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<h3 class="section">2.3 Enable and customize preprocessing</h3>
<p><a name="index-preprocessor-54"></a><a name="index-options_002c-preprocessor-55"></a><a name="index-CPP-56"></a>
Preprocessor related options. See section
<a href="Preprocessing-and-conditional-compilation.html#Preprocessing-and-conditional-compilation">Preprocessing and conditional compilation</a> for more detailed
information on preprocessing in <samp><span class="command">gfortran</span></samp>.
<dl>
<dt><code>-cpp</code><dt><code>-nocpp</code><dd><a name="index-g_t_0040code_007bcpp_007d-57"></a><a name="index-g_t_0040code_007bfpp_007d-58"></a><a name="index-preprocessor_002c-enable-59"></a><a name="index-preprocessor_002c-disable-60"></a>Enable preprocessing. The preprocessor is automatically invoked if
the file extension is <samp><span class="file">.fpp</span></samp>, <samp><span class="file">.FPP</span></samp>, <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">.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>. Use
this option to manually enable preprocessing of any kind of Fortran file.
<p>To disable preprocessing of files with any of the above listed extensions,
use the negative form: <samp><span class="option">-nocpp</span></samp>.
<p>The preprocessor is run in traditional mode. Any restrictions of the
file-format, especially the limits on line length, apply for
preprocessed output as well, so it might be advisable to use the
<samp><span class="option">-ffree-line-length-none</span></samp> or <samp><span class="option">-ffixed-line-length-none</span></samp>
options.
<br><dt><code>-dM</code><dd><a name="index-g_t_0040code_007bdM_007d-61"></a><a name="index-preprocessor_002c-debugging-62"></a><a name="index-debugging_002c-preprocessor-63"></a>Instead of the normal output, generate a list of <code>'#define'</code>
directives for all the macros defined during the execution of the
preprocessor, including predefined macros. This gives you a way
of finding out what is predefined in your version of the preprocessor.
Assuming you have no file <samp><span class="file">foo.f90</span></samp>, the command
<pre class="smallexample"> touch foo.f90; gfortran -cpp -E -dM foo.f90
</pre>
<p>will show all the predefined macros.
<br><dt><code>-dD</code><dd><a name="index-g_t_0040code_007bdD_007d-64"></a><a name="index-preprocessor_002c-debugging-65"></a><a name="index-debugging_002c-preprocessor-66"></a>Like <samp><span class="option">-dM</span></samp> except in two respects: it does not include the
predefined macros, and it outputs both the <code>#define</code> directives
and the result of preprocessing. Both kinds of output go to the
standard output file.
<br><dt><code>-dN</code><dd><a name="index-g_t_0040code_007bdN_007d-67"></a><a name="index-preprocessor_002c-debugging-68"></a><a name="index-debugging_002c-preprocessor-69"></a>Like <samp><span class="option">-dD</span></samp>, but emit only the macro names, not their expansions.
<br><dt><code>-dU</code><dd><a name="index-g_t_0040code_007bdU_007d-70"></a><a name="index-preprocessor_002c-debugging-71"></a><a name="index-debugging_002c-preprocessor-72"></a>Like <samp><span class="option">dD</span></samp> except that only macros that are expanded, or whose
definedness is tested in preprocessor directives, are output; the
output is delayed until the use or test of the macro; and <code>'#undef'</code>
directives are also output for macros tested but undefined at the time.
<br><dt><code>-dI</code><dd><a name="index-g_t_0040code_007bdI_007d-73"></a><a name="index-preprocessor_002c-debugging-74"></a><a name="index-debugging_002c-preprocessor-75"></a>Output <code>'#include'</code> directives in addition to the result
of preprocessing.
<br><dt><code>-fworking-directory</code><dd><a name="index-g_t_0040code_007bfworking_002ddirectory_007d-76"></a><a name="index-preprocessor_002c-working-directory-77"></a>Enable generation of linemarkers in the preprocessor output that will
let the compiler know the current working directory at the time of
preprocessing. When this option is enabled, the preprocessor will emit,
after the initial linemarker, a second linemarker with the current
working directory followed by two slashes. GCC will use this directory,
when it's present in the preprocessed input, as the directory emitted
as the current working directory in some debugging information formats.
