1<html lang="en"> 2<head> 3<title>Character sets - The C Preprocessor</title> 4<meta http-equiv="Content-Type" content="text/html"> 5<meta name="description" content="The C Preprocessor"> 6<meta name="generator" content="makeinfo 4.13"> 7<link title="Top" rel="start" href="index.html#Top"> 8<link rel="up" href="Overview.html#Overview" title="Overview"> 9<link rel="next" href="Initial-processing.html#Initial-processing" title="Initial processing"> 10<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> 11<!-- 12Copyright (C) 1987, 1989, 1991, 1992, 1993, 1994, 1995, 1996, 131997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 142008, 2009, 2010, 2011 15Free Software Foundation, Inc. 16 17Permission is granted to copy, distribute and/or modify this document 18under the terms of the GNU Free Documentation License, Version 1.3 or 19any later version published by the Free Software Foundation. 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The C standard discusses two character sets, but 63there are really at least four. 64 65 <p>The files input to CPP might be in any character set at all. CPP's 66very first action, before it even looks for line boundaries, is to 67convert the file into the character set it uses for internal 68processing. That set is what the C standard calls the <dfn>source</dfn> 69character set. It must be isomorphic with ISO 10646, also known as 70Unicode. CPP uses the UTF-8 encoding of Unicode. 71 72 <p>The character sets of the input files are specified using the 73<samp><span class="option">-finput-charset=</span></samp> option. 74 75 <p>All preprocessing work (the subject of the rest of this manual) is 76carried out in the source character set. If you request textual 77output from the preprocessor with the <samp><span class="option">-E</span></samp> option, it will be 78in UTF-8. 79 80 <p>After preprocessing is complete, string and character constants are 81converted again, into the <dfn>execution</dfn> character set. This 82character set is under control of the user; the default is UTF-8, 83matching the source character set. Wide string and character 84constants have their own character set, which is not called out 85specifically in the standard. Again, it is under control of the user. 86The default is UTF-16 or UTF-32, whichever fits in the target's 87<code>wchar_t</code> type, in the target machine's byte 88order.<a rel="footnote" href="#fn-1" name="fnd-1"><sup>1</sup></a> Octal and hexadecimal escape sequences do not undergo 89conversion; <tt>'\x12'</tt> has the value 0x12 regardless of the currently 90selected execution character set. All other escapes are replaced by 91the character in the source character set that they represent, then 92converted to the execution character set, just like unescaped 93characters. 94 95 <p>Unless the experimental <samp><span class="option">-fextended-identifiers</span></samp> option is used, 96GCC does not permit the use of characters outside the ASCII range, nor 97‘<samp><span class="samp">\u</span></samp>’ and ‘<samp><span class="samp">\U</span></samp>’ escapes, in identifiers. Even with that 98option, characters outside the ASCII range can only be specified with 99the ‘<samp><span class="samp">\u</span></samp>’ and ‘<samp><span class="samp">\U</span></samp>’ escapes, not used directly in identifiers. 100 101 <div class="footnote"> 102<hr> 103<h4>Footnotes</h4><p class="footnote"><small>[<a name="fn-1" href="#fnd-1">1</a>]</small> UTF-16 does not meet the requirements of the C 104standard for a wide character set, but the choice of 16-bit 105<code>wchar_t</code> is enshrined in some system ABIs so we cannot fix 106this.</p> 107 108 <hr></div> 109 110 </body></html> 111 112