getting the size of allocated space

Given the following code:

Code:

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int *p = malloc(sizeof(int) * 20);

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If I had no idea how much space was allocated, how would I get the size of the space that the pointer p is pointing to (which would be 80 in this case)?

Use real variables for size instead of magic numbers.

It's platform specific (see MSDN for windows, I don't know how to do it on linux). I suggest you keep track if it yourself though.

For example:

Code:

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size_t pSize = 0;
int * p = NULL;

pSize = 20 * sizeof(int);
p = malloc(pSize);

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Quote:

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If I had no idea how much space was allocated

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How is that possible? You know how much space was allocated because you know what you passed to malloc.