preprocessor-options.html

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     <br><dt><code>-M</code>
     <dd>Instead of outputting the result of preprocessing, output a rule
suitable for <code>make</code> describing the dependencies of the main
source file.  The preprocessor outputs one <code>make</code> rule containing
the object file name for that source file, a colon, and the names of all
the included files, including those coming from <code>-include</code> or
<code>-imacros</code> command line options.

     <p>Unless specified explicitly (with <code>-MT</code> or <code>-MQ</code>), the
object file name consists of the basename of the source file with any
suffix replaced with object file suffix.  If there are many included
files then the rule is split into several lines using <code>\</code>-newline. 
The rule has no commands.

     <p>This option does not suppress the preprocessor's debug output, such as
<code>-dM</code>.  To avoid mixing such debug output with the dependency
rules you should explicitly specify the dependency output file with
<code>-MF</code>, or use an environment variable like
<code>DEPENDENCIES_OUTPUT</code> (see <a href="Environment-Variables.html#Environment%20Variables">Environment Variables</a>).  Debug output
will still be sent to the regular output stream as normal.

     <p>Passing <code>-M</code> to the driver implies <code>-E</code>, and suppresses
warnings with an implicit <code>-w</code>.

     <br><dt><code>-MM</code>
     <dd>Like <code>-M</code> but do not mention header files that are found in
system header directories, nor header files that are included,
directly or indirectly, from such a header.

     <p>This implies that the choice of angle brackets or double quotes in an
<code>#include</code> directive does not in itself determine whether that
header will appear in <code>-MM</code> dependency output.  This is a
slight change in semantics from GCC versions 3.0 and earlier.

     <p><a name="dashMF"></a>
<br><dt><code>-MF </code><var>file</var><code></code>
     <dd>When used with <code>-M</code> or <code>-MM</code>, specifies a
file to write the dependencies to.  If no <code>-MF</code> switch is given
the preprocessor sends the rules to the same place it would have sent
preprocessed output.

     <p>When used with the driver options <code>-MD</code> or <code>-MMD</code>,
<code>-MF</code> overrides the default dependency output file.

     <br><dt><code>-MG</code>
     <dd>In conjunction with an option such as <code>-M</code> requesting
dependency generation, <code>-MG</code> assumes missing header files are
generated files and adds them to the dependency list without raising
an error.  The dependency filename is taken directly from the
<code>#include</code> directive without prepending any path.  <code>-MG</code>
also suppresses preprocessed output, as a missing header file renders
this useless.

     <p>This feature is used in automatic updating of makefiles.

     <br><dt><code>-MP</code>
     <dd>This option instructs CPP to add a phony target for each dependency
other than the main file, causing each to depend on nothing.  These
dummy rules work around errors <code>make</code> gives if you remove header
files without updating the <code>Makefile</code> to match.

     <p>This is typical output:

     <pre class="smallexample">          test.o: test.c test.h
          
          test.h:
          </pre>

     <br><dt><code>-MT </code><var>target</var><code></code>
     <dd>

     <p>Change the target of the rule emitted by dependency generation.  By
default CPP takes the name of the main input file, including any path,
deletes any file suffix such as <code>.c</code>, and appends the platform's
usual object suffix.  The result is the target.

     <p>An <code>-MT</code> option will set the target to be exactly the string you
specify.  If you want multiple targets, you can specify them as a single
argument to <code>-MT</code>, or use multiple <code>-MT</code> options.

     <p>For example, <code>-MT&nbsp;'$(objpfx)foo.o'</code> might give

     <pre class="smallexample">          $(objpfx)foo.o: foo.c
          </pre>

     <br><dt><code>-MQ </code><var>target</var><code></code>
     <dd>

     <p>Same as <code>-MT</code>, but it quotes any characters which are special to
Make.  <code>-MQ&nbsp;'$(objpfx)foo.o'</code> gives

     <pre class="smallexample">          $$(objpfx)foo.o: foo.c
          </pre>

     <p>The default target is automatically quoted, as if it were given with
<code>-MQ</code>.

     <br><dt><code>-MD</code>
     <dd><code>-MD</code> is equivalent to <code>-M -MF </code><var>file</var><code></code>, except that
<code>-E</code> is not implied.  The driver determines <var>file</var> based on
whether an <code>-o</code> option is given.  If it is, the driver uses its
argument but with a suffix of <code>.d</code>, otherwise it take the
basename of the input file and applies a <code>.d</code> suffix.

     <p>If <code>-MD</code> is used in conjunction with <code>-E</code>, any
<code>-o</code> switch is understood to specify the dependency output file
(but see <a href="dashMF.html#dashMF">-MF</a>), but if used without <code>-E</code>, each <code>-o</code>
is understood to specify a target object file.

