Access Violation I dont understand.

This is a discussion on Access Violation I dont understand. within the C++ Programming forums, part of the General Programming Boards category; The bold line below causes an access violation, I dont understand why... The second copy is what I did to ...

  1. #1
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    Access Violation I dont understand.

    The bold line below causes an access violation, I dont understand why... The second copy is what I did to fix it, can someone explain why the first one dosen't work?

    Code:
    	char* t = new char[10];
    	//load texture paths
    	for(int i = 0; i < 5; i++) {
    		//get the texture level by id
    		string texLevel = "TextureLevel";
    		texLevel += _itoa(i+1,t,10);
    		t = "      ";
    		temp->numTextures[i] = GetIntFromINI(texLevel,"Count",file,0);
    
    		//load all the paths on that level
    		for(int j = 0; j < temp->numTextures[i]; j++) {
    			string path = "Path";
    			path += _itoa(j+1,t,10);
    			t = "      ";
    			temp->textureList[i].push_front(new string(GetFromINI(texLevel,path,file,"")));
    		}
    	}
    	delete [] t;

    Code:
    	char* t;
    	//load texture paths
    	for(int i = 0; i < 5; i++) {
    		//get the texture level by id
    		string texLevel = "TextureLevel";
    		t = new char[10];
    		texLevel += _itoa(i+1,t,10);
    		delete [] t;
    		temp->numTextures[i] = GetIntFromINI(texLevel,"Count",file,0);
    
    		//load all the paths on that level
    		for(int j = 0; j < temp->numTextures[i]; j++) {
    			string path = "Path";
    			t = new char[10];
    			path += _itoa(j+1,t,10);
    			delete [] t;
    			temp->textureList[i].push_front(new string(GetFromINI(texLevel,path,file,"")));
    		}
    	}
    	delete [] t;

  2. #2
    Yes, my avatar is stolen anonytmouse's Avatar
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    Here you assign a constant string pointer to t:
    Code:
    			t = "      ";
    Here you try to write into that const string:
    Code:
    			path += _itoa(j+1,t,10);
    Here you try to delete that constant string pointer:
    Code:
    	delete [] t;
    If you want to copy a string into a char * buffer you must use strcpy():
    Code:
    strcpy(t, "      ");

  3. #3
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    I only had

    Code:
    t = "     ";
    because I was worried about overlapping numbers from the 'i' and 'j' using the same temporary array. 'i' will allways be a single digit, but 'j' could have multiple digits.

    I dont even think that is a problem with _itoa is it, im not sure. Am I making an sence? Its really late...

  4. #4
    & the hat of GPL slaying Thantos's Avatar
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    The problem is that your compiler marks the " " as read-only which means when itoa() tries to write to that memory location it causes a fault. Its not really a problem with one particular function or another as it is a side affect of the compiler marking it as read only. Most compilers I've seen do this but there are a couple that don't.

  5. #5
    and the hat of wrongness Salem's Avatar
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    You don't need to use new/delete - a simple
    char t[10];
    will suffice.

    Nor do you need to keep setting it to spaces each time around the loop.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  6. #6
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    I have allways considered it as though I was assigning a value, read-only never occured to me. Good to know, thanks.

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