# AUTOMOC

Should the target be processed with auto-moc (for Qt projects).

`AUTOMOC` is a boolean specifying whether CMake will handle the Qt `moc` preprocessor automatically, i.e. without having to use commands like `QT4_WRAP_CPP()`, qt5_wrap_cpp(), etc. Currently, Qt versions 4 to 6 are supported.

This property is initialized by the value of the `CMAKE_AUTOMOC` variable if it is set when a target is created.

When this property is set `ON`, CMake will scan the header and source files at build time and invoke `moc` accordingly.

## Header file processing

At configuration time, a list of header files that should be scanned by `AUTOMOC` is computed from the target's sources.

- All header files in the target's sources are added to the scan list.

- For all C++ source files `<source_base>.<source_extension>` in the target's sources, CMake searches for

  - a regular header with the same base name (`<source_base>.<header_extension>`) and

  - a private header with the same base name and a `_p` suffix (`<source_base>_p.<header_extension>`)

  and adds these to the scan list.

At build time, CMake scans each unknown or modified header file from the list and searches for

- a Qt macro from `AUTOMOC_MACRO_NAMES`,

- additional file dependencies from the `FILE` argument of a `Q_PLUGIN_METADATA` macro and

- additional file dependencies detected by filters defined in `AUTOMOC_DEPEND_FILTERS`.

If a Qt macro is found, then the header will be compiled by the `moc` to the output file `moc_<base_name>.cpp`. The complete output file path is described in the section Output file location.

The header will be `moc` compiled again if a file from the additional file dependencies changes.

Header `moc` output files `moc_<base_name>.cpp` can be included in source files. In the section Including header moc files in sources there is more information on that topic.

## Source file processing

At build time, CMake scans each unknown or modified C++ source file from the target's sources for

- a Qt macro from `AUTOMOC_MACRO_NAMES`,

- includes of header `moc` files (see Including header moc files in sources),

- additional file dependencies from the `FILE` argument of a `Q_PLUGIN_METADATA` macro and

- additional file dependencies detected by filters defined in `AUTOMOC_DEPEND_FILTERS`.

If a Qt macro is found, then the C++ source file `<base>.<source_extension>` is expected to as well contain an include statement

    #include <<base>.moc> // or
    #include "<base>.moc"

The source file then will be compiled by the `moc` to the output file `<base>.moc`. A description of the complete output file path is in section Output file location.

The source will be `moc` compiled again if a file from the additional file dependencies changes.

### Including header moc files in sources

A source file can include the `moc` output file of a header `<header_base>.<header_extension>` by using an include statement of the form

    #include <moc_<header_base>.cpp> // or
    #include "moc_<header_base>.cpp"

If the `moc` output file of a header is included by a source, it will be generated in a different location than if it was not included. This is described in the section Output file location.

## Output file location

### Included moc output files

`moc` output files that are included by a source file will be generated in

- `<AUTOGEN_BUILD_DIR>/include` for single configuration generators or in

- `<AUTOGEN_BUILD_DIR>/include_<CONFIG>` for `multi configuration` generators.

Where `<AUTOGEN_BUILD_DIR>` is the value of the target property `AUTOGEN_BUILD_DIR`.

The include directory is automatically added to the target's `INCLUDE_DIRECTORIES`.

### Not included moc output files

`moc` output files that are not included in a source file will be generated in

- `<AUTOGEN_BUILD_DIR>/<SOURCE_DIR_CHECKSUM>` for single configuration generators or in,

- `<AUTOGEN_BUILD_DIR>/include_<CONFIG>/<SOURCE_DIR_CHECKSUM>` for `multi configuration` generators.

Where `<SOURCE_DIR_CHECKSUM>` is a checksum computed from the relative parent directory path of the `moc` input file. This scheme allows to have `moc` input files with the same name in different directories.

All not included `moc` output files will be included automatically by the CMake generated file

- `<AUTOGEN_BUILD_DIR>/mocs_compilation.cpp`, or

- `<AUTOGEN_BUILD_DIR>/mocs_compilation_$<CONFIG>.cpp`,

which is added to the target's sources.

