I just started using QT and noticed that all the example class definitions have the macro Q_OBJECT as the first line. What is the purpose of this preprocessor macro?
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1692answers:
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A:
From the Qt documentation:
The Meta-Object Compiler, moc, is the program that handles Qt's C++ extensions.
The moc tool reads a C++ header file. If it finds one or more class declarations that contain the Q_OBJECT macro, it produces a C++ source file containing the meta-object code for those classes. Among other things, meta-object code is required for the signals and slots mechanism, the run-time type information, and the dynamic property system.
Stu Mackellar
2009-09-02 16:23:24
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A:
It simply tells the pre-compiler that this class has gui elements and needs to be run through the 'moc' you only need to add this to classes that use the signal/slot mechanism.
But it will be quietly ignored in any other classes - it just adds to the build time.
Martin Beckett
2009-09-02 16:25:32
Minor nit-pick... a class doesn't have to have GUI elements to benefit from and/or need the Q_OBJECT macro. Basically, anything that inherits from QObject and needs access to the meta-data needs it. (Meta-data includes signals/slots.)
Caleb Huitt - cjhuitt
2009-09-02 23:04:02