fail to use Q_OBJECT Macro in CMake Project



  • I am having trouble with the meta Object Compiler of Qt in my CMake Project. A shared lib I am building contains the following code and employs the pimpl idiom. After invoking CMake and upon compilation I get

    AUTOGEN: error: ~/tools/Project/gui/src/mainWindow.cpp: The file contains a Q_OBJECT macro, but does not include "mainWindow.moc" ! gui/CMakeFiles/gui_automoc.dir/build.make:57: recipe for target 'gui/CMakeFiles/gui_automoc' failed make[2]: *** [gui/CMakeFiles/gui_automoc] Error 1 CMakeFiles/Makefile2:234: recipe for target 'gui/CMakeFiles/gui_automoc.dir/all' failed
    

    I dont get what I am doing wrong or whats the correct way to incorporate src files with the Q_OBJECT Macro in my project.

    Please help =/

    gui/src/mainWindow.hpp

    
    #include <QMainWindow>
    #include <string>
    
    
    class MainWindow : public QMainWindow {
      class MainWindowImpl;
    
     public:
      MainWindow(QWidget* parent = nullptr);
    
     private:
      MainWindowImpl* pimpl_;
    };
    gui/include/gui/mainWindow.cpp
    
    #include "gui/mainWindow.hpp"
    
    class MainWindow::MainWindowImpl : public QWidget{
     Q_OBJECT
      public:
       explicit MainWindowImpl(MainWindow *parent);
    
      private:
       MainWindow &parent_;
    };
    
    MainWindow::MainWindowImpl::MainWindowImpl(MainWindow *parent)
        : QWidget{parent}, parent_(*parent) {}
    
    MainWindow::MainWindow(QWidget *parent) : QMainWindow{parent} {
        pimpl_ = new MainWindowImpl{this};
        setCentralWidget(pimpl_);
    }
    

    I compile the library like so:

    cmake_minimum_required(VERSION 3.5.1 FATAL_ERROR)
    project(gui)
    
    add_library(${PROJECT_NAME}
      SHARED
       src/mainWindow.cpp
    )
    add_library(gui::gui ALIAS ${PROJECT_NAME})
    
    target_include_directories(${PROJECT_NAME} 
      PUBLIC 
       ${PROJECT_SOURCE_DIR}/include
    )
    
    set_target_properties(${PROJECT_NAME} PROPERTIES AUTOMOC TRUE)
    
    target_link_libraries(${PROJECT_NAME}
      PUBLIC
       Qt5::Widgets
       Qt5::Core
       Qt5::Xml
       Qt5::OpenGL
       Qt5::Gui
    )
    
    install(TARGETS ${PROJECT_NAME} DESTINATION lib)
    

    Now I want to link this lib against my executable

    apps/main.cpp
    
    #include <QApplication>
    #include "gui/mainWindow.hpp"
    
    int main(int argc, char *argv[]) {
    
    QApplication app{argc, argv};
    
    MainWindow gui{};
    gui.show();
    
    return app.exec();
    }
    

    with the following CMakelists.txt where I link against the gui lib

    cmake_minimum_required (VERSION 3.5.1 FATAL_ERROR)
    project (app)
    
    add_executable(${PROJECT_NAME}
      main.cpp
    )
    
    target_include_directories(${PROJECT_NAME}
        PUBLIC ${PROJECT_BINARY_DIR}
    )
    
    target_link_libraries(${PROJECT_NAME}
      PRIVATE
       gui::gui
       Qt5::Widgets
       Qt5::Core
       Qt5::Xml
       Qt5::OpenGL
       Qt5::Gui
     )
    
     install(TARGETS ${PROJECT_NAME}
             DESTINATION bin)
    

    my top-level CMakeLists of the project looks like the following

    cmake_minimum_required (VERSION 3.5.1 FATAL_ERROR)
    project(project)
    
    set(CMAKE_INSTALL_DIR ${PROJECT_SOURCE_DIR}/obj)
    set(CMAKE_INSTALL_PREFIX  ${CMAKE_INSTALL_DIR})
    # add our local path to the runtime path
    SET(CMAKE_INSTALL_RPATH "$ORIGIN:${CMAKE_INSTALL_PREFIX}/lib")
    # also add the link paths to the runtime paths
    SET(CMAKE_INSTALL_RPATH_USE_LINK_PATH TRUE)
    
    find_package(Qt5 COMPONENTS Core Widgets Xml OpenGL Gui REQUIRED)
    
    ## --> Build libraries and applications  <--
    add_subdirectory(gui)
    add_subdirectory(apps)
    


  • Anyone? I am losing my mind over here -.-



  • @Sewing said in fail to use Q_OBJECT Macro in CMake Project:

    Anyone?

    It's only 2 hours since your initial post. Please show a little more patience, like 24 hours. It's always nighttime for half of the community. And it's friday.


  • Lifetime Qt Champion

    Hi,

    Did you already took a look at the CMake Manual from Qt's documentation ?



  • I did, but without being able to infer any conclusive hints from the article towards a solution for my problem



  • The problem is not CMake:

    @Sewing said in fail to use Q_OBJECT Macro in CMake Project:

    mainWindow.cpp: The file contains a Q_OBJECT macro

    from http://doc.qt.io/qt-5/moc.html

    The moc tool reads a C++ header file.

    Did you declare a class with Q_OBJECT in a .cpp file? if so either yo do as the compiler tells you and #include "mainWindow.moc" (this file name might change depending on how moc gets invoked) at the end of the file or, as I would recommend, move it into a header



  • Mh difficult since I employ the pimpl idiom in which the nested implementation class in defined entirely within the source file


  • Lifetime Qt Champion

    Then move the private declaration part in its own header that you only include in the implementation part.

    Note that your MainWindow implementation looks a bit convoluted, you might be over-engineering some things.



  • thank you for the help.

    you mean cuz of using pimpl? this is just a minimal example and my intention was, to keep the public interface of mainwindow.cpp quite clean and readable



  • @Sewing said in fail to use Q_OBJECT Macro in CMake Project:

    pimpl idiom in which the nested implementation class in defined entirely within the source file

    You can move it into a header file, Qt does it all the time, they use _p.h suffix to mark private headers. For example: QDateTimePrivate



  • so if I understood correctly, the reason of having to do this is that the Q_OBJECT Macro has to be defined in the header file instead of the source file?

    and after doing so, is the line

    set_target_properties(${PROJECT_NAME} PROPERTIES AUTOMOC TRUE)
    

    sufficient for invoking the MOC in my CMakeLists file?



  • @SGaist said in fail to use Q_OBJECT Macro in CMake Project:

    Did you already took a look at the CMake Manual from Qt's documentation ?

    @Sewing said in fail to use Q_OBJECT Macro in CMake Project:

    I did

    from http://doc.qt.io/qt-5/cmake-manual.html:

    # Instruct CMake to run moc automatically when needed.
    set(CMAKE_AUTOMOC ON)
    


  • I read that, just thought variables in CMake are old-style while target_properties are the modern way to handle things



  • I heard opposing arguments to that when it comes to moc/rcc/uic. Personally, I use the set(CMAKE_AUTOMOC ON) way


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