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The GNU C Library

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.