You can use the qt.conf file to override paths or to specify arguments to be passed to the platform plugins.

Format and Location

The qt.conf file is an INI text file, as described in the QSettings documentation.

QLibraryInfo will load qt.conf from one of the following locations:

1. :/qt/etc/qt.conf using the resource system
2. on macOS, in the Resource directory inside the application bundle, for example assistant.app/Contents/Resources/qt.conf
3. in the directory containing the application executable, i.e. QCoreApplication::applicationDirPath() + QDir::separator() + "qt.conf"

Overriding Paths

The qt.conf file can be used to override the hard-coded paths that are compiled into the Qt library. These paths are accessible using the QLibraryInfo class. Without qt.conf, the functions in QLibraryInfo return these hard-coded paths; otherwise they return the paths as specified in qt.conf.

Without qt.conf, the Qt libraries will use the hard-coded paths to look for plugins, translations, and so on. These paths may not exist on the target system, or they may not be accessible. Because of this, you may need qt.conf to make the Qt libraries look elsewhere.

The file should have a Paths group which contains the entries that correspond to each value of the QLibraryInfo::LibraryLocation enum. See the QLibraryInfo documentation for details on the meaning of the various locations.

Absolute paths are used as specified in the qt.conf file. All paths are relative to the Prefix. On Windows and X11, the Prefix is relative to the directory containing the application executable (QCoreApplication::applicationDirPath()). On macOS, the Prefix is relative to the Contents in the application bundle. For example, application.app/Contents/plugins/ is the default location for loading Qt plugins. Note that the plugins need to be placed in specific sub-directories under the plugins directory (see How to Create Qt Plugins for details).

For example, a qt.conf file could contain the following:

[Paths]
Prefix = /some/path
Translations = i18n

Note: The backslash character is treated as a special character in INI files (see QSettings). It is therefore recommended to use forward slashes for paths on Windows as well. Otherwise, an escape character is required:

Prefix = c:\\SomePath

Configuring Arguments to the Platform Plugins

The qt.conf may contain a Platforms group, whose keys are comma-delimited lists of arguments to be passed to the platform plugin. The key name is the name of the platform plugin with the first letter upper-cased followed by Arguments.

For example:

[Platforms]
WindowsArguments = fontengine=freetype

would cause the Windows platform plugin to use the FreeType font engine.

How to deal with parallel installations of older Qt versions

For environments that require an installation of an earlier major version of Qt as well, it is possible to use a version-specific qt.conf. This is often necessary in transition phases from one Qt version to the next, or to avoid conflicts caused by an existing file without version.

For this purpose, a file named qt6.conf can be used instead of the qt.conf file. If both files exist in the directory described above, qt6.conf is used.