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148 lines
5.8 KiB
HTML
148 lines
5.8 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>Include Operation (The C Preprocessor)</title>
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<meta name="description" content="Include Operation (The C Preprocessor)">
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<meta name="keywords" content="Include Operation (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="Search-Path.html#Search-Path" rel="next" title="Search Path">
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<link href="Include-Syntax.html#Include-Syntax" rel="prev" title="Include Syntax">
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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="Include-Operation"></a>
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<div class="header">
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<p>
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Next: <a href="Search-Path.html#Search-Path" accesskey="n" rel="next">Search Path</a>, Previous: <a href="Include-Syntax.html#Include-Syntax" accesskey="p" rel="prev">Include Syntax</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="Include-Operation-1"></a>
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<h3 class="section">2.2 Include Operation</h3>
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<p>The ‘<samp>#include</samp>’ directive works by directing the C preprocessor to
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scan the specified file as input before continuing with the rest of the
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current file. The output from the preprocessor contains the output
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already generated, followed by the output resulting from the included
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file, followed by the output that comes from the text after the
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‘<samp>#include</samp>’ directive. For example, if you have a header file
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<samp>header.h</samp> as follows,
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</p>
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<div class="smallexample">
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<pre class="smallexample">char *test (void);
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</pre></div>
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<p>and a main program called <samp>program.c</samp> that uses the header file,
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like this,
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</p>
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<div class="smallexample">
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<pre class="smallexample">int x;
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#include "header.h"
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int
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main (void)
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{
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puts (test ());
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}
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</pre></div>
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<p>the compiler will see the same token stream as it would if
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<samp>program.c</samp> read
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</p>
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<div class="smallexample">
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<pre class="smallexample">int x;
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char *test (void);
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int
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main (void)
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{
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puts (test ());
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}
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</pre></div>
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<p>Included files are not limited to declarations and macro definitions;
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those are merely the typical uses. Any fragment of a C program can be
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included from another file. The include file could even contain the
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beginning of a statement that is concluded in the containing file, or
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the end of a statement that was started in the including file. However,
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an included file must consist of complete tokens. Comments and string
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literals which have not been closed by the end of an included file are
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invalid. For error recovery, they are considered to end at the end of
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the file.
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</p>
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<p>To avoid confusion, it is best if header files contain only complete
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syntactic units—function declarations or definitions, type
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declarations, etc.
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</p>
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<p>The line following the ‘<samp>#include</samp>’ directive is always treated as a
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separate line by the C preprocessor, even if the included file lacks a
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final newline.
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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="Search-Path.html#Search-Path" accesskey="n" rel="next">Search Path</a>, Previous: <a href="Include-Syntax.html#Include-Syntax" accesskey="p" rel="prev">Include Syntax</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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