Difference between malloc and calloc?

Question

What is the difference between doing:

ptr = (char **) malloc (MAXELEMS * sizeof(char *));

or:

ptr = (char **) calloc (MAXEL         


        

Answer 1

One often-overlooked advantage of calloc is that (conformant implementations of) it will help protect you against integer overflow vulnerabilities. Compare:

size_t count = get_int32(file);
struct foo *bar = malloc(count * sizeof *bar);

vs.

size_t count = get_int32(file);
struct foo *bar = calloc(count, sizeof *bar);

The former could result in a tiny allocation and subsequent buffer overflows, if count is greater than SIZE_MAX/sizeof *bar. The latter will automatically fail in this case since an object that large cannot be created.

Of course you may have to be on the lookout for non-conformant implementations which simply ignore the possibility of overflow... If this is a concern on platforms you target, you'll have to do a manual test for overflow anyway.