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112 lines
4.9 KiB
HTML
112 lines
4.9 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>System Headers (The C Preprocessor)</title>
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<meta name="description" content="System Headers (The C Preprocessor)">
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<meta name="keywords" content="System Headers (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="Macros.html#Macros" rel="next" title="Macros">
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<link href="Wrapper-Headers.html#Wrapper-Headers" rel="prev" title="Wrapper Headers">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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blockquote.smallindentedblock {margin-right: 0em; 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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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.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="System-Headers"></a>
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<div class="header">
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<p>
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Previous: <a href="Wrapper-Headers.html#Wrapper-Headers" accesskey="p" rel="prev">Wrapper Headers</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="System-Headers-1"></a>
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<h3 class="section">2.8 System Headers</h3>
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<a name="index-system-header-files-1"></a>
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<p>The header files declaring interfaces to the operating system and
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runtime libraries often cannot be written in strictly conforming C.
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Therefore, GCC gives code found in <em>system headers</em> special
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treatment. All warnings, other than those generated by ‘<samp>#warning</samp>’
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(see <a href="Diagnostics.html#Diagnostics">Diagnostics</a>), are suppressed while GCC is processing a system
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header. Macros defined in a system header are immune to a few warnings
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wherever they are expanded. This immunity is granted on an ad-hoc
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basis, when we find that a warning generates lots of false positives
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because of code in macros defined in system headers.
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</p>
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<p>Normally, only the headers found in specific directories are considered
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system headers. These directories are determined when GCC is compiled.
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There are, however, two ways to make normal headers into system headers:
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</p>
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<ul>
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<li> Header files found in directories added to the search path with the
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<samp>-isystem</samp> and <samp>-idirafter</samp> command-line options are
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treated as system headers for the purposes of diagnostics.
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</li><li> <a name="index-_0023pragma-GCC-system_005fheader"></a>
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There is also a directive, <code>#pragma GCC <span class="nolinebreak">system_header</span><!-- /@w --></code>, which
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tells GCC to consider the rest of the current include file a system
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header, no matter where it was found. Code that comes before the
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‘<samp>#pragma</samp>’ in the file is not affected. <code>#pragma GCC <span class="nolinebreak">system_header</span><!-- /@w --></code> has no effect in the primary source file.
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</li></ul>
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</body>
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</html>
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