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<h3 class="section">1.3 Preprocessing and conditional compilation</h3>
<p><a name="index-CPP-4"></a><a name="index-FPP-5"></a><a name="index-Conditional-compilation-6"></a><a name="index-Preprocessing-7"></a><a name="index-preprocessor_002c-include-file-handling-8"></a>
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><span class="file">.F</span></samp>, <samp><span class="file">.FOR</span></samp>, <samp><span class="file">.FTN</span></samp>, <samp><span class="file">.fpp</span></samp>,
<samp><span class="file">.FPP</span></samp>, <samp><span class="file">.F90</span></samp>, <samp><span class="file">.F95</span></samp>, <samp><span class="file">.F03</span></samp> or <samp><span class="file">.F08</span></samp>. To manually
invoke the preprocessor on any file, use <samp><span class="option">-cpp</span></samp>, to disable
preprocessing on files where the preprocessor is run automatically, use
<samp><span class="option">-nocpp</span></samp>.
<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>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="../cpp/index.html#Top">Overview</a> for details.
<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>).
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