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135 lines
7.2 KiB
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<title>Environment Variables - The C Preprocessor</title>
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any later version published by the Free Software Foundation. A copy of
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<a name="Environment-Variables"></a>
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Next: <a rel="next" accesskey="n" href="GNU-Free-Documentation-License.html#GNU-Free-Documentation-License">GNU Free Documentation License</a>,
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Previous: <a rel="previous" accesskey="p" href="Invocation.html#Invocation">Invocation</a>,
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Up: <a rel="up" accesskey="u" href="index.html#Top">Top</a>
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<h2 class="chapter">13 Environment Variables</h2>
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<p><a name="index-environment-variables-203"></a><!-- man begin ENVIRONMENT -->
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<p>This section describes the environment variables that affect how CPP
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operates. You can use them to specify directories or prefixes to use
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when searching for include files, or to control dependency output.
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<p>Note that you can also specify places to search using options such as
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<samp><span class="option">-I</span></samp>, and control dependency output with options like
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<samp><span class="option">-M</span></samp> (see <a href="Invocation.html#Invocation">Invocation</a>). These take precedence over
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environment variables, which in turn take precedence over the
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configuration of GCC.
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<!-- Copyright (C) 1999-2015 Free Software Foundation, Inc. -->
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<!-- This is part of the CPP and GCC manuals. -->
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<!-- For copying conditions, see the file gcc.texi. -->
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<!-- -->
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<!-- Environment variables affecting the preprocessor -->
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<!-- -->
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<!-- If this file is included with the flag ``cppmanual'' set, it is -->
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<!-- formatted for inclusion in the CPP manual; otherwise the main GCC manual. -->
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<dl>
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<dt><samp><span class="env">CPATH</span></samp><a name="index-CPATH-204"></a><dt><samp><span class="env">C_INCLUDE_PATH</span></samp><a name="index-C_005fINCLUDE_005fPATH-205"></a><dt><samp><span class="env">CPLUS_INCLUDE_PATH</span></samp><a name="index-CPLUS_005fINCLUDE_005fPATH-206"></a><dt><samp><span class="env">OBJC_INCLUDE_PATH</span></samp><a name="index-OBJC_005fINCLUDE_005fPATH-207"></a><dd><!-- Commented out until ObjC++ is part of GCC: -->
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<!-- @itemx OBJCPLUS_INCLUDE_PATH -->
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Each variable's value is a list of directories separated by a special
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character, much like <samp><span class="env">PATH</span></samp>, in which to look for header files.
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The special character, <code>PATH_SEPARATOR</code>, is target-dependent and
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determined at GCC build time. For Microsoft Windows-based targets it is a
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semicolon, and for almost all other targets it is a colon.
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<p><samp><span class="env">CPATH</span></samp> specifies a list of directories to be searched as if
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specified with <samp><span class="option">-I</span></samp>, but after any paths given with <samp><span class="option">-I</span></samp>
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options on the command line. This environment variable is used
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regardless of which language is being preprocessed.
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<p>The remaining environment variables apply only when preprocessing the
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particular language indicated. Each specifies a list of directories
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to be searched as if specified with <samp><span class="option">-isystem</span></samp>, but after any
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paths given with <samp><span class="option">-isystem</span></samp> options on the command line.
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<p>In all these variables, an empty element instructs the compiler to
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search its current working directory. Empty elements can appear at the
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beginning or end of a path. For instance, if the value of
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<samp><span class="env">CPATH</span></samp> is <code>:/special/include</code>, that has the same
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effect as ‘<samp><span class="samp">-I. -I/special/include<!-- /@w --></span></samp>’.
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<!-- man end -->
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<p>See also <a href="Search-Path.html#Search-Path">Search Path</a>.
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<!-- man begin ENVIRONMENT -->
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<br><dt><samp><span class="env">DEPENDENCIES_OUTPUT</span></samp><a name="index-DEPENDENCIES_005fOUTPUT-208"></a><dd><a name="index-dependencies-for-make-as-output-209"></a>If this variable is set, its value specifies how to output
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dependencies for Make based on the non-system header files processed
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by the compiler. System header files are ignored in the dependency
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output.
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<p>The value of <samp><span class="env">DEPENDENCIES_OUTPUT</span></samp> can be just a file name, in
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which case the Make rules are written to that file, guessing the target
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name from the source file name. Or the value can have the form
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‘<samp><var>file</var> <var>target</var></samp>’, in which case the rules are written to
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file <var>file</var> using <var>target</var> as the target name.
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<p>In other words, this environment variable is equivalent to combining
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the options <samp><span class="option">-MM</span></samp> and <samp><span class="option">-MF</span></samp>
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(see <a href="Invocation.html#Invocation">Invocation</a>),
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with an optional <samp><span class="option">-MT</span></samp> switch too.
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<br><dt><samp><span class="env">SUNPRO_DEPENDENCIES</span></samp><a name="index-SUNPRO_005fDEPENDENCIES-210"></a><dd><a name="index-dependencies-for-make-as-output-211"></a>This variable is the same as <samp><span class="env">DEPENDENCIES_OUTPUT</span></samp> (see above),
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except that system header files are not ignored, so it implies
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<samp><span class="option">-M</span></samp> rather than <samp><span class="option">-MM</span></samp>. However, the dependence on the
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main input file is omitted.
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See <a href="Invocation.html#Invocation">Invocation</a>.
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</dl>
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<!-- man end -->
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</body></html>
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