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| <h2 class="chapter">13 Environment Variables</h2> |
| |
| <p><a name="index-environment-variables-198"></a><!-- man begin ENVIRONMENT --> |
| |
| <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>Note that you can also specify places to search using options such as |
| <samp><span class="option">-I</span></samp>, and control dependency output with options like |
| <samp><span class="option">-M</span></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. |
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| <dl> |
| <dt><samp><span class="env">CPATH</span></samp><a name="index-CPATH-199"></a><dt><samp><span class="env">C_INCLUDE_PATH</span></samp><a name="index-C_005fINCLUDE_005fPATH-200"></a><dt><samp><span class="env">CPLUS_INCLUDE_PATH</span></samp><a name="index-CPLUS_005fINCLUDE_005fPATH-201"></a><dt><samp><span class="env">OBJC_INCLUDE_PATH</span></samp><a name="index-OBJC_005fINCLUDE_005fPATH-202"></a><dd><!-- Commented out until ObjC++ is part of GCC: --> |
| <!-- @itemx OBJCPLUS_INCLUDE_PATH --> |
| Each variable's value is a list of directories separated by a special |
| character, much like <samp><span class="env">PATH</span></samp>, 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><samp><span class="env">CPATH</span></samp> specifies a list of directories to be searched as if |
| specified with <samp><span class="option">-I</span></samp>, but after any paths given with <samp><span class="option">-I</span></samp> |
| options on the command line. This environment variable is used |
| regardless of which language is being preprocessed. |
| |
| <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><span class="option">-isystem</span></samp>, but after any |
| paths given with <samp><span class="option">-isystem</span></samp> options on the command line. |
| |
| <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 |
| <samp><span class="env">CPATH</span></samp> is <code>:/special/include</code>, that has the same |
| effect as ‘<samp><span class="samp">-I. -I/special/include<!-- /@w --></span></samp>’. |
| |
| <!-- man end --> |
| <p>See also <a href="Search-Path.html#Search-Path">Search Path</a>. |
| <!-- man begin ENVIRONMENT --> |
| |
| <br><dt><samp><span class="env">DEPENDENCIES_OUTPUT</span></samp><a name="index-DEPENDENCIES_005fOUTPUT-203"></a><dd><a name="index-dependencies-for-make-as-output-204"></a>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>The value of <samp><span class="env">DEPENDENCIES_OUTPUT</span></samp> 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>In other words, this environment variable is equivalent to combining |
| the options <samp><span class="option">-MM</span></samp> and <samp><span class="option">-MF</span></samp> |
| (see <a href="Invocation.html#Invocation">Invocation</a>), |
| with an optional <samp><span class="option">-MT</span></samp> switch too. |
| |
| <br><dt><samp><span class="env">SUNPRO_DEPENDENCIES</span></samp><a name="index-SUNPRO_005fDEPENDENCIES-205"></a><dd><a name="index-dependencies-for-make-as-output-206"></a>This variable is the same as <samp><span class="env">DEPENDENCIES_OUTPUT</span></samp> (see above), |
| except that system header files are not ignored, so it implies |
| <samp><span class="option">-M</span></samp> rather than <samp><span class="option">-MM</span></samp>. However, the dependence on the |
| main input file is omitted. |
| See <a href="Invocation.html#Invocation">Invocation</a>. |
| </dl> |
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