<?xml version="1.0" encoding="iso-8859-1"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <!-- /tmp/qt-4.3.4-qt-1203442408707/qt-x11-opensource-src-4.3.4/doc/src/resources.qdoc --> <head> <title>Qt 4.3: The Qt Resource System</title> <link href="classic.css" rel="stylesheet" type="text/css" /> </head> <body> <table border="0" cellpadding="0" cellspacing="0" width="100%"> <tr> <td align="left" valign="top" width="32"><a href="http://www.trolltech.com/products/qt"><img src="images/qt-logo.png" align="left" width="32" height="32" border="0" /></a></td> <td width="1"> </td><td class="postheader" valign="center"><a href="index.html"><font color="#004faf">Home</font></a> · <a href="classes.html"><font color="#004faf">All Classes</font></a> · <a href="mainclasses.html"><font color="#004faf">Main Classes</font></a> · <a href="groups.html"><font color="#004faf">Grouped Classes</font></a> · <a href="modules.html"><font color="#004faf">Modules</font></a> · <a href="functions.html"><font color="#004faf">Functions</font></a></td> <td align="right" valign="top" width="230"><a href="http://www.trolltech.com"><img src="images/trolltech-logo.png" align="right" width="203" height="32" border="0" /></a></td></tr></table><h1 align="center">The Qt Resource System<br /><small></small></h1> <a name="resource-system"></a><p>The Qt resource system is a platform-independent mechanism for storing binary files in the application's executable. This is useful if your application always needs a certain set of files (icons, translation files, etc.) and you don't want to run the risk of losing the files.</p> <p>The resource system is based on tight cooperation between <a href="qmake-manual.html#qmake">qmake</a>, <a href="rcc.html#rcc">rcc</a> (Qt's resource compiler), and <a href="qfile.html">QFile</a>. It obsoletes Qt 3's <tt>qembed</tt> tool and the <a href="http://doc.trolltech.com/qq/qq05-iconography.html#imagestorage">image collection</a> mechanism.</p> <a name="resource-collection-files"></a> <h2>Resource Collection Files (<tt>.qrc</tt>)</h2> <p>The resources associated with an application are specified in a <tt>.qrc</tt> file, an XML-based file format that lists files on the disk and optionally assigns them a resource name that the application must use to access the resource.</p> <p>Here's an example <tt>.qrc</tt> file:</p> <pre> <!DOCTYPE RCC><RCC version="1.0"> <qresource> <file>images/copy.png</file> <file>images/cut.png</file> <file>images/new.png</file> <file>images/open.png</file> <file>images/paste.png</file> <file>images/save.png</file> </qresource> </RCC></pre> <p>The resource files listed in the <tt>.qrc</tt> file are files that are part of the application's source tree. The specified paths are relative to the directory containing the <tt>.qrc</tt> file. Note that the listed resource files must be located in the same directory as the <tt>.qrc</tt> file, or one of its subdirectories.</p> <p>Resource data can either be compiled into the binary and thus accessed immediately in application code, or a binary resource can be created and at a later point in application code registered with the resource system.</p> <p>By default, resources are accessible in the application under the same name as they have in the source tree, with a <tt>:/</tt> prefix. For example, the path <tt>:/images/cut.png</tt> would give access to the <tt>cut.png</tt> file, whose location in the application's source tree is <tt>images/cut.png</tt>. This can be changed using the <tt>file</tt> tag's <tt>alias</tt> attribute:</p> <pre> <file alias="cut-img.png">images/cut.png</file></pre> <p>The file is then accessible as <tt>:/cut-img.png</tt> from the application. It is also possible to specify a path prefix for all files in the <tt>.qrc</tt> file using the <tt>qresource</tt> tag's <tt>prefix</tt> attribute:</p> <pre> <qresource prefix="/myresources"> <file alias="cut-img.png">images/cut.png</file> </qresource></pre> <p>In this case, the file is accessible as <tt>:/myresources/cut-img.png</tt>.</p> <p>Some resources, such as translation files and icons, many need to change based on the user's locale. This is done by adding a <tt>lang</tt> attribute to the <tt>qresource</tt> tag, specifying a suitable locale string. For example:</p> <pre> <qresource> <file>cut.jpg</file> </qresource> <qresource lang="fr"> <file alias="cut.jpg">cut_fr.jpg</file> </qresource></pre> <p>If the user's locale is French (i.e., <a href="qlocale.html#system">QLocale::system</a>().name() returns "fr_FR"), <tt>:/cut.jpg</tt> becomes a reference to the <tt>cut_fr.jpg</tt> image. For other locales, <tt>cut.jpg</tt> is used.