QApplication::desktop() incomplete type

I've done a new step - move to QT4

i try to port some old test apps and the next line of code:

Code:

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width=QApplication::desktop()->width();

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returns error while compiling

Code:

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error: invalid use of incomplete type ‘struct QDesktopWidget’

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i haven't noticed any diff between Qt3 and Qt4 docs.

did you include QDesktopWidget.h ?

No. thanks. it works.

I don't really understand why?
I'm using QApplication and its function. I thought it was enough to include QApplication?

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Originally Posted by codebehind

I'm using QApplication and its function. I thought it was enough to include QApplication?

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Read a bit about forward declarations.

http://www.parashift.com/c++-faq-lit...html#faq-39.11

thanks for the link jacek. It makes things a little more clear but still does not explain me why I could compile this code with qt3 and with qt4 i couldn't?
i've looked in qapplication.h and there is no forward declaration.

Quote:

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Originally Posted by codebehind

why I could compile this code with qt3 and with qt4 i couldn't?

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Because Qt4 sources are organised differently. Now the compiler must read QDesktopWidget code only when you really use it.

Quote:

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Originally Posted by codebehind

i've looked in qapplication.h and there is no forward declaration.

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Check again. Look near QT_MODULE macro.

Quote:

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Check again. Look near QT_MODULE macro.

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sorry. i was thinking about qt3 - qapplication.h

Quote:

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Originally Posted by codebehind

i was thinking about qt3 - qapplication.h

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In that case everything is OK. That's the difference between Qt3 and Qt4 --- Qt4 uses forward declaration.