible to debug a particular instance of a generic, by using
the appropriate expanded names. For example, if we have

</P>

<PRE>
   <B>procedure</B> g <B>is</B>

      <B>generic package</B> k <B>is</B>
         <B>procedure</B> kp (v1 : <B>in out</B> integer);
      <B>end</B> k;

      <B>package body</B> k <B>is</B>
         <B>procedure</B> kp (v1 : <B>in out</B> integer) <B>is</B>
         <B>begin</B>
            v1 := v1 + 1;
         <B>end</B> kp;
      <B>end</B> k;

      <B>package</B> k1 <B>is new</B> k;
      <B>package</B> k2 <B>is new</B> k;

      var : integer := 1;

   <B>begin</B>
      k1.kp (var);
      k2.kp (var);
      k1.kp (var);
      k2.kp (var);
   <B>end</B>;
</PRE>

<P>
Then to break on a call to procedure kp in the k2 instance, simply
use the command:

</P>

<PRE>
   (gdb) break g.k2.kp
</PRE>

<P>
When the breakpoint occurs, you can step through the code of the
instance in the normal manner and examine the values of local variables, as for
other units.

</P>



<H2><A NAME="SEC157" HREF="gnat_ug_toc.html#TOC157">GNAT Abnormal Termination</A></H2>
<P>
<A NAME="IDX323"></A>

</P>
<P>
When presented with programs that contain serious errors in syntax
or semantics,
GNAT may on rare occasions  experience problems in operation, such
as aborting with a
segmentation fault or illegal memory access, raising an internal
exception, or terminating abnormally. In such cases, you can activate
various features of GNAT that can help you pinpoint the construct in your
program that is the likely source of the problem.

</P>
<P>
The following strategies are presented in increasing order of
difficulty, corresponding to your programming skills and your
familiarity with compiler internals.

</P>

<OL>
<LI>

Run <CODE>gcc</CODE> with the <CODE>-gnatf</CODE> and <CODE>-gnate</CODE> switches. The first
switch causes all errors on a given line to be reported. In its absence,
only the first error on a line is displayed.

The <CODE>-gnate</CODE> switch causes errors to be displayed as soon as they
are encountered, rather than after compilation is terminated. If GNAT
terminates prematurely, the last error message displayed is likely to
pinpoint the culprit.

<LI>

Run <CODE>gcc</CODE> with the <CODE>-v (verbose)</CODE> switch. In this mode,
<CODE>gcc</CODE> produces ongoing information about the progress of the
compilation and provides the name of each procedure as code is
generated. This switch allows you to find which Ada procedure was being
compiled when it encountered a code generation problem.

<LI>

<A NAME="IDX324"></A>
Run <CODE>gcc</CODE> with the <CODE>-gnatdc</CODE> switch. This is a GNAT specific
switch that does for the front-end what <CODE>-v</CODE> does for the back end.
The system prints the name of each unit, either a compilation unit or
nested unit, as it is being analyzed.
<LI>

Finally, you can start
<CODE>gdb</CODE> directly on the <CODE>gnat1</CODE> executable. <CODE>gnat1</CODE> is the
front-end of GNAT, and can be run independently (normally it is just
called from <CODE>gcc</CODE>). You can use <CODE>gdb</CODE> on <CODE>gnat1</CODE> as you
would on a C program (but see section <A HREF="gnat_ug.html#SEC149">The GNAT Debugger GDB</A> for caveats).  The
<CODE>where</CODE> command is the first line of attack; the variable
<CODE>lineno</CODE> (seen by <CODE>print lineno</CODE>), used by the second phase of
<CODE>gnat1</CODE> and by the <CODE>gcc</CODE> backend, indicates the source line at
which the execution stopped, and <CODE>input_file name</CODE> indicates the name of
the source file.
</OL>



<H2><A NAME="SEC158" HREF="gnat_ug_toc.html#TOC158">Naming Conventions for GNAT Source Files</A></H2>

<P>
In order to examine the workings of the GNAT system, the following
brief description of its organization may be helpful:

</P>

<UL>
<LI>

Files with prefix <TT>`sc'</TT> contain the lexical scanner.

<LI>

All files prefixed with <TT>`par'</TT> are components of the parser. The
numbers correspond to chapters of the Ada 95 Reference Manual. For example,
parsing of select statements can be found in <TT>`par-ch9.adb'</TT>.

<LI>

All files prefixed with <TT>`sem'</TT> perform semantic analysis. The
numbers correspond to chapters of the Ada standard. For example, all
issues involving context clauses can be found in <TT>`sem_ch10.adb'</TT>. In
addition, some features of the language require sufficient special processing
to justify their own semantic files: sem_aggr for aggregates, sem_disp for
dynamic dispatching, etc.

<LI>

All files prefixed with <TT>`exp'</TT> perform normalization and
expansion of the intermediate representation (abstract syntax tree, or AST).
these files use the same numbering scheme as the parser and semantics files.
For example, the construction of record initialization procedures is done in
<TT>`exp_ch3.adb'</TT>.

