QFile design
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Using Qt 4.7.1
Looking at the QFile implementation it appears that all member variables are stored in a class QFilePrivate which does not provide any form of encapsulation.
What benefit does the separation of methods and variables provide? Is this a design pattern?
To access the instance of QFilePrivate the QFile uses the "d" pointer. An example "d->fileName.IsEmpty()". Where is the pointer "d" defined?
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It is mostly the case in Qt framework with private classes. It is just to make end class look pretty for developers. pointer *d is always defined in private section of its end class. The private class itself is predefined in header, right before end class.
@class QFilePrivate;@
and declared in .cpp file.
or just in separate private header and source files which you can find under src/ folder and not in include/ folder.It is actually nice design pattern, helps make code clear in big projects and hide simple and conventional code which will mostly never changed in separate classes...
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"What is the d-pointer":http://qt-project.org/wiki/Dpointer
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Thought "this":http://zchydem.enume.net/2010/01/19/qt-howto-private-classes-and-d-pointers/ and "this":http://techbase.kde.org/Policies/Binary_Compatibility_Issues_With_C++#Definition article described the issue nicely.
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Actually, it provides very strong encapsulation. You cannot access the d pointer as a user of the API, which is the whole point of encapsulation.