</p> <p>See the <a href="qlocale.html">QLocale</a> documentation for a description of the format to use for locale strings.</p> <a name="external-binary-resources"></a> <h3>External Binary Resources</h3> <p>For an external binary resource to be created you must create the resource data (commonly given the <tt>.rcc</tt> extension) by passing the -binary switch to <a href="rcc.html#rcc">rcc</a>. Once the binary resource is created you can register the resource with the <a href="qresource.html">QResource</a> API.</p> <p>For example, a set of resource data specified in a <tt>.qrc</tt> file can be compiled in the following way:</p> <pre> rcc -binary myresource.qrc -o myresource.rcc</pre> <p>In the application, this resource would be registered with code like this:</p> <pre> QResource::registerResource("/path/to/myresource.rcc");</pre> <a name="compiled-in-resources"></a> <h3>Compiled-In Resources</h3> <p>For a resource to be compiled into the binary the <tt>.qrc</tt> file must be mentioned in the application's <tt>.pro</tt> file so that <tt>qmake</tt> knows about it. For example:</p> <pre> RESOURCES = application.qrc</pre> <p><tt>qmake</tt> will produce make rules to generate a file called <tt>qrc_application.cpp</tt> that is linked into the application. This file contains all the data for the images and other resources as static C++ arrays of compressed binary data. The <tt>qrc_application.cpp</tt> file is automatically regenerated whenever the <tt>.qrc</tt> file changes or one of the files that it refers to changes. If you don't use <tt>.pro</tt> files, you can either invoke <tt>rcc</tt> manually or add build rules to your build system.</p> <p align="center"><img src="images/resources.png" alt="Building resources into an application" /></p><p>Currently, Qt always stores the data directly in the executable, even on Windows and Mac OS X, where the operating system provides native support for resources. This might change in a future Qt release.</p> <a name="using-resources-in-the-application"></a> <h2>Using Resources in the Application</h2> <p>In the application, resource paths can be used in most places instead of ordinary file system paths. In particular, you can pass a resource path instead of a file name to the <a href="qicon.html">QIcon</a>, <a href="qimage.html">QImage</a>, or <a href="qpixmap.html">QPixmap</a> constructor:</p> <pre> cutAct = new QAction(QIcon(":/images/cut.png"), tr("Cu&t"), this);</pre> <p>See the <a href="mainwindows-application.html">Application</a> example for an actual application that uses Qt's resource system to store its icons.</p> <p>In memory, resources are represented by a tree of resource objects. The tree is automatically built at startup and used by <a href="qfile.html">QFile</a> for resolving paths to resources. You can use a <a href="qdir.html">QDir</a> initialized with ":/" to navigate through the resource tree from the root.</p> <p>Qt's resources support the concept of a search path list. If you then refer to a resource with <tt>:</tt> instead of <tt>:/</tt> as the prefix, the resource will be looked up using the search path list. The search path list is empty at startup; call <a href="qdir-obsolete.html#addResourceSearchPath">QDir::addResourceSearchPath</a>() to add paths to it.</p> <p>If you have resources in a static library, you might need to force initialization of your resources by calling <a href="qdir.html#Q_INIT_RESOURCE">Q_INIT_RESOURCE</a>() with the base name of the <tt>.qrc</tt> file. For example:</p> <pre> int main(int argc, char *argv[]) { QApplication app(argc, argv); Q_INIT_RESOURCE(graphlib); ... return app.exec(); }</pre> <p>Similarly, if you must unload a set of resources explicitly (because a plugin is being unloaded or the resources are not valid any longer), you can force removal of your resources by calling <a href="qdir.html#Q_CLEANUP_RESOURCE">Q_CLEANUP_RESOURCE</a>() with the same base name as above.</p> <p /><address><hr /><div align="center"> <table width="100%" cellspacing="0" border="0"><tr class="address"> <td width="30%">Copyright © 2008 <a href="trolltech.html">Trolltech</a></td> <td width="40%" align="center"><a href="trademarks.html">Trademarks</a></td> <td width="30%" align="right"><div align="right">Qt 4.3.4</div></td> </tr></table></div></address></body> </html>