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configure.in
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<div class="SECT1">
<h1 class="SECT1">
<a name="Z69"><tt class="FILENAME">configure.in</tt></a>
</h1>
<p>
<tt class="APPLICATION">autoconf</tt> processes <tt class=
"FILENAME">configure.in</tt> to produce a <tt class=
"FILENAME">configure</tt> script. <tt class="FILENAME">
configure</tt> is a portable shell script which examines
the build environment to determine which libraries are
available, which features the platform has, where libraries
and headers are located, and so on. Based on this
information, it modifies compiler flags, generates
makefiles, and/or outputs the file <tt class="FILENAME">
config.h</tt> with appropriate preprocessor symbols
defined. Again, <tt class="FILENAME">configure</tt> does
not require <tt class="APPLICATION">autoconf</tt> to run;
you generate it before distributing your software, so users
do not have to have <tt class="APPLICATION">autoconf</tt>.
</p>
<p>
Your job is to write <tt class="FILENAME">
configure.in</tt>. The file is basically a series of <tt
class="APPLICATION">m4</tt> macros, which expand to
snippets of shell script according to the parameters you
pass them. You can also write shell code manually. Really
understanding how to write a <tt class="FILENAME">
configure.in</tt> requires some knowledge of <tt class=
"APPLICATION">m4</tt> (which is pretty simple) and some
knowledge of the Bourne shell (which is a black art).
Fortunately, you can cheat: start with an existing <tt
class="FILENAME">configure.in</tt> and modify it slightly
to suit your application. There's also an extensive <tt
class="APPLICATION">autoconf</tt> manual, which describes
the many pre-written macros shipped with <tt class=
"APPLICATION">autoconf</tt>.
</p>
<p>
The GTK+ and Gnome developers have simplified things still
further, by providing macros to locate GTK+ and Gnome on
the user's system.
</p>
<p>
Here is a sample <tt class="FILENAME">configure.in</tt>,
from a Gnome version of "Hello, World":
</p>
<table border="0" bgcolor="#E0E0E0" width="100%">
<tr>
<td>
<pre class="PROGRAMLISTING">
AC_INIT(src/hello.c)
AM_CONFIG_HEADER(config.h)
AM_INIT_AUTOMAKE(GnomeHello, 0.1)
AM_MAINTAINER_MODE
AM_ACLOCAL_INCLUDE(macros)
GNOME_INIT
AC_PROG_CC
AC_ISC_POSIX
AC_HEADER_STDC
AC_ARG_PROGRAM
AM_PROG_LIBTOOL
GNOME_COMPILE_WARNINGS
ALL_LINGUAS="da de es fr gl nl no pl ru sv fi uk"
AM_GNU_GETTEXT
AC_SUBST(CFLAGS)
AC_SUBST(CPPFLAGS)
AC_SUBST(LDFLAGS)
AC_OUTPUT([
Makefile
macros/Makefile
src/Makefile
intl/Makefile
po/Makefile.in
pixmaps/Makefile
doc/Makefile
doc/C/Makefile
doc/es/Makefile
])
</pre>
</td>
</tr>
</table>
<p>
Before describing each macro, some general points should be
made. First, those macros that begin with <tt class=
"APPLICATION">AC</tt> come with <tt class="APPLICATION">
autoconf</tt>, and those that begin with <tt class=
"APPLICATION">AM</tt> usually come with <tt class=
"APPLICATION">automake</tt>. (This is useful when you're
trying to find documentation for them.) The macros that
begin with <tt class="APPLICATION">GNOME</tt> come in the
Gnome <tt class="FILENAME">macros</tt> directory. These
macros are written in <tt class="APPLICATION">m4</tt>; the
standard ones from <tt class="APPLICATION">
autoconf</tt>/<tt class="APPLICATION">automake</tt> reside
in <tt class="FILENAME">/usr/share/aclocal</tt>, if you
installed <tt class="APPLICATION">autoconf</tt>/<tt class=
"APPLICATION">automake</tt> under <tt class="FILENAME">
/usr</tt>. (An aside: the <tt class="FILENAME">macros</tt>
directory is not a good thing; each Gnome package should
install its own <tt class="APPLICATION">m4</tt> files to
<tt class="FILENAME">/usr/share/aclocal</tt>. Newer Gnome
versions attempt to fix the problem.)
