QFile design

[redlars]

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?

[AcerExtensa]

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...

[lgeyer]

"What is the d-pointer":http://qt-project.org/wiki/Dpointer

[redlars]

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.

[andre]

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.