C language inherently does not have any technique to allocate memory dynamically, there are 4 library functions under stdlib.h for dynamic memory allocation.

We already discuss about malloc() function in previous chapter.

calloc() function

calloc() is another memory allocation function that is used for allocating memory at runtime. calloc function is normally used for allocating memory to derived data types such as arrays and structures. If it fails to allocate enough space as specified, it returns a NULL pointer.

calloc() function is also like malloc() function. But calloc() initializes the allocated memory to zero. But, malloc() doesn’t.

Syntax:

The syntax of calloc() function is given below:

#include 
void *calloc(size_t num, size_t size);

ptr=(cast-type*)calloc(size_t num, size_t size);  // here ptr is a pointer

The calloc( ) function allocates memory the size of which is equal to num * size. That is, calloc( ) allocates sufficient memory for an array of num objects of size size. All bits in the allocated memory are initially set to zero.

Example

ptr = (float*) calloc(25, sizeof(float));

This statement allocates contiguous space in memory for an array of 25 elements each of size of float, i.e, 4 bytes.

free() function in C

The free( ) function returns the memory pointed to by ptr to the heap. This makes the memory available for future allocation.

The memory occupied by malloc() or calloc() functions must be released by calling free() function. Otherwise, it will consume memory until program exit.

Program; realloc() function and allocating address position

In this program, we are going to allcate some memory using calloc() function.

#include 
void free(void *ptr);

Program

In this program, we are going to allcate some memory using calloc() function.

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
 
int main()
{
     char *ptr;
     /* memory is allocated dynamically */
     ptr = calloc( 20, sizeof(char) );
     if( ptr== NULL )
     {
        printf("Couldn't able to allocate requested memory\n");
     }
     else
     {
         strcpy( ptr,"atnyla.com");
     }
         printf("Dynamically allocated memory content : " \
                "%s\n", ptr );
         free(ptr);
}

Dynamically allocated memory content : atnyla.com
Press any key to continue . . .

Program

In this program we are going to allcate some memory using calloc() function. From the user it will take some elements and it will give the smallest element.

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int i, n;
    int *ptr;

    printf("Enter total number of elements: ");
    scanf("%d", &n);

    ptr = (int*) calloc(n,sizeof(int));
	 /*returns a void pointer(which is type-casted to int*)
        pointing to the first block of the allocated space*/


//If it fails to allocate enough space as specified, it returns a NULL pointer.
    if(ptr == NULL)
    {
        printf("Error.Not enough space available");
        exit(0);
    }

    for(i=0;i<n;i++)
       scanf("%d",ptr+i); //storing elements from the user in the allocated space

    for(i=1;i<n;i++)
    {
       if(*ptr > *(ptr+i))
           *ptr = *(ptr+i);
    }

    printf("Smallest element is %d \n",*ptr);

    return 0;
}

Enter total number of elements: 5
2
3
7
1
8
Smallest element is 1
Press any key to continue . . .

Program

C program to find sum of n elements entered by user. To perform this program, allocate memory dynamically using calloc() function.

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int num, i, *ptr, sum = 0;
    printf("Enter number of elements: ");
    scanf("%d", &num);

	// Dynamic memory allocation
    ptr = (int*) calloc(num, sizeof(int));
    if(ptr == NULL)
    {
        printf("Error! memory not allocated.");
        exit(0);
    }

    printf("Enter elements of array: \n");
    for(i = 0; i < num; ++i)
    {
        scanf("%d", ptr + i); // takes element from user
        sum += *(ptr + i);
    }

    printf("Sum = %d \n", sum); // print sum
    free(ptr);
    return 0;
}

Enter number of elements: 5
Enter elements of array:
1
2
3
4
5
Sum = 15
Press any key to continue . . .

Difference Between malloc() and calloc()

int *ptr;
ptr = malloc( 20 * sizeof(int) );

int *ptr;
Ptr = calloc( 20, 20 * sizeof(int) );

 int *ptr;
ptr = (int*)malloc(sizeof(int)*20 );

 int *ptr;
ptr = (int*)calloc( 20, 20 * sizeof(int) );