<LI>

The files prefixed with <TT>`bind'</TT> implement the binder, which
verifies the consistency of the compilation, determines an order of
elaboration, and generates the bind file.

<LI>

The files <TT>`atree.ads'</TT> and <TT>`atree.adb'</TT> detail the low-level
data structures used by the front-end.

<LI>

The files <TT>`sinfo.ads'</TT> and <TT>`sinfo.adb'</TT> detail the structure of
the abstract syntax tree as produced by the parser.

<LI>

The files <TT>`einfo.ads'</TT> and <TT>`einfo.adb'</TT> detail the attributes of
all entities, computed during semantic analysis.

<LI>

Library management issues are dealt with in files with prefix
<TT>`lib'</TT>.

<LI>

<A NAME="IDX325"></A>
<A NAME="IDX326"></A>
Ada files with the prefix <TT>`a-'</TT> are children of <CODE>Ada</CODE>, as
defined in Annex A.

<LI>

<A NAME="IDX327"></A>
<A NAME="IDX328"></A>
Files with prefix <TT>`i-'</TT> are children of <CODE>Interfaces</CODE>, as
defined in Annex B.

<LI>

<A NAME="IDX329"></A>
Files with prefix <TT>`s-'</TT> are children of <CODE>System</CODE>. This includes
both language-defined children and GNAT run-time routines.

<LI>

<A NAME="IDX330"></A>
Files with prefix <TT>`g-'</TT> are children of <CODE>GNAT</CODE>. These are useful
general-purpose packages, fully documented in their specifications. All
the other <TT>`.c'</TT> files are modifications of common <CODE>gcc</CODE> files.
</UL>



<H2><A NAME="SEC159" HREF="gnat_ug_toc.html#TOC159">Getting Internal Debugging Information</A></H2>

<P>
Most compilers have internal debugging switches and modes. GNAT
does also, except GNAT internal debugging switches and modes are not
secret. A summary and full description of all the compiler and binder
debug flags are in the file <TT>`debug.adb'</TT>. You must obtain the
sources of the compiler to see the full detailed effects of these flags.

</P>
<P>
The switches that print the source of the program (reconstructed from
the internal tree) are of general interest for user programs, as are the
options to print
the full internal tree, and the entity table (the symbol table
information).  The reconstructed source provides a readable version of the
program after the front-end has completed analysis and  expansion, and is useful
when studying the performance of specific constructs. For example, constraint
checks are indicated, complex aggregates are replaced with loops and
assignments, and tasking primitives are replaced with run-time calls.

</P>



<H1><A NAME="SEC160" HREF="gnat_ug_toc.html#TOC160">Performance Considerations</A></H1>
<P>
<A NAME="IDX331"></A>

</P>
<P>
The GNAT system provides a number of options that allow a trade-off
between

</P>

<UL>
<LI>

performance of the generated code

<LI>

speed of compilation

<LI>

minimization of dependences and recompilation

<LI>

the degree of run-time checking.
</UL>

<P>
The defaults (if no options are selected) aim at improving the speed
of compilation and minimizing dependences, at the expense of performance
of the generated code:

</P>

<UL>
<LI>

no optimization

<LI>

no inlining of subprogram calls

<LI>

all run-time checks enabled except overflow and elaboration checks
</UL>

<P>
These options are suitable for most program development purposes. This
chapter describes how you can modify these choices.

</P>

<UL>
<LI><A HREF="gnat_ug.html#SEC161">Controlling Run-time Checks</A>
<LI><A HREF="gnat_ug.html#SEC162">Optimization Levels</A>
<LI><A HREF="gnat_ug.html#SEC163">Inlining of Subprograms</A>
</UL>



<H2><A NAME="SEC161" HREF="gnat_ug_toc.html#TOC161">Controlling Run-time Checks</A></H2>

<P>
By default, GNAT produces all run-time checks, except arithmetic overflow
checking for integer operations (that includes division by zero) and checks
for access before elaboration on subprogram calls.
<A NAME="IDX332"></A>
<A NAME="IDX333"></A>
Two gnat switches, <CODE>-gnatp</CODE> and <CODE>-gnato</CODE> allow this default to
be modified.  See section <A HREF="gnat_ug.html#SEC39">Run-time Checks</A>.

</P>
<P>
Our experience is that the default is suitable for most development
purposes.

</P>
<P>
We treat integer overflow specially because these
are quite expensive and in our experience are not as important as other
run-time checks in the development process.

</P>
<P>
Elaboration checks are off by default, and also not needed by default, since
GNAT uses a static elaboration analysis approach that avoids the need for
run-time checking. This manual contains a full chapter discussing the issue
of elaboration checks, and if the default is not satisfactory for your use,
you should read this chapter.

