realloc() Function (Re Allocation Function)

realloc() Function (Re Allocation Function)         

Suppose previously allocated dynamic memory is not sufficient (or) memory is much larger than the requirement, in both cases some memory changes are required.  Memory changes can be done by using a library function called realloc() function.

           

realloc() function provides the altering the size of the memory allocation and the process is called reallocation of memory.  The general form of realloc() function is:

            Syntax:           ptrvariable = (casttype*)realloc(ptrvariable,newsize);

Where,

            ptrvariable is a pointer variable of type casttype.

Here,

            This function allocates a new memory space of the specified newsize and returns a pointer variable that represent first byte of the new memory block.  The newsize may be larger or smaller than the previous size.

Note:

             I.      The new memory block may or may not be begin at the same place as the old one.  In case, it is not able to find additional space in the same region, it will create the same in an entirely new region and moves the contents of the old block into the new block.

          II.      If the function is unsuccessful to allocate the memory space, it returns a NULL pointer and the original block is lost.

/* EXAMPLE PROGRAM FOR REALLOC() FUNCTION */

main()

{

            int *p,i,n;

            clrscr();

            printf("\nEnter how many numbers:");

            scanf("%d",&n);

            p=(int*)malloc(n*sizeof(int));

            p=(int*)realloc(p,(n+2)*sizeof(int));

            printf("\nEnter %d Elements:",n+2);

            for(i=0;i<n+2;i++)

            scanf("%d",p+i);

            printf("\nArray Elements Are:");

            for(i=0;i<n+2;i++)

            printf("      %d",*(p+i));

}