c - Difference between malloc and calloc?

What is the difference between doing:

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

or:

ptr = (char **) calloc (MAXELEMS, sizeof(char*));

When is it a good idea to use calloc over malloc or vice versa?

Answer

calloc() zero-initializes the buffer, while malloc() leaves the memory uninitialized.

EDIT:

Zeroing out the memory may take a little time, so you probably want to use malloc() if that performance is an issue. If initializing the memory is more important, use calloc(). For example, calloc() might save you a call to memset().