Write a C Program to understand the use of realloc() function

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C realloc()

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If the previously allocated memory is insufficient or more than required, you can change the previously allocated memory size using realloc().

Description

The C library function void *realloc(void *ptr, size_t size) attempts to resize the memory block pointed to by ptr that was previously allocated with a call to malloc or calloc.

Syntax of realloc() : :

ptr = realloc(ptr, size);

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Parameters

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• ptr — This is the pointer to a memory block previously allocated with malloc, calloc or realloc to be reallocated. If this is NULL, a new block is allocated and a pointer to it is returned by the function.
• size — This is the new size for the memory block, in bytes. If it is 0 and ptr points to an existing block of memory, the memory block pointed by ptr is deallocated and a NULL pointer is returned.

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Return Value

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This function returns a pointer to the newly allocated memory, or NULL if the request fails.

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Below is the source code for C Program to understand the use of realloc() function which is successfully compiled and run on Windows System to produce desired output as shown below :

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SOURCE CODE : :

/* Program to understand the use of realloc() function*/

#include<stdio.h>
#include<stdlib.h>
int main( )
{
        int i, *ptr;
        ptr = (int *)malloc(5 *sizeof(int));
        if(ptr == NULL)
        {
                printf("Memory not available\n");
                exit(1);
        }
        printf("Enter 5 integers : ");
        for(i=0; i<5; i++)
                scanf("%d", ptr+i);
        /*Allocate memory for 4 more integers*/
        ptr = (int *)realloc(ptr, 9*sizeof(int));
        if(ptr == NULL)
        {
                printf("Memory not available\n");
                exit(1);
        }
        printf("Enter 4 more integers : ");
        for(i=5; i<9; i++)
                scanf("%d", ptr+i);
        for(i=0; i<9; i++)
                printf("%d ", *(ptr+i));
}

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OUTPUT ::

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//OUTPUT ::


Enter 5 integers : 6
3
4
5
9
Enter 4 more integers : 7
0
1
1
6 3 4 5 9 7 0 1 1

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