</p>
<ul>
<li>
<p>
<span class="SYMBOL">AC_INIT</span> is always the first
macro in <tt class="FILENAME">configure.in</tt>. It
expands to a lot of boilerplate code shared by all <tt
class="FILENAME">configure</tt> scripts; this code
parses the command line arguments to <tt class=
"FILENAME">configure</tt>. The macro's one argument is
a file that should be present in the source directory;
this is used as a sanity check, to be sure <tt class=
"FILENAME">configure</tt> has correctly located the
source directory.
</p>
</li>
<li>
<p>
<span class="SYMBOL">AM_CONFIG_HEADER</span> specifies
a header file to create; this will almost always be <tt
class="FILENAME">config.h</tt>. The created header file
will contain C preprocessor symbols defined by <tt
class="FILENAME">configure</tt>. At a minimum, the
symbols <span class="STRUCTNAME">PACKAGE</span> and
<span class="STRUCTNAME">VERSION</span> will be
defined, which makes it easy to put the name and
version of your program in your code without
hard-coding them. (Your non-public source files should
<tt class="APPLICATION">#include <config.h></tt>
to take advantage of its definitions; however, <tt
class="APPLICATION">config.h</tt> should never be
installed, because it would conflict with other
packages.)
</p>
</li>
<li>
<p>
<span class="SYMBOL">AM_INIT_AUTOMAKE</span>
initializes <tt class="APPLICATION">automake</tt>; the
arguments to this macro are the name and version of the
package being compiled. (These arguments become the
values of <span class="STRUCTNAME">PACKAGE</span> and
<span class="STRUCTNAME">VERSION</span>, defined in <tt
class="FILENAME">config.h</tt>.)
</p>
</li>
<li>
<p>
<span class="SYMBOL">AM_MAINTAINER_MODE</span> turns
off maintainer-only makefile targets by default, and
changes <tt class="FILENAME">configure</tt> to
understand a <tt class="APPLICATION">
--enable-maintainer-mode</tt> option. <tt class=
"APPLICATION">--enable-maintainer-mode</tt> turns the
maintainer-only targets back on. The maintainer-only
makefile targets permit end users to clean
automatically-generated files such as <tt class=
"FILENAME">configure</tt>, which means they have to
have <tt class="APPLICATION">autoconf</tt> and <tt
class="APPLICATION">automake</tt> installed to repair
the damage. <span class="SYMBOL">
AM_MAINTAINER_MODE</span> makes it a bit harder for
users to shoot themselves in the foot. Note, however,
that the <tt class="FILENAME">autogen.sh</tt> script
used in Gnome automatically passes <tt class=
"APPLICATION">--enable-maintainer-mode</tt> to <tt
class="FILENAME">configure</tt>, since <tt class=
"FILENAME">autogen.sh</tt> is intended for developers
to use.
</p>
</li>
<li>
<p>
<span class="SYMBOL">AM_ACLOCAL_INCLUDE</span>
specifies an additional directory in which to search
for <tt class="APPLICATION">m4</tt> macros. In this
case, it specifies the <tt class="FILENAME">macros</tt>
subdirectory, where you should have copied the Gnome
macros.
</p>
</li>
<li>
<p>
<span class="SYMBOL">GNOME_INIT</span> adds a number of
Gnome-related command-line arguments to <tt class=
"FILENAME">configure</tt>, and defines makefile
variables containing the necessary preprocessor and
linker flags for Gnome programs. These flags are
obtained from a <tt class="APPLICATION">
gnome-config</tt> script installed by the <tt class=
"APPLICATION">gnome-libs</tt> package.
</p>
</li>
<li>
<p>
<span class="SYMBOL">AC_PROG_CC</span> locates the C
compiler.
