Y is className a member function rather than a static one ?

[jacek]

Y have

Please, don't use such ugly abbreviations.

... declared className() as a member function rather than a static function ?

Because it wouldn't make sense. You need className() when you don't know the class name.

If className() was static, you would have to use it like this:

QString name( SomeClass::className() );

QString name( SomeClass::className() );

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Or you can write simply:

QString name( "SomeClass" );

QString name( "SomeClass" );

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The effect is the same and in either case you will have to change your code when you rename your class. The only difference, is that in former case you won't make a typo.

Now consider this:

BaseClass *base = new SomeClassDerivedFromBase();
qDebug() << base->className();

BaseClass *base = new SomeClassDerivedFromBase();
qDebug() << base->className();

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With inheritance mechanism, you can have a pointer that points to an instance of some class derived from a base class, but you not necessarily have to know which one and that's when you have to invoke className().