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Array pointer deletion problem, Heap Corruption


i have a problem with deleting an array pointer:

char* compareBuffer = new char[patternSize];

This is how i create the array, patternSize is an int.
When i try to do delete[] compareBuffer; later on in the program, i get the following error reported:
Debug Error!
HEAP CORRUPTION DETECTED: after Normal block (#196) at 0x003694C8. CRT detected that the application wrote to memory after end of heap buffer.

Can someone explain what this means and how i can fix it? (If it is important, I'm using Visual Studio 2005)

Thank you.
1 Solution
Can we see some code, especially anything after the delete.  If I had to guess you are using your pointer after you delete it and it might not be obvious such as

delete[] compareBuffer;
*compareBuffer = 0; \\error
b3n_Author Commented:
This is the code:

bool findPattern()
            delete[] matchOffsets;
            matchOffsets = new int[256];
            char readChar;

            std::fstream fileReader;
            fileReader.open(fileName, std::ios::in | std::ios::binary);
                        fileReader.read(&readChar, sizeof readChar);

                        if((unsigned char)readChar == searchPattern[0]){

                              bool match = true;
                              char* compareBuffer = new char[patternSize];

                              fileReader.read(compareBuffer, sizeof compareBuffer);
                              for(int i = 0; i < patternSize; i++){
                                    match = (unsigned char)compareBuffer[i] == searchPattern[i];
                                    fileReader.seekg((int)fileReader.tellg() - patternSize + 1);
                              } else {
                                    int fileOffset = (int)fileReader.tellg() - patternSize;
                                    matchOffsets[matchCounter++] = fileOffset;
                              //Here comes the delete
                              delete[] compareBuffer;
            } else {
                  std::cout << "Error opening file";
                  return false;

            return true;
Is matchOffsets being initialized to NULL?

If it's not, this can give you a runtime error, since it's content's can be pointing to anything.

I recommend you use std::vector<char> instead of the above code.
std::vector is a safer way to create a dynamic array, and you don't have to worry about clean up via delete, because the array cleans up after itself.
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>> fileReader.read(compareBuffer, sizeof compareBuffer);

The above line of code is not correct.  the sizeof compareBuffer, will be the size of the pointer, and not the size of the allocated  buffer.
Should be the following:
fileReader.read(compareBuffer, patternSize);

>>matchOffsets = new int[256];
You should avoid using a dynamic array, if you need a small fixed size array.
Since the size of the above array is known at compile time, you can just declare a concrete variable.

int matchOffsets[256] = {0};

This is safer, and more efficient.
b3n_Author Commented:
its not about the matchOffsets its about the compare buffer. The rest of the code works fine, i just get problems when i try to delete the compareBuffer after i used it. And in the case of the compareBuffer i dont know how big it will be so i need to use dynamic arrays.
b3n_Author Commented:
i found the problem with this code snippet. the problem lies in this line:  fileReader.read(compareBuffer, sizeof compareBuffer); i shouldnt use sizeof comparebuffer, because it returns 4 while the actual buffer size is just 3.

thanks all for commenting on this question.
That is cause you have written beyond the allocated boundaries of the char array. If you allocate a char array in debug mode it is allocated some more space for the debugger. The debugger writes a signature at end which was checked at deletion. If you have written beyond boundaries the signature most likely was destroyed, hence the debug assertion.

Regards, Alex
>>i found the problem with this code snippet. the problem lies in this line:  fileReader.read(compareBuffer, sizeof compareBuffer); i shouldnt use sizeof
>>comparebuffer, because it returns 4 while the actual buffer size is just 3.

That's what I posted in my second comment.
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