This option is implicitly enabled if debugging information is enabled,
but this can be inhibited with the negated form
<samp><span class="option">-fno-working-directory</span></samp>. If the <samp><span class="option">-P</span></samp> flag is present
in the command line, this option has no effect, since no <code>#line</code>
directives are emitted whatsoever.
<br><dt><code>-idirafter </code><var>dir</var><dd><a name="index-g_t_0040code_007bidirafter-_0040var_007bdir_007d_007d-78"></a><a name="index-preprocessing_002c-include-path-79"></a>Search <var>dir</var> for include files, but do it after all directories
specified with <samp><span class="option">-I</span></samp> and the standard system directories have
been exhausted. <var>dir</var> is treated as a system include directory.
If dir begins with <code>=</code>, then the <code>=</code> will be replaced by
the sysroot prefix; see <samp><span class="option">--sysroot</span></samp> and <samp><span class="option">-isysroot</span></samp>.
<br><dt><code>-imultilib </code><var>dir</var><dd><a name="index-g_t_0040code_007bimultilib-_0040var_007bdir_007d_007d-80"></a><a name="index-preprocessing_002c-include-path-81"></a>Use <var>dir</var> as a subdirectory of the directory containing target-specific
C++ headers.
<br><dt><code>-iprefix </code><var>prefix</var><dd><a name="index-g_t_0040code_007biprefix-_0040var_007bprefix_007d_007d-82"></a><a name="index-preprocessing_002c-include-path-83"></a>Specify <var>prefix</var> as the prefix for subsequent <samp><span class="option">-iwithprefix</span></samp>
options. If the <var>prefix</var> represents a directory, you should include
the final <code>'/'</code>.
<br><dt><code>-isysroot </code><var>dir</var><dd><a name="index-g_t_0040code_007bisysroot-_0040var_007bdir_007d_007d-84"></a><a name="index-preprocessing_002c-include-path-85"></a>This option is like the <samp><span class="option">--sysroot</span></samp> option, but applies only to
header files. See the <samp><span class="option">--sysroot</span></samp> option for more information.
<br><dt><code>-iquote </code><var>dir</var><dd><a name="index-g_t_0040code_007biquote-_0040var_007bdir_007d_007d-86"></a><a name="index-preprocessing_002c-include-path-87"></a>Search <var>dir</var> only for header files requested with <code>#include "file"</code>;
they are not searched for <code>#include <file></code>, before all directories
specified by <samp><span class="option">-I</span></samp> and before the standard system directories. If
<var>dir</var> begins with <code>=</code>, then the <code>=</code> will be replaced by the
sysroot prefix; see <samp><span class="option">--sysroot</span></samp> and <samp><span class="option">-isysroot</span></samp>.
<br><dt><code>-isystem </code><var>dir</var><dd><a name="index-g_t_0040code_007bisystem-_0040var_007bdir_007d_007d-88"></a><a name="index-preprocessing_002c-include-path-89"></a>Search <var>dir</var> for header files, after all directories specified by
<samp><span class="option">-I</span></samp> but before the standard system directories. Mark it as a
system directory, so that it gets the same special treatment as is
applied to the standard system directories. If <var>dir</var> begins with
<code>=</code>, then the <code>=</code> will be replaced by the sysroot prefix;
see <samp><span class="option">--sysroot</span></samp> and <samp><span class="option">-isysroot</span></samp>.
<br><dt><code>-nostdinc</code><dd><a name="index-g_t_0040code_007bnostdinc_007d-90"></a>Do not search the standard system directories for header files. Only
the directories you have specified with <samp><span class="option">-I</span></samp> options (and the
directory of the current file, if appropriate) are searched.
<br><dt><code>-undef</code><dd><a name="index-g_t_0040code_007bundef_007d-91"></a>Do not predefine any system-specific or GCC-specific macros.
The standard predefined macros remain defined.
<br><dt><code>-A</code><var>predicate</var><code>=</code><var>answer</var><dd><a name="index-g_t_0040code_007bA_0040var_007bpredicate_007d_003d_0040var_007banswer_007d_007d-92"></a><a name="index-preprocessing_002c-assertion-93"></a>Make an assertion with the predicate <var>predicate</var> and answer <var>answer</var>.
