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195 lines
8.5 KiB
HTML
195 lines
8.5 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1987-2018 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation. A copy of
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the license is included in the
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section entitled "GNU Free Documentation License".
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This manual contains no Invariant Sections. The Front-Cover Texts are
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(a) (see below), and the Back-Cover Texts are (b) (see below).
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Environment Variables (The C Preprocessor)</title>
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<meta name="description" content="Environment Variables (The C Preprocessor)">
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<meta name="keywords" content="Environment Variables (The C Preprocessor)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Index-of-Directives.html#Index-of-Directives" rel="index" title="Index of Directives">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="index.html#Top" rel="up" title="Top">
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<link href="GNU-Free-Documentation-License.html#GNU-Free-Documentation-License" rel="next" title="GNU Free Documentation License">
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<link href="Invocation.html#Invocation" rel="prev" title="Invocation">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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div.example {margin-left: 3.2em}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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span.sansserif {font-family: sans-serif; font-weight: normal}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Environment-Variables"></a>
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<div class="header">
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<p>
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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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</div>
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<hr>
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<a name="Environment-Variables-1"></a>
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<h2 class="chapter">13 Environment Variables</h2>
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<a name="index-environment-variables"></a>
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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>
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<p>Note that you can also specify places to search using options such as
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<samp>-I</samp>, and control dependency output with options like
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<samp>-M</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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</p>
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<dl compact="compact">
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<dt><code>CPATH</code>
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<a name="index-CPATH"></a>
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</dt>
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<dt><code>C_INCLUDE_PATH</code>
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<a name="index-C_005fINCLUDE_005fPATH"></a>
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</dt>
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<dt><code>CPLUS_INCLUDE_PATH</code>
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<a name="index-CPLUS_005fINCLUDE_005fPATH"></a>
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</dt>
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<dt><code>OBJC_INCLUDE_PATH</code>
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<a name="index-OBJC_005fINCLUDE_005fPATH"></a>
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</dt>
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<dd><p>Each variable’s value is a list of directories separated by a special
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character, much like <code>PATH</code>, 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>
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<p><code>CPATH</code> specifies a list of directories to be searched as if
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specified with <samp>-I</samp>, but after any paths given with <samp>-I</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>
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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>-isystem</samp>, but after any
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paths given with <samp>-isystem</samp> options on the command line.
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</p>
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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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<code>CPATH</code> is <code>:/special/include</code>, that has the same
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effect as ‘<samp><span class="nolinebreak">-I.</span> <span class="nolinebreak">-I/special/include</span><!-- /@w --></samp>’.
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</p>
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<p>See also <a href="Search-Path.html#Search-Path">Search Path</a>.
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</p>
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</dd>
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<dt><code>DEPENDENCIES_OUTPUT</code>
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<a name="index-DEPENDENCIES_005fOUTPUT"></a>
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</dt>
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<dd><a name="index-dependencies-for-make-as-output"></a>
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<p>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>
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<p>The value of <code>DEPENDENCIES_OUTPUT</code> 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>
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<p>In other words, this environment variable is equivalent to combining
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the options <samp>-MM</samp> and <samp>-MF</samp>
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(see <a href="Invocation.html#Invocation">Invocation</a>),
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with an optional <samp>-MT</samp> switch too.
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</p>
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</dd>
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<dt><code>SUNPRO_DEPENDENCIES</code>
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<a name="index-SUNPRO_005fDEPENDENCIES"></a>
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</dt>
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<dd><a name="index-dependencies-for-make-as-output-1"></a>
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<p>This variable is the same as <code>DEPENDENCIES_OUTPUT</code> (see above),
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except that system header files are not ignored, so it implies
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<samp>-M</samp> rather than <samp>-MM</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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</p>
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</dd>
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<dt><code>SOURCE_DATE_EPOCH</code>
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<a name="index-SOURCE_005fDATE_005fEPOCH"></a>
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</dt>
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<dd><p>If this variable is set, its value specifies a UNIX timestamp to be
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used in replacement of the current date and time in the <code>__DATE__</code>
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and <code>__TIME__</code> macros, so that the embedded timestamps become
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reproducible.
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</p>
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<p>The value of <code>SOURCE_DATE_EPOCH</code> must be a UNIX timestamp,
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defined as the number of seconds (excluding leap seconds) since
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01 Jan 1970 00:00:00 represented in ASCII; identical to the output of
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‘<samp><code>date +%s</code></samp>’ on GNU/Linux and other systems that support the
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<code>%s</code> extension in the <code>date</code> command.
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</p>
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<p>The value should be a known timestamp such as the last modification
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time of the source or package and it should be set by the build
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process.
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</p>
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</dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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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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</div>
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</body>
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</html>
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