The calloc(3) API is almost identical to malloc(3), differing in two main respects:

• It initializes the memory chunk it allocates to the zero value (that is, ASCII 0 or NULL, not the number 0)
• It accepts two parameters, not one

The calloc(3) function signature is as follows:

 void *calloc(size_t nmemb, size_t size);

The first parameter, nmemb, is n members; the second parameter, size, is the size of each member. In effect, calloc(3) allocates a memory chunk of (nmemb*size) bytes. So, if you want to allocate memory for an array of, say, 1,000 integers, you can do so like this:

    int *ptr;
    ptr = calloc(1000, sizeof(int));

Assuming the size of an integer is 4 bytes, we would have allocated a total of (1000*4) = 4000 bytes.

Whenever one requires memory for an array of items (a frequent use case in applications is an array of structures), calloc is a convenient way to both allocate and simultaneously initialize the memory.