##### 3.2.2.5 Allocating Cleared Space

The function `calloc` allocates memory and clears it to zero. It is declared in `stdlib.h`.

— Function: void * calloc (size_t count, size_t eltsize)

> This function allocates a block long enough to contain a vector of count elements, each of size eltsize. Its contents are cleared to zero before `calloc` returns.

You could define `calloc` as follows:

         void *
         calloc (size_t count, size_t eltsize)
         {
           size_t size = count * eltsize;
           void *value = malloc (size);
           if (value != 0)
             memset (value, 0, size);
           return value;
         }

But in general, it is not guaranteed that `calloc` calls `malloc` internally. Therefore, if an application provides its own `malloc`/`realloc`/`free` outside the C library, it should always define `calloc`, too.