calloc():

• calloc() stands for contiguous allocation and is also used for allocating a specified number of bytes, given by the number of bytes to allocate and the size of each such object in bytes.
• It is normally used for allocating memory to derived data types such as arrays and structures.
• In the case of calloc() the memory allocated is initialized to 0 unlike malloc() where memory is left uninitialized(garbage values).
• The pointer returned is of type void hence we can typecast such pointer to any type as per to need.
• It returns NULL in case memory is not allocated for some reason.

Syntax:

(void*) calloc (size_t n , size_t size);

Where ‘n’ is the number of blocks to be allocated and size_t is the size of each block(size of each element).

Hence the total number of bytes allocated is (n * size).

Example:

int *ptr = (int*) calloc( 5 , sizeof(int));

The above example allocates a total of 5 blocks where the size of each block is that of type int.

Calloc to allocate memory for structure

#include <stdlib.h>
#include <string.h>

struct Student
{
  char *name;
  int roll;
  float marks;
};

int main ()
{
  struct Student *stud = (struct Student *)calloc (30, sizeof(struct Student));
  if (stud == NULL)
     printf("\n Memory allocation failed\n");
   else
   {
      stud->roll = 20;
      stud->name="techaccess";
      stud->marks = 2345.7;
     printf("\n Name: %s roll: %d marks is: %f \n", stud->name, stud->roll, stud->marks);
   }
   return 0;
 }

Output:

Name: techaccess roll no: 20 marks is: 2345.699951

Application:

Database applications, for instance, will have such a requirement. Proper planning for the values of “n” and “size” can lead to good memory utilization. This is a uniform block of memory of a specific size is achieved with calloc().

Drawback: Size cannot be changed.

Relevant Posts:

• Dynamic Memory Allocation
• malloc()
• realloc()
• free()
• Memory Allocators: brk() and sbrk()
• User defined malloc(), calloc(), realloc() and free()
• Interview questions on dynamic memory allocation

Categories: C Language