</p>
</li>
<li>
<p>
<span class="SYMBOL">AC_ISC_POSIX</span> adds some
flags needed for POSIX compatibility on certain
platforms.
</p>
</li>
<li>
<p>
<span class="SYMBOL">AC_HEADER_STDC</span> checks
whether the present system has the standard ANSI header
files, and defines <tt class="FUNCTION">
STDC_HEADERS</tt> if so.
</p>
</li>
<li>
<p>
<span class="SYMBOL">AC_ARG_PROGRAM</span> adds options
to <tt class="FILENAME">configure</tt> so that users
can modify the name of an installed program. (Useful if
your program happens to have the same name as some
locally-installed program on their system.)
</p>
</li>
<li>
<p>
<span class="SYMBOL">AM_PROG_LIBTOOL</span> is used by
<tt class="APPLICATION">automake</tt> to set up its use
of <tt class="APPLICATION">libtool</tt>. This is only
required if you are planning to build a shared library
or dynamically loadable modules; it is unnecessary for
this early version of GnomeHello, but we're planning
ahead.
</p>
</li>
<li>
<p>
<span class="SYMBOL">GNOME_COMPILE_WARNINGS</span> adds
a number of warning options to the <tt class=
"APPLICATION">gcc</tt> command line, but does nothing
for most other compilers.
</p>
</li>
<li>
<p>
<tt class="APPLICATION">ALL_LINGUAS="es"</tt> is not a
macro, just a bit of shell code. It contains a
space-separated list of language abbreviations,
corresponding to <tt class="APPLICATION">.po</tt> files
in the <tt class="APPLICATION">po</tt> subdirectory.
(<tt class="APPLICATION">.po</tt> files contain
translations into other languages, so <tt class=
"APPLICATION">ALL_LINGUAS</tt> should list all
languages your program has been translated into.)
</p>
</li>
<li>
<p>
<span class="SYMBOL">AM_GNU_GETTEXT</span> is used by
<tt class="APPLICATION">automake</tt>, but the macro
itself is distributed with the <tt class="APPLICATION">
gettext</tt> package. It causes <tt class=
"APPLICATION">automake</tt> to perform a number of
internationalization-related tasks.
</p>
</li>
<li>
<p>
<span class="SYMBOL">AC_SUBST</span> "exports" a
variable into the files generated by <tt class=
"FILENAME">configure</tt>. More on this below.
</p>
</li>
<li>
<p>
<span class="SYMBOL">AC_OUTPUT</span> lists the files
to be created by the <tt class="FILENAME">
configure</tt> script. These will be created from a
file with the same name, with <tt class="APPLICATION">
.in</tt> appended. For example, the output file <tt
class="APPLICATION">src/Makefile</tt> is generated from
<tt class="APPLICATION">src/Makefile.in</tt>, and <tt
class="APPLICATION">config.h</tt> comes from <tt class=
"APPLICATION">config.h.in</tt>.
</p>
</li>
</ul>
<p>
In the <tt class="APPLICATION">AC_OUTPUT</tt> stage, <tt
class="APPLICATION">configure</tt> processes files
containing variables marked with two <tt class=
"APPLICATION">@</tt> symbols; for example, <tt class=
"APPLICATION">@PACKAGE@</tt>. It recognizes such variables
only if <span class="SYMBOL">AC_SUBST</span> was used to
"export" the variable (many of the pre-written macros
discussed above use <span class="SYMBOL">AC_SUBST</span> to
define variables). Most commonly, this features is used to
convert a <tt class="FILENAME">Makefile.in</tt> to a <tt
class="FILENAME">Makefile</tt>. <tt class="FILENAME">
Makefile.in</tt> is typically generated by <tt class=
"APPLICATION">automake</tt> from <tt class="FILENAME">
Makefile.am</tt>. (However, you can use <tt class=
"APPLICATION">autoconf</tt> without <tt class=
"APPLICATION">automake</tt>, and write <tt class=
"FILENAME">Makefile.in</tt> yourself.)
</p>
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