141 lines
6.2 KiB
HTML
141 lines
6.2 KiB
HTML
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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) 1987-2016 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 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>The C Preprocessor: Character sets</title>
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<meta name="description" content="The C Preprocessor: Character sets">
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<meta name="keywords" content="The C Preprocessor: Character sets">
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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="Overview.html#Overview" rel="up" title="Overview">
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<link href="Initial-processing.html#Initial-processing" rel="next" title="Initial processing">
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<link href="Overview.html#Overview" rel="prev" title="Overview">
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<style type="text/css">
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-->
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</style>
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</head>
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="Character-sets"></a>
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<div class="header">
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<p>
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Next: <a href="Initial-processing.html#Initial-processing" accesskey="n" rel="next">Initial processing</a>, Up: <a href="Overview.html#Overview" accesskey="u" rel="up">Overview</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="Character-sets-1"></a>
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<h3 class="section">1.1 Character sets</h3>
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<p>Source code character set processing in C and related languages is
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rather complicated. The C standard discusses two character sets, but
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there are really at least four.
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</p>
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<p>The files input to CPP might be in any character set at all. CPP’s
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very first action, before it even looks for line boundaries, is to
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convert the file into the character set it uses for internal
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processing. That set is what the C standard calls the <em>source</em>
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character set. It must be isomorphic with ISO 10646, also known as
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Unicode. CPP uses the UTF-8 encoding of Unicode.
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</p>
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<p>The character sets of the input files are specified using the
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<samp>-finput-charset=</samp> option.
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</p>
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<p>All preprocessing work (the subject of the rest of this manual) is
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carried out in the source character set. If you request textual
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output from the preprocessor with the <samp>-E</samp> option, it will be
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in UTF-8.
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</p>
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<p>After preprocessing is complete, string and character constants are
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converted again, into the <em>execution</em> character set. This
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character set is under control of the user; the default is UTF-8,
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matching the source character set. Wide string and character
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constants have their own character set, which is not called out
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specifically in the standard. Again, it is under control of the user.
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The default is UTF-16 or UTF-32, whichever fits in the target’s
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<code>wchar_t</code> type, in the target machine’s byte
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order.<a name="DOCF1" href="#FOOT1"><sup>1</sup></a> Octal and hexadecimal escape sequences do not undergo
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conversion; <tt>'\x12'</tt> has the value 0x12 regardless of the currently
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selected execution character set. All other escapes are replaced by
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the character in the source character set that they represent, then
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converted to the execution character set, just like unescaped
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characters.
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</p>
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<p>In identifiers, characters outside the ASCII range can only be
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specified with the ‘<samp>\u</samp>’ and ‘<samp>\U</samp>’ escapes, not used
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directly. If strict ISO C90 conformance is specified with an option
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such as <samp>-std=c90</samp>, or <samp>-fno-extended-identifiers</samp> is
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used, then those escapes are not permitted in identifiers.
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</p>
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<div class="footnote">
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<hr>
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<h4 class="footnotes-heading">Footnotes</h4>
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<h3><a name="FOOT1" href="#DOCF1">(1)</a></h3>
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<p>UTF-16 does not meet the requirements of the C
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standard for a wide character set, but the choice of 16-bit
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<code>wchar_t</code> is enshrined in some system ABIs so we cannot fix
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this.</p>
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</div>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Initial-processing.html#Initial-processing" accesskey="n" rel="next">Initial processing</a>, Up: <a href="Overview.html#Overview" accesskey="u" rel="up">Overview</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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