Errors in generated MOC files for QT5 from cmake

Question

I generated moc files for QT5 using

set (CMAKE_AUTOMOC ON)
set(CMAKE_INCLUDE_CURRENT_DIR ON)

Then I add the moc files into SRC using

SET(SRC
  src/main.cpp
  src/video_widget_surface.cpp
  src/video_widget.cpp
  src/video_player.cpp
#moc files
  moc/moc_video_player.cpp
  moc/moc_video_widget.cpp
  moc/moc_video_widget_surface.cpp

Finally I add the executable using

add_executable(somegui ${SRC})

But I get errors in moc files saying :

/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:54:6: error: 'VideoWidget' has not been declared
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:62:19: error: 'VideoWidget' has not been declared
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:68:20: error: 'VideoWidget' has not been declared
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:68:46: error: non-member function 'const QMetaObject* metaObject()' cannot have cv-qualifier
/other/Qt5.0.1/5.0.1/gcc_64/include/QtCore/qobject.h: In function 'const QMetaObject* metaObject()':
/other/Qt5.0.1/5.0.1/gcc_64/include/QtCore/qobject.h:401:33: error: 'QScopedPointer<QObjectData> QObject::d_ptr' is protected
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:70:21: error: within this context
/other/Qt5.0.1/5.0.1/gcc_64/include/QtCore/qobject.h:401:33: error: invalid use of non-static data member 'QObject::d_ptr'
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:70:21: error: from this location
/other/Qt5.0.1/5.0.1/gcc_64/include/QtCore/qobject.h:401:33: error: 'QScopedPointer<QObjectData> QObject::d_ptr' is protected
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:70:50: error: within this context
/other/Qt5.0.1/5.0.1/gcc_64/include/QtCore/qobject.h:401:33: error: invalid use of non-static data member 'QObject::d_ptr'
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:70:50: error: from this location
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp: At global scope:
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:73:7: error: 'VideoWidget' has not been declared
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp: In function 'void* qt_metacast(const char*)':
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:77:47: error: expected type-specifier before 'VideoWidget'
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:77:47: error: expected '>' before 'VideoWidget'
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:77:47: error: expected '(' before 'VideoWidget'
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:77:47: error: 'VideoWidget' was not declared in this scope
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:77:59: error: expected primary-expression before '>' token
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:77:61: error: invalid use of 'this' in non-member function
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:77:67: error: expected ')' before ';' token
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:78:40: error: cannot call member function 'virtual void* QWidget::qt_metacast(const char*)' without object
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp: At global scope:
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:81:5: error: 'VideoWidget' has not been declared
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp: In function 'int qt_metacall(QMetaObject::Call, int, void**)':
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:83:43: error: cannot call member function 'virtual int QWidget::qt_metacall(QMetaObject::Call, int, void**)' without object
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp: In function 'void* qt_metacast(const char*)':
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:79:1: warning: control reaches end of non-void function [-Wreturn-type]
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp: In function 'const QMetaObject* metaObject()':
/other/workspace/perception/somestuff/moc/moc_video_widget.cpp:71:1: warning: control reaches end of non-void function [-Wreturn-type]
make[2]: *** [CMakeFiles/somestuff.dir/moc/moc_video_widget.cpp.o] Error 1
make[1]: *** [CMakeFiles/somestuff.dir/all] Error 2
make: *** [all] Error 2

My understanding is that there is some error in the moc files that are created. But I don't have any control over how that is created. Now how do I solve this bug ?

Answer 1

CMake documentation is not that bad, do not neglect reading it. You misunderstood the concept of AUTOMOC:

AUTOMOC is a boolean specifying whether CMake will handle the Qt moc preprocessor automatically, i.e. without having to use the QT4_WRAP_CPP() macro. Currently Qt4 is supported. When this property is set to TRUE, CMake will scan the source files at build time and invoke moc accordingly. If an #include statement like #include "moc_foo.cpp" is found, the Q_OBJECT class declaration is expected in the header, and moc is run on the header file. If an #include statement like #include "foo.moc" is found, then a Q_OBJECT is expected in the current source file and moc is run on the file itself. Additionally, all header files are parsed for Q_OBJECT macros, and if found, moc is also executed on those files.

So, first of all, you should not add generated moc files explicitly to sources and push them into executable compilation. In other words, you only push your sources:

SET(SRC
  src/main.cpp
  src/video_widget_surface.cpp
  src/video_widget.cpp
  src/video_player.cpp)

and moc ones are handled automatically by CMake.

Secondly, as stated in the documentation:

• If Q_OBJECT is in the foo.h (i.e. QObject is declared in the header file), then in the corresponding foo.cpp don't forget to add #include "moc_foo.cpp", preferably at the end of the file;

• If Q_OBJECT is in the foo.cpp (i.e. QObject is declared in the source file), then, again, in the foo.cpp itself don't forget to add #include "foo.moc", preferably at the end of the file.