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Breadcrumbs go here --> <li>Writing Source Code for Translation</li> </ul> </div> <div class="toolbuttons toolblock"> <ul> <li id="smallA" class="t_button">A</li> <li id="medA" class="t_button active">A</li> <li id="bigA" class="t_button">A</li> <li id="print" class="t_button"><a href="javascript:this.print();"> <span>Print</span></a></li> </ul> </div> </div> <div class="content mainContent"> <link rel="prev" href="internationalization.html" /> <p class="naviNextPrevious headerNavi"> <a class="prevPage" href="internationalization.html">Internationalization with Qt</a> </p><p/> <div class="toc"> <h3><a name="toc">Contents</a></h3> <ul> <li class="level1"><a href="#the-basics">The Basics</a></li> <li class="level1"><a href="#defining-a-translation-context">Defining a Translation Context</a></li> <li class="level1"><a href="#using-tr-to-obtain-a-translation">Using tr() to Obtain a Translation</a></li> <li class="level1"><a href="#translator-comments">Translator Comments</a></li> <li class="level1"><a href="#adding-meta-data-to-strings">Adding Meta-Data to Strings</a></li> <li class="level1"><a href="#disambiguation">Disambiguation</a></li> <li class="level1"><a href="#character-encodings">Character Encodings</a></li> <li class="level1"><a href="#handling-plurals">Handling Plurals</a></li> <li class="level1"><a href="#enabling-translation">Enabling Translation</a></li> <li class="level1"><a href="#further-reading">Further Reading</a></li> </ul> </div> <h1 class="title">Writing Source Code for Translation</h1> <span class="subtitle"></span> <!-- $$$i18n-source-translation.html-description --> <div class="descr"> <a name="details"></a> <a name="the-basics"></a> <h2>The Basics</h2> <p>Developers use the <a href="qobject.html#tr">tr()</a> function to obtain translated text for their classes, typically for display purposes. This function is also used to indicate which text strings in an application are translatable.</p> <p>Qt indexes each translatable string by the <i>translation context</i> it is associated with; this is generally the name of the <a href="qobject.html">QObject</a> subclass it is used in.</p> <p>Translation contexts are defined for new <a href="qobject.html">QObject</a>-based classes by the use of the <a href="qobject.html#Q_OBJECT">Q_OBJECT</a> macro in each new class definition.</p> <p>When tr() is called, it looks up the translatable string using a <a href="qtranslator.html">QTranslator</a> object. For translation to work, one or more of these must have been installed on the application object in the way described in the <a href="#enabling-translation">Enabling Translation</a> section below.</p> <a name="defining-a-translation-context"></a> <h2>Defining a Translation Context</h2> <p>The translation context for <a href="qobject.html">QObject</a> and each <a href="qobject.html">QObject</a> subclass is the class name itself. Developers subclassing <a href="qobject.html">QObject</a> must use the <a href="qobject.html#Q_OBJECT">Q_OBJECT</a> macro in their class definition to override the translation context. This macro sets the context to the name of the subclass.</p> <p>For example, the following class definition includes the <a href="qobject.html#Q_OBJECT">Q_OBJECT</a> macro, implementing a new tr() that uses the <tt>MainWindow</tt> context:</p> <pre class="cpp"> <span class="keyword">class</span> MainWindow : <span class="keyword">public</span> <span class="type"><a href="qmainwindow.html">QMainWindow</a></span> { Q_OBJECT <span class="keyword">public</span>: MainWindow(); ...</pre> <p>If <a href="qobject.html#Q_OBJECT">Q_OBJECT</a> is not used in a class definition, the context will be inherited from the base class. For example, since all <a href="qobject.html">QObject</a>-based classes in Qt provide a context, a new <a href="qwidget.html">QWidget</a> subclass defined without a <a href="qobject.html#Q_OBJECT">Q_OBJECT</a> macro will use the <tt>QWidget</tt> context if its tr() function is invoked.</p> <a name="using-tr-to-obtain-a-translation"></a> <h2>Using tr() to Obtain a Translation</h2> <p>The following example shows how a translation is obtained for the class shown in the previous section:</p> <pre class="cpp"> <span class="type">void</span> MainWindow<span class="operator">::</span>createMenus() { fileMenu <span class="operator">=</span> menuBar()<span class="operator">-</span><span class="operator">></span>addMenu(tr(<span class="string">"&File"</span>)); ...</pre> <p>Here, the translation context is <tt>MainWindow</tt> because it is the <tt>MainWindow::tr()</tt> function that is invoked. The text returned by the tr() function is a translation of "&File" obtained from the <tt>MainWindow</tt> context.</p> <p>When Qt's translation tool, <a href="linguist-manager.html#lupdate">lupdate</a>, is used to process a set of source files, the text wrapped in tr() calls is stored in a section of the translation file that corresponds to its translation context.