CODEWITHSUNDEEP
c++qtqcoreapplication
feedc0de
feedc0de

Reputation: 3796

Q_COREAPP_STARTUP_FUNCTION with static class member method

I need to register my class using qRegisterMetaType() and wanted to use Q_COREAPP_STARTUP_FUNCTION.

I dont want to register it in main() because I need this in a (not statically linked) library.

void someUniqueMethodName()
{
    qRegisterMetaType(MyClass*);
}

Q_COREAPP_STARTUP_FUNCTION(someUniqueMethodName)

I have multiple cases for this and I dont want to pollute the root namespace. The compiler does not want multiple methods with the same name and I dont want to think about unique method names every time I am adding a new one.

Hence the static member method in my classes!

But this example does not compile:

class MyClass {
public:
    // ...
    static void registerMetaType();
}

with the implemention in .cpp file:

MyClass::registerMetaType() {}

Q_COREAPP_STARTUP_FUNCTION(MyClass::registerMetaType)

Why can't I use static member methods and if this isn't the correct way to solve this, what would be a better one?

UPDATE Compiler error messages:

/path/to/myclass.cpp:183:1: error: no ‘void MyClass::registerMetaType_ctor_function()’ member function declared in class ‘MyClass’
 Q_COREAPP_STARTUP_FUNCTION(MyClass::registerMetaType)
 ^
In file included from /path/to/qt5-5.6.0/include/QtCore/QtGlobal:1:0,
                 from /path/to/myclass.h:18,
                 from /path/to/myclass.cpp:15:
/path/to/myclass.cpp:183:1: error: qualified name does not name a class before ‘{’ token
 Q_COREAPP_STARTUP_FUNCTION(MyClass::registerMetaType)
 ^
/path/to/myclass.cpp:183:1: error: invalid type in declaration before ‘;’ token
 Q_COREAPP_STARTUP_FUNCTION(MyClass::registerMetaType)
 ^
/path/to/myclass.cpp:183:1: error: definition of ‘MyClass::registerMetaType_ctor_function_ctor_instance_’ is not in namespace enclosing ‘MyClass’ [-fpermissive]
/path/to/myclass.cpp:183:1: error: ‘static’ may not be used when defining (as opposed to declaring) a static data member [-fpermissive]
/path/to/myclass.cpp:183:1: error: ‘const int MyClass::registerMetaType_ctor_function_ctor_instance_’ is not a static member of ‘class MyClass’
/path/to/myclass.cpp:183:28: error: uninitialized const ‘MyClass::registerMetaType_ctor_function_ctor_instance_’ [-fpermissive]
 Q_COREAPP_STARTUP_FUNCTION(MyClass::registerMetaType)

Upvotes: 4

Views: 606

Answers (1)

Vincas Dargis
Vincas Dargis

Reputation: 555

I have reported feature request for Qt to add support for member functions: https://bugreports.qt.io/browse/QTBUG-66902

Looks like issue is with :: in static member function and usage of macros.

Anyway, alternative solution to overcome "polluting root namespace" and duplicate symbols, is to use namespaces:

namespace { // no duplicate symbol across units
namespace detail { // avoid "polluting" global namespace of this .cpp file

    void registerMetaTypes() {
        qRegisterMetaType(MyClass*);
    }

    Q_COREAPP_STARTUP_FUNCTION(registerMetaTypes)
} // namespace detail
} // anonymous namespace

Upvotes: 1

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