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Access violation in pointer arithmetic

With code:

int nsize;
int * buffer;
char TargetBuffer[4096];
const SIZE_T buffersize = (320*240) * sizeof(int);


buffer = (int *) malloc(bufferSize);
// fill buffer with data

nsize = 0;
while(nsize < buffersize)
{
    // HERE after some loops i get Access Violation
    memcpy(TargetBuffer, buffer + nsize, 4096);


    // do stuff with TargetBuffer
    nsize += 4096;
}

Why am I getting an access violation? What should I change?

+3


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3 answers


When you add buffer + nsize

, you have to understand what you are actually adding buffer + (nsize * (sizeof(int))

, as it int *

is when you do pointer arithmetic.



So it probably has something to do with it. Try increasing nsize by nsize += 4096/sizeof(int)

or something smarter.

+9


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I would do something like this:

SIZE_T left = buffersize;
nsize = 0;

while(left)
{
    SIZE_T block = (left >= 4096)?4096:left;
    // HERE after some loops i get Access Violation
    memcpy(TargetBuffer, buffer, block);
    buffer += (left) / sizeof(*buffer);

    // do stuff with TargetBuffer
    left -= block;
}


I'm sure the problem you are seeing is that you are going over the edge because your code doesn't care about dimensions that are not multiples of 4K.

+3


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Update the loop while

as

while(nsize < (buffersize/sizeof(int))

buffer

for int

, not char

. int

takes multiple bytes, you re-read and copy from memory that is not part buffer

.

0


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