Passing pointers with space allocated by malloc

I've just written a function that returns a pointer to a block of memory allocated by malloc. If I call free() on the returned pointer, will this free the memory?

I tried reading up on this, but I can't find anything that says whether you can call a different pointer pointing to the same location and whether that will free all the memory or not.

This is probably majorly basic, I think I can't find the info 开发者_C百科because I'm searching for it wrong.

Any help appreciated!

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Yes calling free will free the memory. Its not the pointer that get freed but the memory that the pointer points to that is freed.

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You must pass to free() the value obtained from malloc().

int *x = malloc(42 * sizeof *x);
int *p = &x[0];
free(p);                /* ok, same as free x; x and p have the same value */

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Edit: another example

int *x = malloc(42 * sizeof *x);
for (k = 0; k < 24; k++) *x++ = 0; /* zero first 24 elements */
free(x - 24);

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It's not entirely clear what you're asking here, but if what you're asking is:

Can I call free() on a pointer which points to a location within the allocated block?

then the answer is "no" -- you must pass free() the exact pointer which you got back from malloc(). Trying to free() an internal pointer, or a pointer to memory which was not allocated by malloc(), memory corruption or a crash are likely to occur.