</P>
<P>
<A NAME="IDX334"></A>
<A NAME="IDX335"></A>
<A NAME="IDX336"></A>
<A NAME="IDX337"></A>
<A NAME="IDX338"></A>
Note that the setting of the switches controls the default setting of
the checks. They may be modified using either <CODE>pragma Suppress</CODE> (to
remove checks) or <CODE>pragma Unsuppress</CODE> (to add back suppressed
checks) in the program source.

</P>


<H2><A NAME="SEC162" HREF="gnat_ug_toc.html#TOC162">Optimization Levels</A></H2>
<P>
<A NAME="IDX339"></A>

</P>
<P>
The default is optimization off. This results in the fastest compile
times, but GNAT makes absolutely no attempt to optimize, and the
generated programs are considerably larger and slower than when
optimization is enabled. You can use the
<CODE>-O<VAR>n</VAR></CODE> switch, where <VAR>n</VAR> is an integer from 0 to 3,
on the <CODE>gcc</CODE> command line to control the optimization level:

</P>
<DL COMPACT>

<DT><CODE>-O0</CODE>
<DD>
no optimization (the default)

<DT><CODE>-O1</CODE>
<DD>
medium level optimization

<DT><CODE>-O2</CODE>
<DD>
full optimization

<DT><CODE>-O3</CODE>
<DD>
full optimization, and also attempt automatic inlining of small
subprograms within a unit (see section <A HREF="gnat_ug.html#SEC163">Inlining of Subprograms</A>).
</DL>

<P>
Higher optimization levels perform more global transformations on the
program and apply more expensive analysis algorithms in order to generate
faster and more compact code.  The price in compilation time, and the
resulting improvement in execution time,
both depend on the particular application and the hardware environment.
You should experiment to find the best level for your application.

</P>
<P>
Note: Unlike some other compilation systems, <CODE>gcc</CODE> has
been tested extensively at all optimization levels. There are some bugs
which appear only with optimization turned on, but there have also been
bugs which show up only in <EM>unoptimized</EM> code. Selecting a lower
level of optimization does not improve the reliability of the code
generator, which in practice is highly reliable at all optimization
levels.

</P>


<H2><A NAME="SEC163" HREF="gnat_ug_toc.html#TOC163">Inlining of Subprograms</A></H2>

<P>
A call to a subprogram in the current unit is inlined if all the
following conditions are met:

</P>

<UL>
<LI>

The optimization level is at least <CODE>-O1</CODE>.

<LI>

The called subprogram is suitable for inlining: It must be small enough
and not contain nested subprograms or anything else that <CODE>gcc</CODE>
cannot support in inlined subprograms.

<LI>

The call occurs after the definition of the body of the subprogram.

<LI>

<A NAME="IDX340"></A>
Either <CODE>pragma Inline</CODE> applies to the subprogram or it is
small and automatic inlining (optimization level <CODE>-O3</CODE>) is
specified.
</UL>

<P>
Calls to subprograms in <CODE>with</CODE>'ed units are normally not inlined.
To achieve this level of inlining, the following conditions must all be
true:

</P>

<UL>
<LI>

The optimization level is at least <CODE>-O1</CODE>.

<LI>

The called subprogram is suitable for inlining: It must be small enough
and not contain nested subprograms or anything else <CODE>gcc</CODE> cannot
support in inlined subprograms.

<LI>

The call appears in a body (not in a package spec).

<LI>

There is a <CODE>pragma Inline</CODE> for the subprogram.

<LI>

<A NAME="IDX341"></A>
The <CODE>-gnatn</CODE> switch
is used in the <CODE>gcc</CODE> command line
</UL>

<P>
Note that specifying the <CODE>-gnatn</CODE> switch causes additional
compilation dependencies.  Consider the following:

</P>

<PRE>
   <B>package</B> R <B>is</B>
      <B>procedure</B> Q;
      <B>pragma</B> Inline (Q);
   <B>end</B> R;
   <B>package body</B> R <B>is</B>
      ...
   <B>end</B> R;

   <B>with</B> R;
   <B>procedure</B> Main <B>is</B>
   <B>begin</B>
      ...
      R.Q;
   <B>end</B> Main;
</PRE>

<P>
With the default behavior (no <CODE>-gnatn</CODE> switch specified), the
compilation of the <CODE>Main</CODE> procedure depends only on its own source,
<TT>`main.adb'</TT>, and the spec of the package in file <TT>`r.ads'</TT>. This
means that editing the body of <CODE>R</CODE> does not require recompiling
<CODE>Main</CODE>.

</P>
<P>
On the other hand, the call <CODE>R.Q</CODE> is not inlined under these
circumstances. If the <CODE>-gnatn</CODE> switch is present when <CODE>Main</CODE>
is compiled, the call will be inlined if the body of <CODE>Q</CODE> is small
enough, but now <CODE>Main</CODE> depends on the body of <CODE>R</CODE> in
<TT>`r.adb'</TT> as well as on the spec. This means that if this body is edited,
the main program must be recompiled.  Note that this extra dependency
occurs whether or not the call is in fact inlined by <CODE>gcc</CODE>.

