Shared library on windows fails when using moc

[Christian Ehrlicher]

I don't see the include of the generated moc file 'moc_qpow.h' in your code.

[Mesrine]

@Christian-Ehrlicher
Where should i put this on qpow.cpp?

[Christian Ehrlicher]

@Mesrine doesn't matter - includes should go to the top.

[Mesrine]

@Mesrine

I have checked the moc produced source in windows
The file is inside build/qpow_autogen/652RYH7CFW/moc_qpow.cpp and the symbol the linker is complaining is defined like this:

Q_CONSTINIT const QMetaObject qiota::qpow::nonceFinder::staticMetaObject = { {
    QMetaObject::SuperData::link<QObject::staticMetaObject>(),
    qt_meta_stringdata_CLASSqiotaSCOPEqpowSCOPEnonceFinderENDCLASS.offsetsAndSizes,
    qt_meta_data_CLASSqiotaSCOPEqpowSCOPEnonceFinderENDCLASS,
    qt_static_metacall,
    nullptr,
    qt_incomplete_metaTypeArray<qt_meta_stringdata_CLASSqiotaSCOPEqpowSCOPEnonceFinderENDCLASS_t,
        // Q_OBJECT / Q_GADGET
        QtPrivate::TypeAndForceComplete<nonceFinder, std::true_type>,
        // method 'nonce_found'
        QtPrivate::TypeAndForceComplete<void, std::false_type>,
        QtPrivate::TypeAndForceComplete<quint64, std::false_type>,
        // method 'nonce_not_found'
        QtPrivate::TypeAndForceComplete<void, std::false_type>
    >,
    nullptr
} };

Due to the fact that the linker only complains when building shared library on windows and i have also tried

#include "qpow.moc"

on the class source giving me the same error.
Could it be that moc is not exporting the symbol for windows(like using Q_DECL_EXPORT and Q_DECL_IMPORT in the definition) ?

[Mesrine]

@Mesrine
So the QObject macro will expand in my class and declare the missing symbol on my class header file like

public: static struct QMetaObject const qiota::qpow::WorkerThread::staticMetaObject.

This symbol is then defined in the moc generated sources that can be included on the class source file or the resulting .obj can be linked to the library.

But the thing is that the expansion of QObject in my class maybe do not put

public: 
Q_DECL_EXPORT(Q_DECL_IMPORT) static struct QMetaObject const qiota::qpow::WorkerThread::staticMetaObject.

So the symbol is not correctly (exported)imported for windows shared.
Is this reasoning correct?

[Mesrine]

@Mesrine
You can see a much simpler reproducible example of the issue here

[Christian Ehrlicher]

And even there I don't see where you include "moc_foo.cpp" for AUTOMOC or do the moc by yourself anywhere.

[Mesrine]

@Christian-Ehrlicher
According to qt I do not need to include the header moc files when using cmake.
I will try and let you know.

[Mesrine]

@Mesrine
As maybe you can see the build fail with the same error.
But you can check now that the files are included.

[Mesrine]

@Christian-Ehrlicher
The Automoc is done automatically
as i have added in CMakeLists.txt

qt_standard_project_setup()

that this set AUTOMOC variable ON.

[Christian Ehrlicher]

I did not see (and not use by myself) qt_standard_project_setup() so you're correct with the automoc.

You use the same define for the export definition for both libraries - how should this work?

[JoeCFD]

@Mesrine

your libA uses libB. libA imports libB. So do not define WINDOWS_SHAREDLIB in libA
target_compile_definitions(libA PRIVATE WINDOWS_SHAREDLIB) <= can not have this one?

#if defined(WINDOWS_SHAREDLIB)
# define SHAREDLIB_EXPORT Q_DECL_EXPORT
#else
#define SHAREDLIB_EXPORT Q_DECL_IMPORT  <===libA needs this one if WINDOWS_SHAREDLIB is not defined.
#endif

[Mesrine]

@Christian-Ehrlicher
Thats a good point. Thanks!
Using the same definition for both libraries if not included correctly the headers could define the export on the symbol that should have an import statement.

This is not completely clear to me so Let me try.
I let you know :).

Yes, that was the problem. Many thanks.