cmake-qt(7)

Introduction

CMake can find and use Qt 4 and Qt 5 libraries. The Qt 4 libraries are found by the FindQt4 find-module shipped with CMake, whereas the Qt 5 libraries are found using “Config-file Packages” shipped with Qt 5. See cmake-packages(7) for more information about CMake packages, and see the Qt cmake manual for your Qt version.

Qt 4 and Qt 5 may be used together in the same CMake buildsystem:

cmake_minimum_required(VERSION 3.8.0 FATAL_ERROR)

project(Qt4And5)

set(CMAKE_AUTOMOC ON)

find_package(Qt5 COMPONENTS Widgets DBus REQUIRED)
add_executable(publisher publisher.cpp)
target_link_libraries(publisher Qt5::Widgets Qt5::DBus)

find_package(Qt4 REQUIRED)
add_executable(subscriber subscriber.cpp)
target_link_libraries(subscriber Qt4::QtGui Qt4::QtDBus)

A CMake target may not link to both Qt 4 and Qt 5. A diagnostic is issued if this is attempted or results from transitive target dependency evaluation.

Qt Build Tools

Qt relies on some bundled tools for code generation, such as moc for meta-object code generation, uic for widget layout and population, and rcc for virtual filesystem content generation. These tools may be automatically invoked by cmake(1) if the appropriate conditions are met. The automatic tool invocation may be used with both Qt 4 and Qt 5.

The tools are executed as part of a synthesized custom target generated by CMake. Target dependencies may be added to that custom target by adding them to the AUTOGEN_TARGET_DEPENDS target property.

AUTOMOC

The AUTOMOC target property controls whether cmake(1) inspects the C++ files in the target to determine if they require moc to be run, and to create rules to execute moc at the appropriate time.

If a macro from AUTOMOC_MACRO_NAMES is found in a header file, moc will be run on the file. The result will be put into a file named according to moc_<basename>.cpp. If the macro is found in a C++ implementation file, the moc output will be put into a file named according to <basename>.moc, following the Qt conventions. The <basename>.moc must be included by the user in the C++ implementation file with a preprocessor #include.

Included moc_*.cpp and *.moc files will be generated in the <AUTOGEN_BUILD_DIR>/include directory which is automatically added to the target’s INCLUDE_DIRECTORIES.

Not included moc_<basename>.cpp files will be generated in custom folders to avoid name collisions and included in a separate <AUTOGEN_BUILD_DIR>/mocs_compilation.cpp file which is compiled into the target.

The moc command line will consume the COMPILE_DEFINITIONS and INCLUDE_DIRECTORIES target properties from the target it is being invoked for, and for the appropriate build configuration.

The AUTOMOC target property may be pre-set for all following targets by setting the CMAKE_AUTOMOC variable. The AUTOMOC_MOC_OPTIONS target property may be populated to set options to pass to moc. The CMAKE_AUTOMOC_MOC_OPTIONS variable may be populated to pre-set the options for all following targets.

Additional macro names to search for can be added to AUTOMOC_MACRO_NAMES.

Additional moc dependency file names can be extracted from source code by using AUTOMOC_DEPEND_FILTERS.

Source C++ files can be excluded from AUTOMOC processing by enabling SKIP_AUTOMOC or the broader SKIP_AUTOGEN.

AUTOUIC

The AUTOUIC target property controls whether cmake(1) inspects the C++ files in the target to determine if they require uic to be run, and to create rules to execute uic at the appropriate time.

If a preprocessor #include directive is found which matches <path>ui_<basename>.h, and a <basename>.ui file exists, then uic will be executed to generate the appropriate file. The <basename>.ui file is searched for in the following places

  1. <source_dir>/<basename>.ui

  2. <source_dir>/<path><basename>.ui

  3. <AUTOUIC_SEARCH_PATHS>/<basename>.ui

  4. <AUTOUIC_SEARCH_PATHS>/<path><basename>.ui

where <source_dir> is the directory of the C++ file and AUTOUIC_SEARCH_PATHS is a list of additional search paths.