</P>
<P>
<A NAME="IDX342"></A>
Note: The <CODE>-fno-inline</CODE> switch
can be used to prevent
all inlining. This switch overrides all other conditions and ensures
that no inlining occurs. The extra dependences resulting from
<CODE>-gnatn</CODE> will still be active, even if
this switch is used to suppress the resulting inlining actions.

</P>



<H1><A NAME="SEC164" HREF="gnat_ug_toc.html#TOC164">Index</A></H1>

<P>
<H2>-</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX213"><CODE>--GCC=compiler_name</CODE> (<CODE>gnatlink</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX217"><CODE>--GCC=compiler_name</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX218"><CODE>--GNATBIND=binder_name</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX219"><CODE>--GNATLINK=linker_name</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX214"><CODE>--LINK=</CODE> (<CODE>gnatlink</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX307"><CODE>-83</CODE> (<CODE>gnathtml</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX182"><CODE>-A</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX203"><CODE>-A</CODE> (<CODE>gnatlink</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX285"><CODE>-a</CODE> (<CODE>gnatls</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX239"><CODE>-A</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX220"><CODE>-a</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX235"><CODE>-aI</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX236"><CODE>-aL</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX237"><CODE>-aO</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX79"><CODE>-B</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX78"><CODE>-b</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX172"><CODE>-b</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX212"><CODE>-B</CODE> (<CODE>gnatlink</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX211"><CODE>-b</CODE> (<CODE>gnatlink</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX248"><CODE>-bargs</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX80"><CODE>-c</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX183"><CODE>-C</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX189"><CODE>-c</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX254"><CODE>-c</CODE> (<CODE>gnatchop</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX204"><CODE>-C</CODE> (<CODE>gnatlink</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX221"><CODE>-c</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX247"><CODE>-cargs</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX308"><CODE>-d</CODE> (<CODE>gnathtml</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX286"><CODE>-d</CODE> (<CODE>gnatls</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX184"><CODE>-e</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX180"><CODE>-f</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX309"><CODE>-f</CODE> (<CODE>gnathtml</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX222"><CODE>-f</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX342"><CODE>-fno-inline</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX81"><CODE>-g</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX206"><CODE>-g</CODE> (<CODE>gnatlink</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX136"><CODE>-gnat83</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX139"><CODE>-gnat95</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX111"><CODE>-gnata</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX98"><CODE>-gnatb</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX134"><CODE>-gnatc</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX154"><CODE>-gnatD</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX324"><CODE>-gnatdc</CODE> switch</A>
<LI><A HREF="gnat_ug.html#IDX128"><CODE>-gnatE</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX103"><CODE>-gnate</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX100"><CODE>-gnatf</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX153"><CODE>-gnatG</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX141"><CODE>-gnatg</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX144"><CODE>-gnati</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX146"><CODE>-gnatk</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX96"><CODE>-gnatl</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX99"><CODE>-gnatm</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX31"><CODE>-gnatn</CODE> switch</A>