     <p>Since <code>-E</code> is not implied, <code>-MD</code> can be used to generate
a dependency output file as a side-effect of the compilation process.

     <br><dt><code>-MMD</code>
     <dd>Like <code>-MD</code> except mention only user header files, not system
-header files.

     <br><dt><code>-fpch-deps</code>
     <dd>When using precompiled headers (see <a href="Precompiled-Headers.html#Precompiled%20Headers">Precompiled Headers</a>), this flag
will cause the dependency-output flags to also list the files from the
precompiled header's dependencies.  If not specified only the
precompiled header would be listed and not the files that were used to
create it because those files are not consulted when a precompiled
header is used.

     <br><dt><code>-x c</code>
     <dd><dt><code>-x c++</code>
     <dd><dt><code>-x objective-c</code>
     <dd><dt><code>-x assembler-with-cpp</code>
     <dd>Specify the source language: C, C++, Objective-C, or assembly.  This has
nothing to do with standards conformance or extensions; it merely
selects which base syntax to expect.  If you give none of these options,
cpp will deduce the language from the extension of the source file:
<code>.c</code>, <code>.cc</code>, <code>.m</code>, or <code>.S</code>.  Some other common
extensions for C++ and assembly are also recognized.  If cpp does not
recognize the extension, it will treat the file as C; this is the most
generic mode.

     <p><strong>Note:</strong> Previous versions of cpp accepted a <code>-lang</code> option
which selected both the language and the standards conformance level. 
This option has been removed, because it conflicts with the <code>-l</code>
option.

     <br><dt><code>-std=</code><var>standard</var><code></code>
     <dd><dt><code>-ansi</code>
     <dd>Specify the standard to which the code should conform.  Currently CPP
knows about C and C++ standards; others may be added in the future.

     <p><var>standard</var>
may be one of:
          <dl>
<dt><code>iso9899:1990</code>
          <dd><dt><code>c89</code>
          <dd>The ISO C standard from 1990.  <code>c89</code> is the customary shorthand for
this version of the standard.

          <p>The <code>-ansi</code> option is equivalent to <code>-std=c89</code>.

          <br><dt><code>iso9899:199409</code>
          <dd>The 1990 C standard, as amended in 1994.

          <br><dt><code>iso9899:1999</code>
          <dd><dt><code>c99</code>
          <dd><dt><code>iso9899:199x</code>
          <dd><dt><code>c9x</code>
          <dd>The revised ISO C standard, published in December 1999.  Before
publication, this was known as C9X.

          <br><dt><code>gnu89</code>
          <dd>The 1990 C standard plus GNU extensions.  This is the default.

          <br><dt><code>gnu99</code>
          <dd><dt><code>gnu9x</code>
          <dd>The 1999 C standard plus GNU extensions.

          <br><dt><code>c++98</code>
          <dd>The 1998 ISO C++ standard plus amendments.

          <br><dt><code>gnu++98</code>
          <dd>The same as <code>-std=c++98</code> plus GNU extensions.  This is the
default for C++ code. 
</dl>

     <br><dt><code>-I-</code>
     <dd>Split the include path.  Any directories specified with <code>-I</code>
options before <code>-I-</code> are searched only for headers requested with
<code>#include&nbsp;"</code><var>file</var><code>"</code>; they are not searched for
<code>#include&nbsp;&lt;</code><var>file</var><code>&gt;</code>.  If additional directories are
specified with <code>-I</code> options after the <code>-I-</code>, those
directories are searched for all <code>#include</code> directives.

     <p>In addition, <code>-I-</code> inhibits the use of the directory of the current
file directory as the first search directory for <code>#include&nbsp;"</code><var>file</var><code>"</code>.

     <br><dt><code>-nostdinc</code>
     <dd>Do not search the standard system directories for header files. 
Only the directories you have specified with <code>-I</code> options
(and the directory of the current file, if appropriate) are searched.

     <br><dt><code>-nostdinc++</code>
     <dd>Do not search for header files in the C++-specific standard directories,
but do still search the other standard directories.  (This option is
used when building the C++ library.)

     <br><dt><code>-include </code><var>file</var><code></code>
     <dd>Process <var>file</var> as if <code>#include "file"</code> appeared as the first
line of the primary source file.  However, the first directory searched
for <var>file</var> is the preprocessor's working directory <em>instead of</em>
the directory containing the main source file.  If not found there, it
is searched for in the remainder of the <code>#include "..."</code> search
chain as normal.

     <p>If multiple <code>-include</code> options are given, the files are included
in the order they appear on the command line.

     <br><dt><code>-imacros </code><var>file</var><code></code>
     <dd>Exactly like <code>-include</code>, except that any output produced by