</p> <p>In some situations, it is useful to give a translation context explicitly by fully qualifying the call to tr(); for example:</p> <pre class="cpp"> <span class="type"><a href="qstring.html">QString</a></span> text <span class="operator">=</span> <span class="type"><a href="qscrollbar.html">QScrollBar</a></span><span class="operator">::</span>tr(<span class="string">"Page up"</span>);</pre> <p>This call obtains the translated text for "Page up" from the <tt>QScrollBar</tt> context. Developers can also use the <a href="qcoreapplication.html#translate">QCoreApplication::translate</a>() function to obtain a translation for a particular translation context.</p> <a name="translator-comments"></a> <h2>Translator Comments</h2> <p>Developers can include information about each translatable string to help translators with the translation process. These are extracted when <a href="linguist-manager.html#lupdate">lupdate</a> is used to process the source files. The recommended way to add comments is to annotate the tr() calls in your code with comments of the form:</p> <p><tt>//: ...</tt></p> <p>or</p> <p><tt><tt>/*</tt>: ... <tt>*/</tt></tt></p> <p>Examples:</p> <pre class="cpp"> <span class="comment">//: This name refers to a host name.</span> hostNameLabel<span class="operator">-</span><span class="operator">></span>setText(tr(<span class="string">"Name:"</span>)); <span class="comment">/*: This text refers to a C++ code example. */</span> <span class="type"><a href="qstring.html">QString</a></span> example <span class="operator">=</span> tr(<span class="string">"Example"</span>);</pre> <p>In these examples, the comments will be associated with the strings passed to tr() in the context of each call.</p> <a name="adding-meta-data-to-strings"></a> <h2>Adding Meta-Data to Strings</h2> <p>Additional data can be attached to each translatable message. These are extracted when <a href="linguist-manager.html#lupdate">lupdate</a> is used to process the source files. The recommended way to add meta-data is to annotate the tr() calls in your code with comments of the form:</p> <p><tt>//= <id></tt></p> <p>This can be used to give the message a unique identifier to support tools which need it.</p> <p>An alternative way to attach meta-data is to use the following syntax:</p> <p><tt>//~ <field name> <field contents></tt></p> <p>This can be used to attach meta-data to the message. The field name should consist of a domain prefix (possibly the conventional file extension of the file format the field is inspired by), a hyphen and the actual field name in underscore-delimited notation. For storage in TS files, the field name together with the prefix "extra-" will form an XML element name. The field contents will be XML-escaped, but otherwise appear verbatim as the element's contents. Any number of unique fields can be added to each message.</p> <p>Example:</p> <pre class="cpp"> <span class="comment">//: This is a comment for the translator.</span> <span class="comment">//= qtn_foo_bar</span> <span class="comment">//~ loc-layout_id foo_dialog</span> <span class="comment">//~ loc-blank False</span> <span class="comment">//~ magic-stuff This might mean something magic.</span> <span class="type"><a href="qstring.html">QString</a></span> text <span class="operator">=</span> MyMagicClass<span class="operator">::</span>tr(<span class="string">"Sim sala bim."</span>);</pre> <p>Meta-data appearing right in front of a magic TRANSLATOR comment applies to the whole TS file.</p> <a name="disambiguation"></a> <h2>Disambiguation</h2> <p>If the same translatable string is used in different roles within the same translation context, an additional identifying string may be passed in the call to <a href="qobject.html#tr">tr()</a>. This optional disambiguation argument is used to distinguish between otherwise identical strings.</p> <p>Example:</p> <pre class="cpp"> MyWindow<span class="operator">::</span>MyWindow() { <span class="type"><a href="qlabel.html">QLabel</a></span> <span class="operator">*</span>senderLabel <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qlabel.html">QLabel</a></span>(tr(<span class="string">"Name:"</span>)); <span class="type"><a href="qlabel.html">QLabel</a></span> <span class="operator">*</span>recipientLabel <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qlabel.html">QLabel</a></span>(tr(<span class="string">"Name:"</span><span class="operator">,</span> <span class="string">"recipient"</span>)); ...</pre> <p>In Qt 4.4 and earlier, this disambiguation parameter was the preferred way to specify comments to translators.</p> <a name="character-encodings"></a> <h2>Character Encodings</h2> <p>You can set the encoding for the source text by calling <a href="qtextcodec.html#setCodecForTr">QTextCodec::setCodecForTr</a>(). By default, the source text is assumed to be in Latin-1 encoding.</p> <a name="handling-plurals"></a> <h2>Handling Plurals</h2> <p>Some translatable strings contain placeholders for integer values and need to be translated differently depending on the values in use.</p> <p>To help with this problem, developers pass an additional integer argument to the <a href="qobject.html#tr">tr()</a> function, and typically use a special notation for plurals in each translatable string.</p> <p>If this argument is equal or greater than zero, all occurrences of <tt>%n</tt> in the resulting string are replaced with a decimal representation of the value supplied. In addition, the translation used will adapt to the value according to the rules for each language.