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134 lines
6.4 KiB
HTML
134 lines
6.4 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>Search Path (The C Preprocessor)</title>
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<meta name="description" content="Search Path (The C Preprocessor)">
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<meta name="keywords" content="Search Path (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="Header-Files.html#Header-Files" rel="up" title="Header Files">
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<link href="Once_002dOnly-Headers.html#Once_002dOnly-Headers" rel="next" title="Once-Only Headers">
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<link href="Include-Operation.html#Include-Operation" rel="prev" title="Include Operation">
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<style type="text/css">
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<!--
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a.summary-letter {text-decoration: none}
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blockquote.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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blockquote.smallquotation {font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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div.smallexample {margin-left: 3.2em}
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div.smalllisp {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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pre.menu-preformatted {font-family: serif}
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pre.smalldisplay {font-family: inherit; font-size: smaller}
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pre.smallexample {font-size: smaller}
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pre.smallformat {font-family: inherit; font-size: smaller}
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pre.smalllisp {font-size: smaller}
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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="Search-Path"></a>
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<div class="header">
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<p>
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Next: <a href="Once_002dOnly-Headers.html#Once_002dOnly-Headers" accesskey="n" rel="next">Once-Only Headers</a>, Previous: <a href="Include-Operation.html#Include-Operation" accesskey="p" rel="prev">Include Operation</a>, Up: <a href="Header-Files.html#Header-Files" accesskey="u" rel="up">Header Files</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="Search-Path-1"></a>
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<h3 class="section">2.3 Search Path</h3>
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<p>By default, the preprocessor looks for header files included by the quote
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form of the directive <code>#include "<var>file</var>"<!-- /@w --></code> first relative to
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the directory of the current file, and then in a preconfigured list
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of standard system directories.
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For example, if <samp>/usr/include/sys/stat.h</samp> contains
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<code>#include "types.h"<!-- /@w --></code>, GCC looks for <samp>types.h</samp> first in
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<samp>/usr/include/sys</samp>, then in its usual search path.
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</p>
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<p>For the angle-bracket form <code>#include <<var>file</var>><!-- /@w --></code>, the
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preprocessor’s default behavior is to look only in the standard system
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directories. The exact search directory list depends on the target
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system, how GCC is configured, and where it is installed. You can
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find the default search directory list for your version of CPP by
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invoking it with the <samp>-v</samp> option. For example,
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</p>
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<div class="smallexample">
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<pre class="smallexample">cpp -v /dev/null -o /dev/null
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</pre></div>
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<p>There are a number of command-line options you can use to add
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additional directories to the search path.
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The most commonly-used option is <samp>-I<var>dir</var></samp>, which causes
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<var>dir</var> to be searched after the current directory (for the quote
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form of the directive) and ahead of the standard system directories.
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You can specify multiple <samp>-I</samp> options on the command line,
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in which case the directories are searched in left-to-right order.
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</p>
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<p>If you need separate control over the search paths for the quote and
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angle-bracket forms of the ‘<samp>#include</samp>’ directive, you can use the
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<samp>-iquote</samp> and/or <samp>-isystem</samp> options instead of <samp>-I</samp>.
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See <a href="Invocation.html#Invocation">Invocation</a>, for a detailed description of these options, as
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well as others that are less generally useful.
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</p>
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<p>If you specify other options on the command line, such as <samp>-I</samp>,
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that affect where the preprocessor searches for header files, the
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directory list printed by the <samp>-v</samp> option reflects the actual
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search path used by the preprocessor.
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</p>
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<p>Note that you can also prevent the preprocessor from searching any of
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the default system header directories with the <samp>-nostdinc</samp>
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option. This is useful when you are compiling an operating system
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kernel or some other program that does not use the standard C library
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facilities, or the standard C library itself.
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Once_002dOnly-Headers.html#Once_002dOnly-Headers" accesskey="n" rel="next">Once-Only Headers</a>, Previous: <a href="Include-Operation.html#Include-Operation" accesskey="p" rel="prev">Include Operation</a>, Up: <a href="Header-Files.html#Header-Files" accesskey="u" rel="up">Header Files</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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