How allocate or free only parts of an array?

Question

See this example:

int *array = malloc (10 * sizeof(int))

Is there a way to free only the first 3 blocks?

Or to have an array with n

Answer 1

You can't free part of an array - you can only free() a pointer that you got from malloc() and when you do that, you'll free all of the allocation you asked for.

As far as negative or non-zero-based indices, you can do whatever you want with the pointer when you get it back from malloc(). For example:

int *array = malloc(10 * sizeof(int));
array -= 2;

Makes an array that has valid indices 2-11. For negative indices:

int *array = malloc(10 * sizeof(int));
array += 10;

Now you can access this array like array[-1], array[-4], etc.

Be sure not to access memory outside your array. This sort of funny business is usually frowned upon in C programs and by C programmers.