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List:       kde-devel
Subject:    Strange backtrace
From:       Stefan Majewsky <majewsky () gmx ! net>
Date:       2009-07-28 19:48:08
Message-ID: 200907282148.11756.majewsky () gmx ! net
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Hi,

during my last refactoring, I've introduced some crashes in Kolf 2, which I'm 
working through currently. While analysing a backtrace, I stumbled upon 
something that puzzled me, and contradicts my understanding of C++. As it 
might be that this misunderstanding hinders me from discovering the true 
source of the crash, I thought it might be good to ask for help here. Here is 
the relevant part of the backtrace:

> Application: Kolf (kolf-ng), signal: Segmentation fault
> [KCrash Handler]
> #6  0x00000000 in ?? ()
> #7  0x0808f277 in Kolf::Game::setCurrentHole (this=0xbfb99b78, newHole=0)
> at /home/smajewsky/Code/kolf/kolf/engine/game.cpp:109
> #8  0x08093a56 in Kolf::NormalGame::startGame (this=0x82097e8)
> at /home/smajewsky/Code/kolf/kolf/engine/game-normal.cpp:77
> #9  0x080966a4 in Kolf::MainWindowPrivate::newGame (this=0x81e50a8)
> at /home/smajewsky/Code/kolf/kolf/intßerface/mainwindow.cpp:87

And here's a code sample from the Kolf::NormalGame class, a subclass of 
Kolf::Game: (The full code is in playground/games/kolf-ng/engine.)

bool Kolf::NormalGame::startGame()
{
	if (players().count() == 0 || course()->holeCount() <= 0)
		return false;
	gameUI()->setWindowTitle(course()->title());
	//start with first hole and first player
	setCurrentHole(0); /* This is line 77 */
	return true;
}

As you see, the second-to-last line in the method invokes 
Kolf::Game::setCurrentHole, which equals the step from #8 to #7 in above 
backtrace. The fact that puzzles me is that the this pointer changes between 
#8 and #7. How can I interpret this? In my understanding the this pointer 
stays the same even during casts (if we disregard multiple inheritance which 
is not used in this class layout). Is this wrong?

Thanks for any help.

Greetings
Stefan

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