<LI><A HREF="gnat_ug.html#IDX147"><CODE>-gnatn</CODE> (<CODE>gcc</CODE>)</A>, <A HREF="gnat_ug.html#IDX341"><CODE>-gnatn</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX124"><CODE>-gnato</CODE> (<CODE>gcc</CODE>)</A>, <A HREF="gnat_ug.html#IDX333"><CODE>-gnato</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX120"><CODE>-gnatp</CODE> (<CODE>gcc</CODE>)</A>, <A HREF="gnat_ug.html#IDX332"><CODE>-gnatp</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX102"><CODE>-gnatq</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX109"><CODE>-gnatR</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX140"><CODE>-gnatr</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX132"><CODE>-gnats</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX148"><CODE>-gnatt</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX97"><CODE>-gnatU</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX151"><CODE>-gnatu</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX94"><CODE>-gnatv</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX145"><CODE>-gnatW</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX105"><CODE>-gnatwe</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX107"><CODE>-gnatwl</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX106"><CODE>-gnatws</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX108"><CODE>-gnatwu</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX110"><CODE>-gnatx</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX181"><CODE>-h</CODE> (<CODE>gnatbind</CODE>)</A>, <A HREF="gnat_ug.html#IDX185"><CODE>-h</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX287"><CODE>-h</CODE> (<CODE>gnatls</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX84"><CODE>-I-</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX241"><CODE>-I-</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX82"><CODE>-I</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX311"><CODE>-I</CODE> (<CODE>gnathtml</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX240"><CODE>-I</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX223"><CODE>-i</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX297"><CODE>-i</CODE> (<CODE>gnatmem</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX224"><CODE>-j</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX255"><CODE>-k</CODE> (<CODE>gnatchop</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX226"><CODE>-k</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX186"><CODE>-l</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX310"><CODE>-l</CODE> (<CODE>gnathtml</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX243"><CODE>-L</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX249"><CODE>-largs</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX174"><CODE>-M</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX173"><CODE>-m</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX229"><CODE>-M</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX227"><CODE>-m</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX190"><CODE>-n</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX207"><CODE>-n</CODE> (<CODE>gnatlink</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX230"><CODE>-n</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX245"><CODE>-nostdinc</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX246"><CODE>-nostdlib</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX87"><CODE>-O</CODE> (<CODE>gcc</CODE>)</A>, <A HREF="gnat_ug.html#IDX339"><CODE>-O</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX86"><CODE>-o</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX188"><CODE>-o</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX187"><CODE>-O</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX312"><CODE>-o</CODE> (<CODE>gnathtml</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX210"><CODE>-o</CODE> (<CODE>gnatlink</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX288"><CODE>-o</CODE> (<CODE>gnatls</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX231"><CODE>-o</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX296"><CODE>-o</CODE> (<CODE>gnatmem</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX313"><CODE>-p</CODE> (<CODE>gnathtml</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX256"><CODE>-q</CODE> (<CODE>gnatchop</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX232"><CODE>-q</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX294"><CODE>-q</CODE> (<CODE>gnatmem</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX257"><CODE>-r</CODE> (<CODE>gnatchop</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX88"><CODE>-S</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX169"><CODE>-s</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX289"><CODE>-s</CODE> (<CODE>gnatls</CODE>)</A>, <A