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<HTML>
<HEAD>
<TITLE>Limitations and Extensions</TITLE>
</HEAD>
<BODY>
<A HREF="toc.html">Table of Contents</A><P>
<P>Previous: <A HREF="sect8.html">Interpreting the Output</A><HR><P>
<H2><A NAME="sect9" HREF="toc.html#toc9">Limitations and Extensions </A></H2>
<P>
<B>ftnchek </B> accepts ANSI standard Fortran-77 programs with
some minor limitations and numerous common extensions.
<DL>
<DT><B>Limitations</B>: </DT>
<DD> <blockquote></DD>
</DL>
<P>
<B>ftnchek
</B> uses only one line of lookahead when analyzing a program into its basic
syntactic elements. If a particular statement is difficult to identify,
it may be handled improperly if the ambiguity is not resolved on a single
line. This limitation applies to complex constants except in DATA statements,
and to situations in which a variable name might be confused with a keyword.
For example, if the variable name WRITE is used for an array, then a
very long statement assigning a value to some element of this array could
be mistaken as a WRITE statement if the equals sign is not on the same
line as the word WRITE . <P>
The dummy arguments in statement functions are
treated like ordinary variables of the program. That is, their scope is
the entire module, not just the statement function definition. <P>
The checking
of FORMAT statements is lax, tolerating missing separators (comma, etc.)
between format descriptors in places where the Standard requires them,
and allowing <I>.d </I> fields on descriptors that should not have them. It does
warn under <B><A HREF="f77.html">-f77</A>=format-edit-descr </B> about nonstandard descriptor types (like
O ), and supported extensions. <P>
The only checking related to control of
execution flow is a warning about statements that cannot be reached because
they do not have a label and they follow an unconditional transfer. There
is no checking for correct nesting of DO loops or matching of opening
statements such as IF ... THEN with closing statements such as ENDIF ,
nor the proper definition and use of statement labels. Fortunately, most
compilers will catch these errors. <P>
If a user-supplied subprogram has the
same name as one of the nonstandard intrinsic functions recognized by
<B>ftnchek </B>, it must be declared in an EXTERNAL statement in any routine
that invokes it. Otherwise it will be subject to the checking normally
given to the intrinsic function. Since the nonstandard intrinsics are
not standard, this EXTERNAL statement is not required by the Fortran
77 Standard. Using the <B><A HREF="intrinsic.html">-intrinsic</A>=none </B> setting, recognition of most nonstandard
intrinsics (excepting only those needed to support the double complex
data type) can be turned off. See the lists of supported nonstandard intrinsic
functions under the discussion of the <B><A HREF="intrinsic.html">-intrinsic</A> </B> setting above. </blockquote>
<DL>
<DT><B>Extensions</B>:
</DT>
<DD>All of these extensions (except lower-case characters) will generate warnings
if the relevant <B><A HREF="f77.html">-f77</A> </B> option is set. Some of the extensions listed below
are part of the Fortran-90 Standard. These are indicated by the notation
(F90). <blockquote></DD>
</DL>
<P>
Tabs are permitted, and translated into equivalent blanks which
correspond to tab stops every 8 columns. The standard does not recognize
tabs. Note that some compilers allow tabs, but treat them differently.
The treatment defined for DEC FORTRAN can be achieved using the <B><A HREF="source.html">-source</A>=dec-tab
</B> setting. <P>
Strings may be delimited by either quote marks or apostrophes.
A sequence of two delimiter characters is interpreted as a single embedded
delimiter character. (F90) <P>
Strings may contain UNIX-style backslash escape
sequences. They will be interpreted as such if the <B><A HREF="source.html">-source</A>=unix-backslash
</B> setting is given. Otherwise the backslash character will be treated as
a normal printing character. <P>
Lower case characters are permitted, and are
converted internally to uppercase except in character strings. The standard
specifies upper case only, except in comments and strings. (F90) <P>
Hollerith
constants are permitted, in accordance with the Fortran 77 Standard, appendix
C. They should not be used in expressions, or confused with datatype CHARACTER.
<P>
The letter 'D' (upper or lower case) in column 1 is treated as the beginning
of a comment. There is no option to treat such lines as statements instead
of comments. <P>
Statements may be longer than 72 columns provided that the
setting <B><A HREF="columns.html">-columns</A> </B> was used to increase the limit. According to the standard,
all text from columns 73 through 80 is ignored, and no line may be longer
than 80 columns. <P>
Variable names may be longer than six characters. The
standard specifies six as the maximum. <B>ftnchek </B> permits names up to 31
characters long (F90). <P>
Variable names may contain underscores and dollar
signs, which are treated the same as alphabetic letters. The default type
for variables beginning with these characters is REAL. In IMPLICIT type
statements specifying a range of characters, the dollar sign follows Z
and is followed by underscore. Fortran 90 permits underscores in variable
names. <P>
The UNIX version tolerates the presence of preprocessor directives,
namely lines beginning with the pound sign (#). These are treated as comments,
except for #line directives, which are interpreted, and are used to set
the line number and source file name for warnings and error messages.