This form is preferred to the older form -A predicate(answer), which is still
supported, because it does not use shell special characters.
<br><dt><code>-A-</code><var>predicate</var><code>=</code><var>answer</var><dd><a name="index-g_t_0040code_007bA_002d_0040var_007bpredicate_007d_003d_0040var_007banswer_007d_007d-94"></a><a name="index-preprocessing_002c-assertion-95"></a>Cancel an assertion with the predicate <var>predicate</var> and answer <var>answer</var>.
<br><dt><code>-C</code><dd><a name="index-g_t_0040code_007bC_007d-96"></a><a name="index-preprocessing_002c-keep-comments-97"></a>Do not discard comments. All comments are passed through to the output
file, except for comments in processed directives, which are deleted
along with the directive.
<p>You should be prepared for side effects when using <samp><span class="option">-C</span></samp>; it causes
the preprocessor to treat comments as tokens in their own right. For example,
comments appearing at the start of what would be a directive line have the
effect of turning that line into an ordinary source line, since the first
token on the line is no longer a <code>'#'</code>.
<p>Warning: this currently handles C-Style comments only. The preprocessor
does not yet recognize Fortran-style comments.
<br><dt><code>-CC</code><dd><a name="index-g_t_0040code_007bCC_007d-98"></a><a name="index-preprocessing_002c-keep-comments-99"></a>Do not discard comments, including during macro expansion. This is like
<samp><span class="option">-C</span></samp>, except that comments contained within macros are also passed
through to the output file where the macro is expanded.
<p>In addition to the side-effects of the <samp><span class="option">-C</span></samp> option, the <samp><span class="option">-CC</span></samp>
option causes all C++-style comments inside a macro to be converted to C-style
comments. This is to prevent later use of that macro from inadvertently
commenting out the remainder of the source line. The <samp><span class="option">-CC</span></samp> option
is generally used to support lint comments.
<p>Warning: this currently handles C- and C++-Style comments only. The
preprocessor does not yet recognize Fortran-style comments.
<br><dt><code>-D</code><var>name</var><dd><a name="index-g_t_0040code_007bD_0040var_007bname_007d_007d-100"></a><a name="index-preprocessing_002c-define-macros-101"></a>Predefine name as a macro, with definition <code>1</code>.
<br><dt><code>-D</code><var>name</var><code>=</code><var>definition</var><dd><a name="index-g_t_0040code_007bD_0040var_007bname_007d_003d_0040var_007bdefinition_007d_007d-102"></a><a name="index-preprocessing_002c-define-macros-103"></a>The contents of <var>definition</var> are tokenized and processed as if they
appeared during translation phase three in a <code>'#define'</code> directive.
In particular, the definition will be truncated by embedded newline
characters.
<p>If you are invoking the preprocessor from a shell or shell-like program
you may need to use the shell's quoting syntax to protect characters such
as spaces that have a meaning in the shell syntax.
<p>If you wish to define a function-like macro on the command line, write
its argument list with surrounding parentheses before the equals sign
(if any). Parentheses are meaningful to most shells, so you will need
to quote the option. With sh and csh, <code>-D'name(args...)=definition'</code>
works.
<p><samp><span class="option">-D</span></samp> and <samp><span class="option">-U</span></samp> options are processed in the order they are
given on the command line. All -imacros file and -include file options
are processed after all -D and -U options.
<br><dt><code>-H</code><dd><a name="index-g_t_0040code_007bH_007d-104"></a>Print the name of each header file used, in addition to other normal
activities. Each name is indented to show how deep in the <code>'#include'</code>
stack it is.
<br><dt><code>-P</code><dd><a name="index-g_t_0040code_007bP_007d-105"></a><a name="index-preprocessing_002c-no-linemarkers-106"></a>Inhibit generation of linemarkers in the output from the preprocessor.
This might be useful when running the preprocessor on something that
is not C code, and will be sent to a program which might be confused
by the linemarkers.
<br><dt><code>-U</code><var>name</var><dd><a name="index-g_t_0040code_007bU_0040var_007bname_007d_007d-107"></a><a name="index-preprocessing_002c-undefine-macros-108"></a>Cancel any previous definition of <var>name</var>, either built in or provided
with a <samp><span class="option">-D</span></samp> option.
</dl>
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