C <stdlib.h> - calloc() Function

The C <stdlib.h> calloc() function is used to allocate a block of memory for an array of num elements of size bytes long, and initializes all its bits to zero. If allocation succeeds, it returns a pointer to the lowest (first) byte of newly allocated memory.

If size is zero, the behavior of the function is implementation-defined (it may or may not be a null pointer), but the returned pointer shall not be dereferenced, and should be passed to free() to avoid memory leaks.

Syntax

void* calloc (size_t num, size_t size);

Parameters

Return Value

On success, returns a pointer to the lowest (first) byte of newly allocated memory. The type of this pointer is always void*, which can be cast to the desired type of data pointer in order to be dereferenceable. On failure, returns a null pointer.

Example:

The example below shows the usage of <stdlib.h> calloc() function.

#include <stdio.h>
#include <stdlib.h>
 
int main (){
  //allocating memory for array of 5 int
  int *p1 = (int*) calloc(5, sizeof(int)); 
  
  //another way of doing the same
  int *p2 = (int*) calloc(1, sizeof(int[5]));

  //another way of doing the same
  int *p3 = (int*) calloc(5, sizeof *p3);

  //displaying the array
  for(int i=0; i<5; i++)
	printf("p1[%d] = %d\n", i, p1[i]);

  //deallocating previously allocated memory
  free(p1);
  free(p2);
  free(p3);
  return 0;
}

The output of the above code will be:

p1[0] = 0
p1[1] = 0
p1[2] = 0
p1[3] = 0
p1[4] = 0