The generated generated ui_*.h files are placed in the <AUTOGEN_BUILD_DIR>/include directory which is automatically added to the target’s INCLUDE_DIRECTORIES.

The AUTOUIC target property may be pre-set for all following targets by setting the CMAKE_AUTOUIC variable. The AUTOUIC_OPTIONS target property may be populated to set options to pass to uic. The CMAKE_AUTOUIC_OPTIONS variable may be populated to pre-set the options for all following targets. The AUTOUIC_OPTIONS source file property may be set on the <basename>.ui file to set particular options for the file. This overrides options from the AUTOUIC_OPTIONS target property.

A target may populate the INTERFACE_AUTOUIC_OPTIONS target property with options that should be used when invoking uic. This must be consistent with the AUTOUIC_OPTIONS target property content of the depender target. The CMAKE_DEBUG_TARGET_PROPERTIES variable may be used to track the origin target of such INTERFACE_AUTOUIC_OPTIONS. This means that a library which provides an alternative translation system for Qt may specify options which should be used when running uic:

add_library(KI18n klocalizedstring.cpp)
target_link_libraries(KI18n Qt5::Core)

# KI18n uses the tr2i18n() function instead of tr().  That function is
# declared in the klocalizedstring.h header.
set(autouic_options
  -tr tr2i18n
  -include klocalizedstring.h
)

set_property(TARGET KI18n APPEND PROPERTY
  INTERFACE_AUTOUIC_OPTIONS ${autouic_options}
)

A consuming project linking to the target exported from upstream automatically uses appropriate options when uic is run by AUTOUIC, as a result of linking with the IMPORTED target:

set(CMAKE_AUTOUIC ON)
# Uses a libwidget.ui file:
add_library(LibWidget libwidget.cpp)
target_link_libraries(LibWidget
  KF5::KI18n
  Qt5::Widgets
)

Source files can be excluded from AUTOUIC processing by enabling SKIP_AUTOUIC or the broader SKIP_AUTOGEN.

AUTORCC

The AUTORCC target property controls whether cmake(1) creates rules to execute rcc at the appropriate time on source files which have the suffix .qrc.

add_executable(myexe main.cpp resource_file.qrc)

The AUTORCC target property may be pre-set for all following targets by setting the CMAKE_AUTORCC variable. The AUTORCC_OPTIONS target property may be populated to set options to pass to rcc. The CMAKE_AUTORCC_OPTIONS variable may be populated to pre-set the options for all following targets. The AUTORCC_OPTIONS source file property may be set on the <name>.qrc file to set particular options for the file. This overrides options from the AUTORCC_OPTIONS target property.

Source files can be excluded from AUTORCC processing by enabling SKIP_AUTORCC or the broader SKIP_AUTOGEN.

Visual Studio Generators

When using the Visual Studio generators CMake tries to use a PRE_BUILD custom command instead of a custom target for autogen. PRE_BUILD can’t be used when the autogen target depends on files. This happens when

qtmain.lib on Windows

The Qt 4 and 5 IMPORTED targets for the QtGui libraries specify that the qtmain.lib static library shipped with Qt will be linked by all dependent executables which have the WIN32_EXECUTABLE enabled.

To disable this behavior, enable the Qt5_NO_LINK_QTMAIN target property for Qt 5 based targets or QT4_NO_LINK_QTMAIN target property for Qt 4 based targets.

add_executable(myexe WIN32 main.cpp)
target_link_libraries(myexe Qt4::QtGui)

add_executable(myexe_no_qtmain WIN32 main_no_qtmain.cpp)
set_property(TARGET main_no_qtmain PROPERTY QT4_NO_LINK_QTMAIN ON)
target_link_libraries(main_no_qtmain Qt4::QtGui)