HREF="gnat_ug.html#IDX291"><CODE>-s</CODE> (<CODE>gnatls</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX178"><CODE>-t</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX290"><CODE>-u</CODE> (<CODE>gnatls</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX209"><CODE>-v -v</CODE> (<CODE>gnatlink</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX90"><CODE>-V</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX89"><CODE>-v</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX171"><CODE>-v</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX259"><CODE>-v</CODE> (<CODE>gnatchop</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX208"><CODE>-v</CODE> (<CODE>gnatlink</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX233"><CODE>-v</CODE> (<CODE>gnatmake</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX260"><CODE>-w</CODE> (<CODE>gnatchop</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX177"><CODE>-we</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX175"><CODE>-ws</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX91"><CODE>-Wuninitialized</CODE> (<CODE>gcc</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX170"><CODE>-x</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX194"><CODE>-z</CODE> (<CODE>gnatbind</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX234"><CODE>-z</CODE> (<CODE>gnatmake</CODE>)</A>
</DIR>
<H2>_</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX165">__gnat_finalize</A>
<LI><A HREF="gnat_ug.html#IDX164">__gnat_initialize</A>
<LI><A HREF="gnat_ug.html#IDX306">_main</A>
</DIR>
<H2>a</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX117">Access before elaboration</A>
<LI><A HREF="gnat_ug.html#IDX277">Access-to-subprogram</A>
<LI><A HREF="gnat_ug.html#IDX137">ACVC, Ada 83 tests</A>
<LI><A HREF="gnat_ug.html#IDX198">Ada</A>, <A HREF="gnat_ug.html#IDX325">Ada</A>
<LI><A HREF="gnat_ug.html#IDX135">Ada 83 compatibility</A>
<LI><A HREF="gnat_ug.html#IDX1">Ada 95 Language Reference Manual</A>
<LI><A HREF="gnat_ug.html#IDX317">Ada expressions</A>
<LI><A HREF="gnat_ug.html#IDX16">Ada.Characters.Latin_1</A>
<LI><A HREF="gnat_ug.html#IDX161">Ada.Command_Line</A>
<LI><A HREF="gnat_ug.html#IDX163">Ada.Command_Line.Set_Exit_Status</A>
<LI><A HREF="gnat_ug.html#IDX155">ADA_INCLUDE_PATH</A>
<LI><A HREF="gnat_ug.html#IDX197">ADA_OBJECTS_PATH</A>
<LI><A HREF="gnat_ug.html#IDX192">adafinal</A>
<LI><A HREF="gnat_ug.html#IDX191">adainit</A>
<LI><A HREF="gnat_ug.html#IDX326">Annex A</A>
<LI><A HREF="gnat_ug.html#IDX328">Annex B</A>
<LI><A HREF="gnat_ug.html#IDX159">argc</A>
<LI><A HREF="gnat_ug.html#IDX160">argv</A>
<LI><A HREF="gnat_ug.html#IDX298">ASIS</A>
<LI><A HREF="gnat_ug.html#IDX299">ASIS-for-GNAT</A>
<LI><A HREF="gnat_ug.html#IDX112">Assert</A>
<LI><A HREF="gnat_ug.html#IDX114">Assertions</A>
</DIR>
<H2>b</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX48">Binder output file</A>
<LI><A HREF="gnat_ug.html#IDX193">Binder, multiple input files</A>
<LI><A HREF="gnat_ug.html#IDX168">Body_Version</A>
<LI><A HREF="gnat_ug.html#IDX320">breakpoints and tasks</A>
</DIR>
<H2>c</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX60">C</A>
<LI><A HREF="gnat_ug.html#IDX63">C++</A>
<LI><A HREF="gnat_ug.html#IDX50">Calling Conventions</A>
<LI><A HREF="gnat_ug.html#IDX130">Check, elaboration</A>
<LI><A HREF="gnat_ug.html#IDX126">Check, overflow</A>
<LI><A HREF="gnat_ug.html#IDX119">Checks, access before elaboration</A>
<LI><A HREF="gnat_ug.html#IDX118">Checks, division by zero</A>
<LI><A HREF="gnat_ug.html#IDX122">Checks, suppressing</A>
<LI><A HREF="gnat_ug.html#IDX57">COBOL</A>
<LI><A HREF="gnat_ug.html#IDX20">code page 437</A>
<LI><A HREF="gnat_ug.html#IDX21">code page 850</A>
<LI><A HREF="gnat_ug.html#IDX92">Combining GNAT switches</A>
<LI><A HREF="gnat_ug.html#IDX5">Compilation model</A>
<LI><A HREF="gnat_ug.html#IDX261">Configuration pragmas</A>
<LI><A HREF="gnat_ug.html#IDX53">Convention, Ada</A>
<LI><A HREF="gnat_ug.html#IDX55">Convention, Asm</A>
<LI><A HREF="gnat_ug.html#IDX56">Convention, Assembler</A>
<LI><A HREF="gnat_ug.html#IDX62">Convention, C</A>
<LI><A HREF="gnat_ug.html#IDX65">Convention, C++</A>
<LI><A HREF="gnat_ug.html#IDX59">Convention, COBOL</A>