## Qt version detection

`AUTOMOC` enabled targets need to know the Qt major and minor version they're working with. The major version usually is provided by the `INTERFACE_QT_MAJOR_VERSION` property of the `Qt[456]Core` library, that the target links to. To find the minor version, CMake builds a list of available Qt versions from

- `Qt6Core_VERSION_MAJOR` and `Qt6Core_VERSION_MINOR` variables (usually set by `find_package(Qt6...)`)

- `Qt6Core_VERSION_MAJOR` and `Qt6Core_VERSION_MINOR` directory properties

- `Qt5Core_VERSION_MAJOR` and `Qt5Core_VERSION_MINOR` variables (usually set by `find_package(Qt5...)`)

- `Qt5Core_VERSION_MAJOR` and `Qt5Core_VERSION_MINOR` directory properties

- `QT_VERSION_MAJOR` and `QT_VERSION_MINOR` variables (usually set by `find_package(Qt4...)`)

- `QT_VERSION_MAJOR` and `QT_VERSION_MINOR` directory properties

in the context of the `add_executable()` or `add_library()` call.

Assumed `INTERFACE_QT_MAJOR_VERSION` is a valid number, the first entry in the list with a matching major version is taken. If no matching major version was found, an error is generated. If `INTERFACE_QT_MAJOR_VERSION` is not a valid number, the first entry in the list is taken.

A `find_package(Qt[456]...)` call sets the `QT/Qt[56]Core_VERSION_MAJOR/MINOR` variables. If the call is in a different context than the `add_executable()` or `add_library()` call, e.g. in a function, then the version variables might not be available to the `AUTOMOC` enabled target. In that case the version variables can be forwarded from the `find_package(Qt[456]...)` calling context to the `add_executable()` or `add_library()` calling context as directory properties. The following Qt5 example demonstrates the procedure.

    function (add_qt5_client)
      find_package(Qt5 REQUIRED QUIET COMPONENTS Core Widgets)
      ...
      set_property(DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}"
        PROPERTY Qt5Core_VERSION_MAJOR "${Qt5Core_VERSION_MAJOR}")
      set_property(DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}"
        PROPERTY Qt5Core_VERSION_MINOR "${Qt5Core_VERSION_MAJOR}")
      ...
    endfunction ()
    ...
    add_qt5_client()
    add_executable(myTarget main.cpp)
    target_link_libraries(myTarget Qt5::QtWidgets)
    set_property(TARGET myTarget PROPERTY AUTOMOC ON)

## Modifiers

`AUTOMOC_EXECUTABLE`: The `moc` executable will be detected automatically, but can be forced to a certain binary using this target property.

`AUTOMOC_MOC_OPTIONS`: Additional command line options for `moc` can be set in this target property.

`AUTOMOC_MACRO_NAMES`: This list of Qt macro names can be extended to search for additional macros in headers and sources.

`AUTOMOC_DEPEND_FILTERS`: `moc` dependency file names can be extracted from headers or sources by defining file name filters in this target property.

`AUTOMOC_COMPILER_PREDEFINES`: Compiler pre definitions for `moc` are written to the `moc_predefs.h` file. The generation of this file can be enabled or disabled in this target property.

`SKIP_AUTOMOC`: Sources and headers can be excluded from `AUTOMOC` processing by setting this source file property.

`SKIP_AUTOGEN`: Source files can be excluded from `AUTOMOC`, `AUTOUIC` and `AUTORCC` processing by setting this source file property.

`AUTOGEN_SOURCE_GROUP`: This global property can be used to group files generated by `AUTOMOC` or `AUTORCC` together in an IDE, e.g. in MSVS.

`AUTOGEN_TARGETS_FOLDER`: This global property can be used to group `AUTOMOC`, `AUTOUIC` and `AUTORCC` targets together in an IDE, e.g. in MSVS.

`CMAKE_GLOBAL_AUTOGEN_TARGET`: A global `autogen` target, that depends on all `AUTOMOC` or `AUTOUIC` generated The <ORIGIN>_autogen target targets in the project, will be generated when this variable is `ON`.

`AUTOGEN_PARALLEL`: This target property controls the number of `moc` or `uic` processes to start in parallel during builds.

`AUTOGEN_COMMAND_LINE_LENGTH_MAX`: This target property controls the limit when to use response files for `moc` or `uic` processes on Windows.

See the `cmake-qt(7)` manual for more information on using CMake with Qt.