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1 /**************************************************************************** |
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2 ** |
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3 ** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies). |
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4 ** All rights reserved. |
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37 ** |
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38 ** $QT_END_LICENSE$ |
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39 ** |
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40 ****************************************************************************/ |
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41 |
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42 /*! |
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43 \group string-processing |
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44 \title Classes for String Data |
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45 |
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46 \brief Classes for working with string data. |
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47 |
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48 These classes are relevant when working with string data. See the |
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49 \l{Unicode in Qt}{information about support for Unicode in Qt} for |
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50 more information. |
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51 */ |
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52 |
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53 |
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54 /*! |
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55 \page unicode.html |
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56 \title Unicode in Qt |
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57 \brief Information about support for Unicode in Qt. |
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58 |
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59 \keyword Unicode |
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60 |
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61 \ingroup frameworks-technologies |
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62 |
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63 Unicode is a multi-byte character set, portable across all major |
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64 computing platforms and with decent coverage over most of the world. |
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65 It is also single-locale; it includes no code pages or other |
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66 complexities that make software harder to write and test. There is no |
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67 competing character set that's reasonably cross-platform. For these |
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68 reasons, Unicode 4.0 is used as the native character set for Qt. |
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69 |
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70 \section1 Qt's Classes for Working with Strings |
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71 |
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72 These classes are relevant when working with string data. For information |
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73 about rendering text, see the \l{Rich Text Processing} overview, and if |
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74 your string data is in XML, see the \l{XML Processing} overview. |
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75 |
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76 \annotatedlist string-processing |
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77 |
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78 \section1 Information about Unicode on the Web |
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79 |
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80 The \l{http://www.unicode.org/}{Unicode Consortium} has a number |
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81 of documents available, including |
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82 |
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83 \list |
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84 |
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85 \i \l{http://www.unicode.org/unicode/standard/principles.html}{A |
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86 technical introduction to Unicode} |
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87 \i \l{http://www.unicode.org/unicode/standard/standard.html}{The |
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88 home page for the standard} |
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89 |
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90 \endlist |
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91 |
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92 |
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93 \section1 The Standard |
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94 |
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95 The current version of the standard is \l{http://www.unicode.org/versions/Unicode5.1.0/}{Unicode 5.1.0}. |
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96 |
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97 Previous printed versions of the specification: |
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98 |
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99 \list |
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100 \o \l{http://www.amazon.com/Unicode-Standard-Version-5-0-5th/dp/0321480910/trolltech/t}{The Unicode Standard, Version 5.0} |
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101 \o \l{http://www.amazon.com/exec/obidos/ASIN/0321185781/trolltech/t}{The Unicode Standard, version 4.0} |
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102 \o \l{http://www.amazon.com/exec/obidos/ASIN/0201616335/trolltech/t}{The Unicode Standard, version 3.2} |
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103 \o \l{http://www.amazon.com/exec/obidos/ASIN/0201473459/trolltech/t}{The Unicode Standard, version 2.0} \mdash |
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104 see also the \l{http://www.unicode.org/unicode/reports/tr8.html}{2.1 update} and |
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105 \l{http://www.unicode.org/unicode/standard/versions/enumeratedversions.html#Unicode 2.1.9}{the 2.1.9 data files} at |
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106 \l{http://www.unicode.org}. |
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107 \endlist |
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108 |
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109 \section1 Unicode in Qt |
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110 |
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111 In Qt, and in most applications that use Qt, most or all user-visible |
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112 strings are stored using Unicode. Qt provides: |
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113 |
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114 \list |
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115 |
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116 \i Translation to/from legacy encodings for file I/O: see |
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117 QTextCodec and QTextStream. |
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118 \i Translation from Input Methods and 8-bit keyboard input. |
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119 \i Translation to legacy character sets for on-screen display. |
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120 \i A string class, QString, that stores Unicode characters, with |
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121 support for migrating from C strings including fast (cached) |
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122 translation to and from US-ASCII, and all the usual string |
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123 operations. |
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124 \i Unicode-aware widgets where appropriate. |
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125 \i Unicode support detection on Windows, so that Qt provides Unicode |
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126 even on Windows platforms that do not support it natively. |
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127 |
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128 \endlist |
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129 |
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130 To fully benefit from Unicode, we recommend using QString for storing |
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131 all user-visible strings, and performing all text file I/O using |
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132 QTextStream. Use QKeyEvent::text() for keyboard input in any custom |
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133 widgets you write; it does not make much difference for slow typists |
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134 in Western Europe or North America, but for fast typists or people |
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135 using special input methods using text() is beneficial. |
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136 |
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137 All the function arguments in Qt that may be user-visible strings, |
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138 QLabel::setText() and a many others, take \c{const QString &}s. |
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139 QString provides implicit casting from \c{const char *} |
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140 so that things like |
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141 |
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142 \snippet doc/src/snippets/code/doc_src_unicode.qdoc 0 |
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143 |
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144 will work. There is also a function, QObject::tr(), that provides |
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145 translation support, like this: |
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146 |
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147 \snippet doc/src/snippets/code/doc_src_unicode.qdoc 1 |
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148 |
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149 QObject::tr() maps from \c{const char *} to a Unicode string, and |
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150 uses installable QTranslator objects to do the mapping. |
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151 |
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152 Qt provides a number of built-in QTextCodec classes, that is, |
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153 classes that know how to translate between Unicode and legacy |
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154 encodings to support programs that must talk to other programs or |
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155 read/write files in legacy file formats. |
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156 |
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157 By default, conversion to/from \c{const char *} uses a |
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158 locale-dependent codec. However, applications can easily find codecs |
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159 for other locales, and set any open file or network connection to use |
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160 a special codec. It is also possible to install new codecs, for |
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161 encodings that the built-in ones do not support. (At the time of |
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162 writing, Vietnamese/VISCII is one such example.) |
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163 |
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164 Since US-ASCII and ISO-8859-1 are so common, there are also especially |
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165 fast functions for mapping to and from them. For example, to open an |
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166 application's icon one might do this: |
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167 |
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168 \snippet doc/src/snippets/code/doc_src_unicode.qdoc 2 |
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169 |
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170 or |
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171 |
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172 \snippet doc/src/snippets/code/doc_src_unicode.qdoc 3 |
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173 |
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174 Regarding output, Qt will do a best-effort conversion from |
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175 Unicode to whatever encoding the system and fonts provide. |
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176 Depending on operating system, locale, font availability, and Qt's |
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177 support for the characters used, this conversion may be good or bad. |
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178 We will extend this in upcoming versions, with emphasis on the most |
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179 common locales first. |
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180 |
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181 \sa {Internationalization with Qt} |
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182 */ |