</p> <p>Example:</p> <pre class="cpp"> <span class="type">int</span> n <span class="operator">=</span> messages<span class="operator">.</span>count(); showMessage(tr(<span class="string">"%n message(s) saved"</span><span class="operator">,</span> <span class="number">0</span><span class="operator">,</span> n));</pre> <p>The table below shows what string is returned depending on the active translation:</p> <table class="generic"> <thead><tr class="qt-style"><th ></th><th colspan="3">Active Translation</th></tr> <tr class="qt-style"><th ><i>n</i></th><th >No Translation</th><th >French</th><th >English</th></tr></thead> <tr valign="top" class="odd"><td >0</td><td >"0 message(s) saved"</td><td >"0 message sauvegardé"</td><td >"0 message<b>s</b> saved"</td></tr> <tr valign="top" class="even"><td >1</td><td >"1 message(s) saved"</td><td >"1 message sauvegardé"</td><td >"1 message saved"</td></tr> <tr valign="top" class="odd"><td >2</td><td >"2 message(s) saved"</td><td >"2 message<b>s</b> sauvegardé<b>s</b>"</td><td >"2 message<b>s</b> saved"</td></tr> <tr valign="top" class="even"><td >37</td><td >"37 message(s) saved"</td><td >"37 message<b>s</b> sauvegardé<b>s</b>"</td><td >"37 message<b>s</b> saved"</td></tr> </table> <p>This idiom is more flexible than the traditional approach; e.g.,</p> <pre class="cpp"> n <span class="operator">=</span><span class="operator">=</span> <span class="number">1</span> <span class="operator">?</span> tr(<span class="string">"%n message saved"</span>) : tr(<span class="string">"%n messages saved"</span>)</pre> <p>because it also works with target languages that have several plural forms (e.g., Irish has a special "dual" form that should be used when <tt>n</tt> is 2), and it handles the <i>n</i> == 0 case correctly for languages such as French that require the singular. See the <a href="linguist-manual.html">Qt Linguist Manual</a> for details.</p> <p>Instead of <tt>%n</tt>, you can use <tt>%Ln</tt> to produce a localized representation of <i>n</i>. The conversion uses the default locale, set using <a href="qlocale.html#setDefault">QLocale::setDefault</a>(). (If no default locale was specified, the "C" locale is used.)</p> <p>A summary of supported languages and the rules used to translate strings containing plurals can be obtained by running <tt>lupdate -list-languages</tt>.</p> <a name="enabling-translation"></a> <h2>Enabling Translation</h2> <p>Typically, your application's <tt>main()</tt> function will look like this:</p> <pre class="cpp"> <span class="type">int</span> main(<span class="type">int</span> argc<span class="operator">,</span> <span class="type">char</span> <span class="operator">*</span>argv<span class="operator">[</span><span class="operator">]</span>) { <span class="type"><a href="qapplication.html">QApplication</a></span> app(argc<span class="operator">,</span> argv); <span class="type"><a href="qtranslator.html">QTranslator</a></span> qtTranslator; qtTranslator<span class="operator">.</span>load(<span class="string">"qt_"</span> <span class="operator">+</span> <span class="type"><a href="qlocale.html">QLocale</a></span><span class="operator">::</span>system()<span class="operator">.</span>name()<span class="operator">,</span> <span class="type"><a href="qlibraryinfo.html">QLibraryInfo</a></span><span class="operator">::</span>location(<span class="type"><a href="qlibraryinfo.html">QLibraryInfo</a></span><span class="operator">::</span>TranslationsPath)); app<span class="operator">.</span>installTranslator(<span class="operator">&</span>qtTranslator); <span class="type"><a href="qtranslator.html">QTranslator</a></span> myappTranslator; myappTranslator<span class="operator">.</span>load(<span class="string">"myapp_"</span> <span class="operator">+</span> <span class="type"><a href="qlocale.html">QLocale</a></span><span class="operator">::</span>system()<span class="operator">.</span>name()); app<span class="operator">.</span>installTranslator(<span class="operator">&</span>myappTranslator); <span class="operator">.</span><span class="operator">.</span><span class="operator">.</span> <span class="keyword">return</span> app<span class="operator">.</span>exec(); }</pre> <p>Note the use of <a href="qlibraryinfo.html#location">QLibraryInfo::location</a>() to locate the Qt translations. Developers should request the path to the translations at run-time by passing <a href="qlibraryinfo.html#LibraryLocation-enum">QLibraryInfo::TranslationsPath</a> to this function instead of using the <tt>QTDIR</tt> environment variable in their applications.</p> <a name="further-reading"></a> <h2>Further Reading</h2> <p><a href="linguist-manual.html">Qt Linguist Manual</a>, <a href="linguist-hellotr.html">Hello tr</a>() Example</p> </div> <!-- @@@i18n-source-translation.html --> <p class="naviNextPrevious footerNavi"> <a class="prevPage" href="internationalization.html">Internationalization with Qt</a> </p> </div> </div> </div> <div class="ft"> <span></span> </div> </div> <div class="footer"> <p> <acronym title="Copyright">©</acronym> 2015 The Qt Company Ltd. 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