memcpy(), what should the value of the size parameter be?

Question

I want to copy an int array to another int array. They use the same define for length so they\'ll always be of the same length.

What are the pros/cons of the followi

Answer 1

If dst was allocated from the heap (using malloc for example) the second solution will not work. sizeof(dst) will only work when it is know to the compiler. For example, the following example will fail as sizeof(dst) will be equal to the sizeof a pointer (4-8 bytes.)

#define ARRAY_LENGTH 10
int *dst;

dst = malloc(ARRAY_LENGTH*sizeof(int));
memcpy(dst, src, sizeof(dst)); // sizeof dst in this case would be 4 bytes on 32 bit system

This code segment will work every time:

#define ARRAY_LENGTH 10
int *dst;

dst = malloc(ARRAY_LENGTH*sizeof(int));
memcpy(dst, src, ARRAY_LENGTH*sizeof(int)); // sizeof would be 40 bytes