If nmemb or size is 0, then calloc() returns either NULL, or a unique pointer value that can later be successfully passed to free(). If the multiplication of nmemb and size would result in integer overflow, then calloc() returns an error.

What does calloc return when it fails?

The calloc function allocates storage space for an array of num elements, each of length size bytes. ... calloc sets errno to ENOMEM if a memory allocation fails or if the amount of memory requested exceeds _HEAP_MAXREQ .

Does calloc set pointers to NULL?

Most frequently, calloc ing a structure with pointers: they are initialized to NULL.