1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<!-- 4 == Copyright (c) 2001 Ronald Garcia 5 == 6 == Permission to use, copy, modify, distribute and sell this software 7 == and its documentation for any purpose is hereby granted without fee, 8 == provided that the above copyright notice appears in all copies and 9 == that both that copyright notice and this permission notice appear 10 == in supporting documentation. Ronald Garcia makes no 11 == representations about the suitability of this software for any 12 == purpose. It is provided "as is" without express or implied warranty. 13 --> 14<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 15<link rel="stylesheet" type="text/css" href="../../../boost.css"> 16<link rel="stylesheet" type="text/css" href="style.css"> 17<head> 18<title>UTF-8 Codecvt Facet</title> 19 20</head> 21 22<body bgcolor="#ffffff" link="#0000ee" text="#000000" 23 vlink="#551a8b" alink="#ff0000"> 24<img src="../../../boost.png" alt="C++ Boost" 25width="277" height="86"> <br clear="all"> 26 27 28<a name="sec:utf8-codecvt-facet-class"></a> 29 30 31<h1><code>utf8_codecvt_facet</code></h1> 32 33 34<pre> 35template< 36 typename InternType = wchar_t, 37 typename ExternType = char 38> utf8_codecvt_facet 39</pre> 40 41 42<h2>Rationale</h2> 43 44 45 UTF-8 is a method of encoding Unicode text in environments 46 where data is stored as 8-bit characters and some ascii characters 47 are considered special (i.e. Unix filesystem filenames) and tend 48 to appear more commonly than other characters. While 49 UTF-8 is convenient and efficient for storing data on filesystems, 50 it was not meant to be manipulated in memory by 51 applications. While some applications (such as Unix's 'cat') can 52 simply ignore the encoding of data, others should convert 53 from UTF-8 to UCS-4 (the more canonical representation of Unicode) 54 on reading from file, and reversing the process on writing out to 55 file. 56 57 <p>The C++ Standard IOStreams provides the <tt>std::codecvt</tt> 58 facet to handle specifically these cases. On reading from or 59 writing to a file, the <tt>std::basic_filebuf</tt> can call out to 60 the codecvt facet to convert data representations from external 61 format (ie. UTF-8) to internal format (ie. UCS-4) and 62 vice-versa. <tt>utf8_codecvt_facet</tt> is a specialization of 63 <tt>std::codecvt</tt> specifically designed to handle the case 64 of translating between UTF-8 and UCS-4. 65 66 67<h2>Template Parameters</h2> 68 69<table border summary="template parameters"> 70<tr> 71<th>Parameter</th><th>Description</th><th>Default</th> 72</tr> 73 74<tr> 75<td><tt>InternType</tt></td> 76<td>The internal type used to represent UCS-4 characters.</td> 77<td><tt>wchar_t</tt></td> 78</tr> 79 80<tr> 81<td><tt>ExternType</tt></td> 82<td>The external type used to represent UTF-8 octets.</td> 83<td><tt>char_t</tt></td> 84</tr> 85</table> 86 87 88<h2>Requirements</h2> 89 90 <tt>utf8_codecvt_facet</tt> defaults to using <tt>char</tt> as 91 its external data type and <tt>wchar_t</tt> as its internal 92 datatype, but on some architectures <tt>wchar_t</tt> is 93 not large enough to hold UCS-4 characters. In order to use 94 another internal type.You must also specialize <tt>std::codecvt</tt> 95 to handle your internal and external types. 96 (<tt>std::codecvt<char,wchar_t,std::mbstate_t></tt> is required to be 97 supplied by any standard-conforming compiler). 98 99 100<h2>Example Use</h2> 101 The following is a simple example of using this facet: 102 103<pre> 104 //... 105 // My encoding type 106 typedef wchar_t ucs4_t; 107 108 std::locale old_locale; 109 std::locale utf8_locale(old_locale,new utf8_codecvt_facet<ucs4_t>); 110 111 // Set a New global locale 112 std::locale::global(utf8_locale); 113 114 // Send the UCS-4 data out, converting to UTF-8 115 { 116 std::wofstream ofs("data.ucd"); 117 ofs.imbue(utf8_locale); 118 std::copy(ucs4_data.begin(),ucs4_data.end(), 119 std::ostream_iterator<ucs4_t,ucs4_t>(ofs)); 120 } 121 122 // Read the UTF-8 data back in, converting to UCS-4 on the way in 123 std::vector<ucs4_t> from_file; 124 { 125 std::wifstream ifs("data.ucd"); 126 ifs.imbue(utf8_locale); 127 ucs4_t item = 0; 128 while (ifs >> item) from_file.push_back(item); 129 } 130 //... 131</pre> 132 133 134<h2>History</h2> 135 136 This code was originally written as an iterator adaptor over 137 containers for use with UTF-8 encoded strings in memory. 138 Dietmar Kuehl suggested that it would be better provided as a 139 codecvt facet. 140 141<h2>Resources</h2> 142 143<ul> 144<li> <a href="http://www.unicode.org">Unicode Homepage</a> 145<li> <a href="http://home.CameloT.de/langer/iostreams.htm">Standard 146 C++ IOStreams and Locales</a> 147<li> <a href="http://www.research.att.com/~bs/3rd.html">The C++ 148 Programming Language Special Edition, Appendix D.</a> 149</ul> 150 151<br> 152<hr> 153<table summary="Copyright information"> 154<tr valign="top"> 155<td nowrap>Copyright © 2001</td> 156<td><a href="http://www.osl.iu.edu/~garcia">Ronald Garcia</a>, 157Indiana University 158(<a href="mailto:garcia@cs.indiana.edu">garcia@osl.iu.edu</a>)<br> 159<a href="http://www.osl.iu.edu/~lums">Andrew Lumsdaine</a>, 160Indiana University 161(<a href="mailto:lums@osl.iu.edu">lums@osl.iu.edu</a>)</td> 162</tr> 163</table> 164<p><i>© Copyright <a href="http://www.rrsd.com">Robert Ramey</a> 2002-2004. 165Distributed under the Boost Software License, Version 1.0. (See 166accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 167</i></p> 168</body> 169</html> 170 171 172
