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<title>The GNU Fortran Compiler: Preprocessing and conditional compilation</title>

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<a name="Preprocessing-and-conditional-compilation"></a>
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Next: <a href="GNU-Fortran-and-G77.html#GNU-Fortran-and-G77" accesskey="n" rel="next">GNU Fortran and G77</a>, Previous: <a href="GNU-Fortran-and-GCC.html#GNU-Fortran-and-GCC" accesskey="p" rel="prev">GNU Fortran and GCC</a>, Up: <a href="Introduction.html#Introduction" accesskey="u" rel="up">Introduction</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Preprocessing-and-conditional-compilation-1"></a>
<h3 class="section">1.3 Preprocessing and conditional compilation</h3>
<a name="index-CPP"></a>
<a name="index-FPP"></a>
<a name="index-Conditional-compilation"></a>
<a name="index-Preprocessing"></a>
<a name="index-preprocessor_002c-include-file-handling"></a>

<p>Many Fortran compilers including GNU Fortran allow passing the source code
through a C preprocessor (CPP; sometimes also called the Fortran preprocessor,
FPP) to allow for conditional compilation.  In the case of GNU Fortran,
this is the GNU C Preprocessor in the traditional mode.  On systems with
case-preserving file names, the preprocessor is automatically invoked if the
filename extension is <samp>.F</samp>, <samp>.FOR</samp>, <samp>.FTN</samp>, <samp>.fpp</samp>,
<samp>.FPP</samp>, <samp>.F90</samp>, <samp>.F95</samp>, <samp>.F03</samp> or <samp>.F08</samp>.  To manually
invoke the preprocessor on any file, use <samp>-cpp</samp>, to disable
preprocessing on files where the preprocessor is run automatically, use
<samp>-nocpp</samp>.
</p>
<p>If a preprocessed file includes another file with the Fortran <code>INCLUDE</code>
statement, the included file is not preprocessed.  To preprocess included
files, use the equivalent preprocessor statement <code>#include</code>.
</p>
<p>If GNU Fortran invokes the preprocessor, <code>__GFORTRAN__</code>
is defined and <code>__GNUC__</code>, <code>__GNUC_MINOR__</code> and
<code>__GNUC_PATCHLEVEL__</code> can be used to determine the version of the
compiler.  See <a href="http://gcc.gnu.org/onlinedocs/cpp/index.html#Top">Overview</a> in <cite>The C Preprocessor</cite> for details.
</p>
<p>While CPP is the de-facto standard for preprocessing Fortran code,
Part 3 of the Fortran 95 standard (ISO/IEC 1539-3:1998) defines
Conditional Compilation, which is not widely used and not directly
supported by the GNU Fortran compiler.  You can use the program coco
to preprocess such files (<a href="http://www.daniellnagle.com/coco.html">http://www.daniellnagle.com/coco.html</a>).
</p>


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