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Force Moc to moc a file



  • Hi All,

    I've got an issue, that moc doesn't moc a file it should moc, under the following circumstances ( This is not exactly my situation, but explains resp. reproduces the problem):

    Suppose you have a macro defined in a header file - say foo.h:

    // in foo.h
    #define MAKE_TYPE(name) class name: public QObject { Q_OBJECT public: name() : QObject(0) {} };
    

    and a definition in the same file, like

    // in foo.h
    MAKE_TYPE(MyType)
    

    Then I can create an instance of MyType in any other file without any problems.

    // any file
    MyType t
    

    Do I move the definition in another file - say bar.h

    // in bar.h
    MAKE_TYPE(MyType)
    

    I get a couple of undefined references, when I create the Instance. This is because bar.h is not mocced ( is this the right word ?).
    To get it work, I have to put a dummy QObject in bar.h, like:

    // in bar.h
    class DummyQObj : public QObject { Q_OBJECT public: DummyQObj() : QObject(0) {} };
    MAKE_TYPE(MyType)
    

    The it's mocced and it works.
    So my question is, is there any way to tell the moc ( p.e. by means of a define ) to moc the file, although it thinks it shouldn't ?

    Or is this even a bug ?

    Thanks,
    Martin



  • HI and welcome to devnet

    @matze42 said:

    I get a couple of undefined references, when I create the Instance. This is because bar.h is not

    can you post the errors? Probably could be better to include <QObject> in the macro.

    BTW, Q_OBJECT is itself a macro; I suggest to define your macro in multi-line mode

    #define MAKE_TYPE(name) \
    #include <QObject>
    class name: public QObject \
    { \
    Q_OBJECT \
    public: \
      name(): QObject(0) {} \
    };
    


  • Hi ,

    thanks for your answer.

    the error is

    error: undefined reference to `vtable for MyType'
    

    This is clear, as the moc file is not generated.

    ... and the original macro is of course defined in multiline mode, the posted example is only a condensed version.

    Additionally including <QObject> doesn't help ( btw: the way you posted it leads to preprocessor errors ).



  • @matze42 said:

    Additionally including <QObject> doesn't help ( btw: the way you posted it leads to preprocessor errors ).

    Yep, I forgot \ at the end of the line.
    Can you post you .pro file? Are your headers in the HEADERS variable

    what happens if you run manually moc on this header file?



  • Hi,

    I simplified it and it looks like this:

    QT       += core
    QT       -= gui
    
    TARGET = moctest
    CONFIG   += console
    CONFIG   -= app_bundle
    
    TEMPLATE = app
    
    SOURCES += main.cpp \
        bar.cpp \
        foo.cpp
    
    HEADERS += \
        foo.h \
        bar.h
    
    // main.cpp
    #include "foo.h"
    #include "bar.h"
    
    #include <QCoreApplication>
    
    int main(int argc, char *argv[])
    {
        QCoreApplication a(argc, argv);
    
        MyType t;
        MyOtherType ot;
    
        return a.exec();
    }
    
    // foo.h
    #ifndef FOO_H
    #define FOO_H
    
    #include <QObject>
    
    #define MAKE_TYPE(name) \
        class name: public QObject \
       { \
        Q_OBJECT \
        public: name() : QObject(0) {}\
        };
    
    MAKE_TYPE(MyType)
    
    #endif // FOO_H
    
    // bar.h
    #ifndef BAR_H
    #define BAR_H
    
    #include "foo.h"
    #include <QObject>
    
    // With this uncommented it works
    //class DummyQObj : public QObject { Q_OBJECT public: DummyQObj() : QObject(0) {} };
    
    MAKE_TYPE(MyOtherType)
    
    #endif // BAR_H
    
    // foo.cpp
    #include "foo.h"
    
    // bar.cpp
    #include "bar.h"
    

    Just try it.
    ( Don't forget do completey cleanup your build directory after changing something, sometimes the object files are kept )

    Btw: Is it possible in this forum to attach files to posts ? Then I could attach my project directly.



  • This post is deleted!


  • HI,

    my guess is that qmake force moc to be called only for header files where Q_OBJECT is used. qmake runs before the preprocessor so in your project it doesn't see the Q_OBJECT macro inside bar.h



  • Hi,

    ... yes, that was my original question.
    Quote from Post:
    So my question is, is there any way to tell the moc ( p.e. by means of a define ) to moc the file, although it thinks it shouldn't ?

    Of course I can put some Q_OBJECT somewhere on the top of the file, p.e.:

    #ifdef SOMETHING_WHICH_DEFINITELY_IS_NOT_DEFINED_ELSEWHERE
        Q_OBJECT
    #endif
    

    where it's just there, but not evaluated.
    But this looks pretty hacky and not nice.

    I rather would like something like;

    #define Q_FORCE_MOC
    

  • Lifetime Qt Champion

    Hi,

    Out of curiosity, which version of Qt are we talking about ?



  • Hi,

    thanks for asking - i missed that:
    Qt 5.4 on Xubuntu 14.



  • Ok,

    I understand, that qmakedoes not recognize ( and probably even cannot - as it supposed doesn't expand macros) that the concerning file needs to get mocced.
    Is there any ways then to add something in the pro file to tell qmake, that the file needs to get mocced ? p.e.:

    moc += bar.h
    

  • Lifetime Qt Champion

    qmake is a project manager so indeed it doesn't include macro expansion. moc on the other end (since Qt 5) should expand macro properly.

    I just tested your code on OS X and it worked



  • Hi SGaist,

    thanx for caring about this issue,
    Did yout test it without the Q_OBJECT pseudo code commented or uncommented ?

    In the meanwhile I started to redesign this part of our software (we are talking about 70-80 type definitions in about 7-8 namespaces resp. files ) - but anyway it would be quite interesting ( at least for me ) to know, if such kind of constructs make sense in the Qt world or not.


  • Lifetime Qt Champion

    I've removed/re-added it and it still builds. Q_OBJECT is useful when you implement e.g. signals and slots



  • Strange !

    Seems, that my qmake implementation is different from yours.

    Reproducable it builds if I have the Q_OBJECT uncommented, and it gives me the linker errors if i have it commented.

    So this led me to the assumption, that a (uncommented) Q_OBJECT occurance in a header file is the hint for qmake to mark it to be mocced.


  • Lifetime Qt Champion

    Which version of qmake are you using ?



  • Qt 5.4.0 GCC 64bit on Xubuntu 14 64bit.


  • Lifetime Qt Champion

    Are you calling qmake through Qt Creator or on the command line ?



  • By QtCreator


  • Lifetime Qt Champion

    Did you re-try with Qt 5.5 ?


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