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| <title>The C Preprocessor: Environment Variables</title> |
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| <a name="Environment-Variables"></a> |
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| Next: <a href="GNU-Free-Documentation-License.html#GNU-Free-Documentation-License" accesskey="n" rel="next">GNU Free Documentation License</a>, Previous: <a href="Invocation.html#Invocation" accesskey="p" rel="prev">Invocation</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Index-of-Directives.html#Index-of-Directives" title="Index" rel="index">Index</a>]</p> |
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| <a name="Environment-Variables-1"></a> |
| <h2 class="chapter">13 Environment Variables</h2> |
| <a name="index-environment-variables"></a> |
| |
| <p>This section describes the environment variables that affect how CPP |
| operates. You can use them to specify directories or prefixes to use |
| when searching for include files, or to control dependency output. |
| </p> |
| <p>Note that you can also specify places to search using options such as |
| <samp>-I</samp>, and control dependency output with options like |
| <samp>-M</samp> (see <a href="Invocation.html#Invocation">Invocation</a>). These take precedence over |
| environment variables, which in turn take precedence over the |
| configuration of GCC. |
| </p> |
| |
| |
| |
| <dl compact="compact"> |
| <dt><code>CPATH</code> |
| <a name="index-CPATH"></a> |
| </dt> |
| <dt><code>C_INCLUDE_PATH</code> |
| <a name="index-C_005fINCLUDE_005fPATH"></a> |
| </dt> |
| <dt><code>CPLUS_INCLUDE_PATH</code> |
| <a name="index-CPLUS_005fINCLUDE_005fPATH"></a> |
| </dt> |
| <dt><code>OBJC_INCLUDE_PATH</code> |
| <a name="index-OBJC_005fINCLUDE_005fPATH"></a> |
| </dt> |
| <dd><p>Each variable’s value is a list of directories separated by a special |
| character, much like <code>PATH</code>, in which to look for header files. |
| The special character, <code>PATH_SEPARATOR</code>, is target-dependent and |
| determined at GCC build time. For Microsoft Windows-based targets it is a |
| semicolon, and for almost all other targets it is a colon. |
| </p> |
| <p><code>CPATH</code> specifies a list of directories to be searched as if |
| specified with <samp>-I</samp>, but after any paths given with <samp>-I</samp> |
| options on the command line. This environment variable is used |
| regardless of which language is being preprocessed. |
| </p> |
| <p>The remaining environment variables apply only when preprocessing the |
| particular language indicated. Each specifies a list of directories |
| to be searched as if specified with <samp>-isystem</samp>, but after any |
| paths given with <samp>-isystem</samp> options on the command line. |
| </p> |
| <p>In all these variables, an empty element instructs the compiler to |
| search its current working directory. Empty elements can appear at the |
| beginning or end of a path. For instance, if the value of |
| <code>CPATH</code> is <code>:/special/include</code>, that has the same |
| effect as ‘<samp><span class="nolinebreak">-I.</span> <span class="nolinebreak">-I/special/include</span><!-- /@w --></samp>’. |
| </p> |
| <p>See also <a href="Search-Path.html#Search-Path">Search Path</a>. |
| </p> |
| </dd> |
| <dt><code>DEPENDENCIES_OUTPUT</code> |
| <a name="index-DEPENDENCIES_005fOUTPUT"></a> |
| </dt> |
| <dd><a name="index-dependencies-for-make-as-output"></a> |
| <p>If this variable is set, its value specifies how to output |
| dependencies for Make based on the non-system header files processed |
| by the compiler. System header files are ignored in the dependency |
| output. |
| </p> |
| <p>The value of <code>DEPENDENCIES_OUTPUT</code> can be just a file name, in |
| which case the Make rules are written to that file, guessing the target |
| name from the source file name. Or the value can have the form |
| ‘<samp><var>file</var> <var>target</var></samp>’, in which case the rules are written to |
| file <var>file</var> using <var>target</var> as the target name. |
| </p> |
| <p>In other words, this environment variable is equivalent to combining |
| the options <samp>-MM</samp> and <samp>-MF</samp> |
| (see <a href="Invocation.html#Invocation">Invocation</a>), |
| with an optional <samp>-MT</samp> switch too. |
| </p> |
| </dd> |
| <dt><code>SUNPRO_DEPENDENCIES</code> |
| <a name="index-SUNPRO_005fDEPENDENCIES"></a> |
| </dt> |
| <dd><a name="index-dependencies-for-make-as-output-1"></a> |
| <p>This variable is the same as <code>DEPENDENCIES_OUTPUT</code> (see above), |
| except that system header files are not ignored, so it implies |
| <samp>-M</samp> rather than <samp>-MM</samp>. However, the dependence on the |
| main input file is omitted. |
| See <a href="Invocation.html#Invocation">Invocation</a>. |
| </p></dd> |
| </dl> |
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