<LI><A HREF="gnat_ug.html#IDX68">Convention, Fortran</A>
<LI><A HREF="gnat_ug.html#IDX70">Convention, Stdcall</A>
<LI><A HREF="gnat_ug.html#IDX72">Convention, Stubbed</A>
<LI><A HREF="gnat_ug.html#IDX2">Conventions</A>
<LI><A HREF="gnat_ug.html#IDX9">CR</A>
</DIR>
<H2>d</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX113">Debug</A>
<LI><A HREF="gnat_ug.html#IDX315">debugger</A>
<LI><A HREF="gnat_ug.html#IDX314">debugging</A>
<LI><A HREF="gnat_ug.html#IDX205">Debugging information, including</A>
<LI><A HREF="gnat_ug.html#IDX152">Debugging options</A>
<LI><A HREF="gnat_ug.html#IDX228">Dependencies, producing list</A>
<LI><A HREF="gnat_ug.html#IDX216">Dependency rules</A>
<LI><A HREF="gnat_ug.html#IDX116">Division by zero</A>
</DIR>
<H2>e</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX273">Elaborate</A>
<LI><A HREF="gnat_ug.html#IDX275">Elaborate_All</A>
<LI><A HREF="gnat_ug.html#IDX271">Elaborate_Body</A>
<LI><A HREF="gnat_ug.html#IDX129">Elaboration checks</A>, <A HREF="gnat_ug.html#IDX266">Elaboration checks</A>
<LI><A HREF="gnat_ug.html#IDX265">Elaboration control</A>, <A HREF="gnat_ug.html#IDX278">Elaboration control</A>
<LI><A HREF="gnat_ug.html#IDX73">Elaboration order control</A>
<LI><A HREF="gnat_ug.html#IDX304">Eliminate</A>
<LI><A HREF="gnat_ug.html#IDX12">End of source file</A>
<LI><A HREF="gnat_ug.html#IDX101">Error messages, suppressing</A>
<LI><A HREF="gnat_ug.html#IDX24">EUC Coding</A>
<LI><A HREF="gnat_ug.html#IDX318">exceptions</A>
<LI><A HREF="gnat_ug.html#IDX305">Export</A>
</DIR>
<H2>f</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX11">FF</A>
<LI><A HREF="gnat_ug.html#IDX25">File names</A>
<LI><A HREF="gnat_ug.html#IDX49">Foreign Languages</A>
<LI><A HREF="gnat_ug.html#IDX66">Fortran</A>
</DIR>
<H2>g</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX316">GDB</A>
<LI><A HREF="gnat_ug.html#IDX138">Generic formal parameters</A>
<LI><A HREF="gnat_ug.html#IDX29">Generics</A>, <A HREF="gnat_ug.html#IDX322">Generics</A>
<LI><A HREF="gnat_ug.html#IDX201">GNAT</A>, <A HREF="gnat_ug.html#IDX330">GNAT</A>
<LI><A HREF="gnat_ug.html#IDX323">GNAT Abnormal Termination</A>
<LI><A HREF="gnat_ug.html#IDX4">GNAT compilation model</A>
<LI><A HREF="gnat_ug.html#IDX74">GNAT library</A>
<LI><A HREF="gnat_ug.html#IDX27"><TT>`gnat.adc'</TT></A>, <A HREF="gnat_ug.html#IDX263"><TT>`gnat.adc'</TT></A>
<LI><A HREF="gnat_ug.html#IDX77">gnat1</A>
<LI><A HREF="gnat_ug.html#IDX196">gnat_argc</A>
<LI><A HREF="gnat_ug.html#IDX195">gnat_argv</A>
<LI><A HREF="gnat_ug.html#IDX162">gnat_exit_status</A>
<LI><A HREF="gnat_ug.html#IDX157">gnatbind</A>
<LI><A HREF="gnat_ug.html#IDX253">gnatchop</A>
<LI><A HREF="gnat_ug.html#IDX303">gnatelim</A>
<LI><A HREF="gnat_ug.html#IDX280">gnatfind</A>
<LI><A HREF="gnat_ug.html#IDX281">gnatkr</A>
<LI><A HREF="gnat_ug.html#IDX202">gnatlink</A>
<LI><A HREF="gnat_ug.html#IDX283">gnatls</A>
<LI><A HREF="gnat_ug.html#IDX215">gnatmake</A>
<LI><A HREF="gnat_ug.html#IDX293">gnatmem</A>
<LI><A HREF="gnat_ug.html#IDX282">gnatprep</A>
<LI><A HREF="gnat_ug.html#IDX302">gnatstub</A>
<LI><A HREF="gnat_ug.html#IDX34">Gnatvsn</A>
<LI><A HREF="gnat_ug.html#IDX279">gnatxref</A>
<LI><A HREF="gnat_ug.html#IDX252">gnu make</A>
</DIR>
<H2>h</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX8">HT</A>
</DIR>
<H2>i</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX30">Inline</A>
<LI><A HREF="gnat_ug.html#IDX75">Inlining</A>
<LI><A HREF="gnat_ug.html#IDX200">Interfaces</A>, <A HREF="gnat_ug.html#IDX327">Interfaces</A>
<LI><A HREF="gnat_ug.html#IDX51">Interfacing to Ada</A>
<LI><A HREF="gnat_ug.html#IDX54">Interfacing to Assembler</A>
<LI><A HREF="gnat_ug.html#IDX61">Interfacing to C</A>
<LI><A HREF="gnat_ug.html#IDX64">Interfacing to C++</A>
<LI><A HREF="gnat_ug.html#IDX58">Interfacing to COBOL</A>
<LI><A HREF="gnat_ug.html#IDX67">Interfacing to Fortran</A>
<LI><A HREF="gnat_ug.html#IDX150">Internal trees, writing to file</A>
</DIR>
<H2>l</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX6">Latin-1</A>, <A HREF="gnat_ug.html#IDX15">Latin-1</A>
<LI><A HREF="gnat_ug.html#IDX17">Latin-2</A>
<LI><A HREF="gnat_ug.html#IDX18">Latin-3</A>
<LI><A HREF="gnat_ug.html#IDX19">Latin-4</A>
<LI><A HREF="gnat_ug.html#IDX10">LF</A>
<LI><A HREF="gnat_ug.html#IDX292">library</A>
<LI><A HREF="gnat_ug.html#IDX284">library browser</A>
<LI><A HREF="gnat_ug.html#IDX244">Linker libraries</A>
<LI><A HREF="gnat_ug.html#IDX46">Linker_Option</A>
</DIR>
<H2>m</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX127">Machine_Overflows</A>
