The Qt Resource System

Resource Collection Files (.qrc)

The resources associated with an application are specified in a .qrc 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.

Here's an example .qrc file:

    <!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>

The resource files listed in the .qrc file are files that are part of the application's source tree. Paths are relative to the directory where the .qrc file is located.

The .qrc file must be mentioned in the application's .pro file so that qmake knows about it. For example:

    RESOURCES     = application.qrc

qmake will produce make rules to generate a file called qrc_application.cpp 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 qrc_application.cpp file is automatically regenerated whenever the .qrc file changes or one of the files that it refers to changes. If you don't use .pro files, you can either invoke rcc manually or add build rules to your build system.

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.

By default, resources are accessible in the application under the same name as they have in the source tree, with a :/ prefix. For example, the path :/image/cut.png would give access to the cut.png file, whose location in the application's source tree is images/cut.png. This can be changed using the file tag's alias attribute:

    <file alias="cut-img.png">images/cut.png</file>

The file is then accessible as :/cut-img.png from the application. It is also possible to specify a path prefix for all files in the .qrc file using the qresource tag's prefix attribute:

    <qresource prefix="/myresources">
        <file alias="cut-img.png">images/cut.png</file>
    </qresource>

In this case, the file is accessible as :/myresources/cut-img.png.

Some resources, such as translation files and icons, many need to change based on the user's locale. This is possible using the lang attribute. For example:

    <qresource>
        <file>cut.jpg</file>
    </qresource>
    <qresource lang="fr">
        <file alias="cut.jpg">cut_fr.jpg</file>
    </qresource>

If the user's locale is French (i.e., QLocale::system().name() returns "fr_FR"), :/cut.jpg becomes a reference to the cut_fr.jpg image. For other locales, cut.jpg is used.

        cutAct = new QAction(QIcon(":/images/cut.png"), tr("Cu&t"), this);

    int main(int argc, char *argv[])
    {
        QApplication app(argc, argv);
        Q_INIT_RESOURCE(graphlib);
        ...
        return app.exec();
    }