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this pointer troubles

General and Gameplay Programming Programming

Started by mstein March 23, 2003 03:51 PM

5 comments, last by mstein 21 years, 1 month ago

mstein

122

Author

March 23, 2003 03:51 PM

Okay, i have the following code:

  
if(myMove.empty()) {
			this->animating = false;
			this->myMove.clear();
			CC_Piece * tempThis = this;
			this->endCell->setPiece(tempThis);
		}

When i run the program, the first line in setPiece(CC_Piece *) crashes. I assume it has something to do with my calling the setPiece function and passing it the "this" pointer. Here is where it crashes:

  
void CC_Cell::setPiece(CC_Piece * pPiece) {
	this->cellPiece = pPiece;
	this->cellPiece->setWindowX(this->mWindowX);
	this->cellPiece->setWindowY(this->mWindowY);
}

any help???

JohnBolton

1,373

March 23, 2003 04:10 PM

My first suggestion is to get rid of all the "this->". They are never needed and they just clutter up the code (unless you are trying to do C++ stuff with a C compiler). If you think they are needed, then you are doing something wrong.

As far as your crash... it crashes, oh joy.

(sorry for the whining)

Why do some people think that other people have fully-featured development systems embedded in their brains? How can anyone possibly know the answer to "why doesn''t this compile"? "why doesn''t this link?", "why doesn''t this work?", and "why does this crash?", when all that is provided is a couple lines of source code????

At least provide the error message!!! At least describe what it is supposed to do, and what it is doing or not doing!!!!
...

My GUESS is that "endCell" is 0, so when you call setPiece(), "this" is 0.

John BoltonLocomotive Games (THQ)Current Project: Destroy All Humans (Wii). IN STORES NOW!

mstein

122

Author

March 23, 2003 04:19 PM

1) I know they are not needed, its personal preference i guess and I''m pretty sure it doesnt affect performance.
2) The error message is:

quote:
Unhandled exception at 0x00455329 in Chinese Checkers.exe: 0xC0000005: Access violation writing location 0xfdfdfdfd.

0xfdfdfdfd is the address of endCell in the source below. It is not set to 0. My main question is has anyone ever had problems passing the "this" pointer to a member of a class. That is what seems to be the problem. When I do not use the this pointer it works ( i use this function elsewhere in the code ) . . . sorry to assume that everyone has a fully featured development system embedded in their head. Any help is appreciated.

Beer Hunter

712

March 23, 2003 04:29 PM

quote:Unhandled exception at 0x00455329 in Chinese Checkers.exe: 0xC0000005: Access violation writing location 0xfdfdfdfd.

endCell wasn''t initialised.

billybob

134

March 23, 2003 04:30 PM

looks like a debugger initialized pointer. do you realize what the this pointer is?

AClass * Testing = (AClass*)0x12345678;Testing->AMethod { this == 0x12345678; /* true */ }

you don't need to put this-> in front of everything, the compiler does that automatically. there is ZERO difference between what you did and if you don't have this-> on everything. all it does is clutter. somewhere, you aren't intialializing a pointer. basically, you created a pointer somewhere like this:

CC_Cell * ACell;

the debugger, since you didn't set this to any value specifically, sets this to its debug value, in your case 0xFDFDFDFD. if you happened to replace that line with CC_Cell * ACell = 0;, you would get the same error but 'Access violation writing location 0x00000000'

[edited by - billybob on March 23, 2003 5:30:42 PM]

mstein

122

Author

March 23, 2003 04:47 PM

thank you for your help, turns out i was grabbing the pointer to a CC_Cell object from a vector i was using to store CC_Cell*''s. Problem was that there is one case where the vector would get emptied before I grabbed the pointer . . . then when i called vector::back, it was returning something useless.

thanks again, and again i realize that the "this" pointer is not needed . . . guess i should go through and take it out, it doesnt bother me though.

JohnBolton

1,373

March 23, 2003 11:28 PM

quote:Original post by mstein
My main question is has anyone ever had problems passing the "this" pointer to a member of a class.

"this" is not really any different from any other pointer. However, you probably want to avoid doing this:

delete this;

John BoltonLocomotive Games (THQ)Current Project: Destroy All Humans (Wii). IN STORES NOW!

this pointer troubles

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