<LI><A HREF="gnat_ug.html#IDX251">makefile</A>
<LI><A HREF="gnat_ug.html#IDX47">Mixed Language Programming</A>
<LI><A HREF="gnat_ug.html#IDX133">Multiple units, syntax checking</A>
</DIR>
<H2>n</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX295"><CODE>n</CODE> (<CODE>gnatmem</CODE>)</A>
<LI><A HREF="gnat_ug.html#IDX76">No code generated</A>
</DIR>
<H2>o</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX264">Order of elaboration</A>
<LI><A HREF="gnat_ug.html#IDX52">Other Ada compilers</A>
<LI><A HREF="gnat_ug.html#IDX125">Overflow checks</A>, <A HREF="gnat_ug.html#IDX334">Overflow checks</A>
</DIR>
<H2>p</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX225">Parallel make</A>
<LI><A HREF="gnat_ug.html#IDX331">performance</A>
<LI><A HREF="gnat_ug.html#IDX43">pragma Elaborate</A>, <A HREF="gnat_ug.html#IDX274">pragma Elaborate</A>
<LI><A HREF="gnat_ug.html#IDX44">pragma Elaborate_All</A>, <A HREF="gnat_ug.html#IDX276">pragma Elaborate_All</A>
<LI><A HREF="gnat_ug.html#IDX37">pragma Elaborate_Body</A>, <A HREF="gnat_ug.html#IDX272">pragma Elaborate_Body</A>
<LI><A HREF="gnat_ug.html#IDX340">pragma Inline</A>
<LI><A HREF="gnat_ug.html#IDX39">pragma Preelaborate</A>, <A HREF="gnat_ug.html#IDX270">pragma Preelaborate</A>
<LI><A HREF="gnat_ug.html#IDX38">pragma Pure</A>, <A HREF="gnat_ug.html#IDX267">pragma Pure</A>
<LI><A HREF="gnat_ug.html#IDX40">pragma Remote_Call_Interface</A>
<LI><A HREF="gnat_ug.html#IDX41">pragma Remote_Types</A>
<LI><A HREF="gnat_ug.html#IDX42">pragma Shared_Passive</A>
<LI><A HREF="gnat_ug.html#IDX337">pragma Suppress</A>
<LI><A HREF="gnat_ug.html#IDX338">pragma Unsuppress</A>
<LI><A HREF="gnat_ug.html#IDX262">Pragmas, configuration</A>
<LI><A HREF="gnat_ug.html#IDX269">Preelaborate</A>
<LI><A HREF="gnat_ug.html#IDX35">Priority</A>
<LI><A HREF="gnat_ug.html#IDX268">Pure</A>
</DIR>
<H2>r</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX250">Recompilation, by <CODE>gnatmake</CODE></A>
<LI><A HREF="gnat_ug.html#IDX83">RTL</A>, <A HREF="gnat_ug.html#IDX85">RTL</A>
</DIR>
<H2>s</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX238">Search paths, for <CODE>gnatmake</CODE></A>
<LI><A HREF="gnat_ug.html#IDX23">Shift JIS Coding</A>
<LI><A HREF="gnat_ug.html#IDX13">Source file, end</A>
<LI><A HREF="gnat_ug.html#IDX242">Source files, suppressing search</A>
<LI><A HREF="gnat_ug.html#IDX158">Source files, use by binder</A>
<LI><A HREF="gnat_ug.html#IDX26">Source_File_Name pragma</A>
<LI><A HREF="gnat_ug.html#IDX258">Source_Reference</A>
<LI><A HREF="gnat_ug.html#IDX32">Standard</A>, <A HREF="gnat_ug.html#IDX33">Standard</A>, <A HREF="gnat_ug.html#IDX143">Standard</A>
<LI><A HREF="gnat_ug.html#IDX69">Stdcall</A>
<LI><A HREF="gnat_ug.html#IDX93">stderr</A>
<LI><A HREF="gnat_ug.html#IDX95">stdout</A>
<LI><A HREF="gnat_ug.html#IDX45">Stringt</A>
<LI><A HREF="gnat_ug.html#IDX71">Stubbed</A>
<LI><A HREF="gnat_ug.html#IDX142">Style</A>
<LI><A HREF="gnat_ug.html#IDX115">Style checking</A>
<LI><A HREF="gnat_ug.html#IDX14">SUB</A>
<LI><A HREF="gnat_ug.html#IDX28">Subunits</A>
<LI><A HREF="gnat_ug.html#IDX123">Suppress</A>, <A HREF="gnat_ug.html#IDX335">Suppress</A>
<LI><A HREF="gnat_ug.html#IDX121">Suppressing checks</A>
<LI><A HREF="gnat_ug.html#IDX199">System</A>, <A HREF="gnat_ug.html#IDX329">System</A>
<LI><A HREF="gnat_ug.html#IDX156">System.IO</A>
<LI><A HREF="gnat_ug.html#IDX166">System.Task_Specific_Data</A>
</DIR>
<H2>t</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX321">task switching</A>
<LI><A HREF="gnat_ug.html#IDX319">tasks</A>
<LI><A HREF="gnat_ug.html#IDX179">Time stamp errors, in binder</A>
<LI><A HREF="gnat_ug.html#IDX300">tree file</A>
<LI><A HREF="gnat_ug.html#IDX301">tree output file</A>
<LI><A HREF="gnat_ug.html#IDX3">Typographical conventions</A>
</DIR>
<H2>u</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX36">Uname</A>
<LI><A HREF="gnat_ug.html#IDX131">Unsuppress</A>, <A HREF="gnat_ug.html#IDX336">Unsuppress</A>
<LI><A HREF="gnat_ug.html#IDX22">Upper-Half Coding</A>
</DIR>
<H2>v</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX167">Version</A>
<LI><A HREF="gnat_ug.html#IDX7">VT</A>
</DIR>
<H2>w</H2>
<DIR>
<LI><A HREF="gnat_ug.html#IDX104">Warning messages</A>
<LI><A HREF="gnat_ug.html#IDX176">Warnings</A>
<LI><A HREF="gnat_ug.html#IDX149">Writing internal trees</A>
</DIR>

</P>

<P><HR><P>
This document was generated on 2 July 1999 using the
<A HREF="http://wwwcn.cern.ch/dci/texi2html/">texi2html</A>
translator version 1.51.</P>
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