Note that #include directives are not processed by <B>ftnchek </B>. Programs
that use them for including source files should be passed through the
preprocessor before being input to <B>ftnchek </B>. As noted below, <B>ftnchek </B> does
process INCLUDE statements, which have a different syntax. An optional
program, <B><A HREF="/cgi-bin/man2html?ftnpp&1L">ftnpp </B>(1L)</A>
is provided with the <B>ftnchek </B> distribution to provide
preprocessing that properly handles INCLUDE files. <P>
The Fortran 90 DO
... ENDDO control structure is permitted. The CYCLE and EXIT statements
are accepted. All of these may have an optional do-construct name, but
construct names are not checked for consistency. (F90) <P>
Construct names
are also accepted on IF , THEN , ELSE , and ENDIF statements. (F90) <P>
The
ACCEPT and TYPE statements (for terminal I/O) are permitted, with the
same syntax as PRINT . <P>
The so-called ``Cray pointer'' syntax is tolerated. It
is not the same as the Fortran 90 POINTER statement. There is no real
checking of the statement other than basic syntax. The form of this statement
is POINTER ( <I>pointer </I>, <I>pointee </I>) [,( <I>pointer </I>, <I>pointee </I>) ] The pointer
variables are assigned a data type of INTEGER *4 . Usage checking of the
pointee variables is suppressed, since in practice they are accessed indirectly
via the pointers. <P>
Statements may have any number of continuation lines.
The Fortran 77 standard allows a maximum of 19. <P>
Relational (comparison)
operators composed of punctuation, namely: < <= == /= > >= are allowed. (F90)
<P>
Inline comments, beginning with an exclamation mark, are permitted. (F90)
<P>
NAMELIST I/O is supported. The syntax is the same as in Fortran 90. <P>
FORMAT
statements can contain a dollar sign to indicate suppression of carriage-return.
An integer expression enclosed in angle brackets can be used anywhere
in a FORMAT statement where the Fortran 77 Standard allows an integer
constant (except for the length of a Hollerith constant), to provide a
run-time value for a repeat specification or field width. <P>
Nonstandard keywords
are allowed in I/O statements, corresponding to those in VMS Fortran. <P>
The
IMPLICIT NONE statement is supported. The meaning of this statement is
that all variables must have their data types explicitly declared. Rather
than flag the occurrences of such variables with syntax error messages,
<B>ftnchek </B> waits till the end of the module, and then prints out a list
of all undeclared variables, as it does for the <B><A HREF="declare.html">-declare</A> </B> option. (F90)
<P>
Data types INTEGER , REAL , COMPLEX , and LOGICAL are allowed to have
an optional precision specification in type declarations. For instance,
REAL*8 means an 8-byte floating point data type. The REAL*8 datatype
is not necessarily considered equivalent to DOUBLE PRECISION , depending
on the <B><A HREF="wordsize.html">-wordsize</A> </B> setting. The Fortran 77 Standard allows a length specification
only for CHARACTER data. <P>
<B>ftnchek </B> supports the DOUBLE COMPLEX type specification
for a complex quantity whose real and imaginary parts are double precision.
Mixed-mode arithmetic involving single-precision complex with double-precision
real data, prohibited under the Standard, yields a double complex result.
<P>
Many commonly found nonstandard intrinsic functions are provided. See
the discussion of <B><A HREF="intrinsic.html">-intrinsic</A> </B> for a list of functions and how to control
which ones are recognized.. <P>
Argument checking is not tight for those nonstandard
intrinsics that take arrays or mixed argument types. <P>
<B>ftnchek </B> permits the
INCLUDE statement, which causes inclusion of the text of the given file.
The syntax is INCLUDE ' <I>filename </I>' <P>
This is compatible with Fortran 90.
If the <B><A HREF="source.html">-source</A>=vms-include </B> option is given, <B>ftnchek </B> follows VMS conventions
with respect to this statement: it assumes a default extension of <I>.for
</I> if no filename extension is given, and allows the qualifier /[NO]LIST
following the filename, to control the listing of the included file.
There is no support for including VMS text modules. <P>
In diagnostic output
relating to items contained in include files, the location of the error
is specified by both its location in the include file and the location
in the parent file where the file was included. <P>
<B>ftnchek </B> accepts PARAMETER
statements which lack parentheses. These will be warned about if the
<B><A HREF="f77.html">-f77</A>=param-noparen </B> flag is given. <P>
<B>ftnchek </B> accepts PARAMETER definitions
that involve intrinsic functions and exponentiation by a non-integer exponent.
Both of these cases are prohibited by the Fortran 77 Standard, and will
be warned about if the <B><A HREF="f77.html">-f77</A>=param-intrinsic </B> flag is given. If an intrinsic
function value is a compile-time integer constant, <B>ftnchek </B> will evaluate
it. This allows better checking if the parameter is used in declaring
array sizes. Fortran 90 allows intrinsic functions in PARAMETER definitions.
<P>
The intrinsic functions that are evaluated are: <CENTER> <TABLE BORDER=0>
<TR> <TD ALIGN=LEFT>ABS </TD> <TD ALIGN=LEFT>IABS </TD> <TD ALIGN=LEFT>DIM </TD> <TD ALIGN=LEFT>IDIM
</TD> <TD ALIGN=LEFT>MAX </TD> </TR>
<TR> <TD ALIGN=LEFT>MAX0 </TD> <TD ALIGN=LEFT>MIN </TD> <TD ALIGN=LEFT>MIN0 </TD> <TD ALIGN=LEFT>MOD </TD> <TD ALIGN=LEFT>SIGN </TD> </TR>
<TR> <TD ALIGN=LEFT>ISIGN </TD> <TD ALIGN=LEFT>LEN </TD> <TD ALIGN=LEFT>ICHAR </TD> <TD ALIGN=LEFT>INDEX </TD> </TR>
</TABLE>
</CENTER> <P>
The
functions of integer arguments are evaluated only if the arguments are
integer constant expressions. (These may involve integer constants, parameters,
and evaluated intrinsic functions.) The function LEN is evaluated if
its argument is an expression involving only character constants and variables
whose length is not adjustable. The functions ICHAR and INDEX are evaluated
only if the arguments are character constants. <B>ftnchek </B> gives a warning
if it needs the value of some intrinsic function that is not evaluated.
</blockquote>
<P><HR><P>Next: <A HREF="sect10.html">New Features </A>
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