C realloc() function

C realloc() function - Reallocate memory blocks

Syntax realloc() function

void *realloc(void *ptr, size_t size)

The realloc() function is used to change the size of a previously reserved storage block. The ptr argument points to the beginning of the block. The size argument gives the new size of the block, in bytes.

If the ptr is NULL, realloc() reserves a block of storage of size bytes. It does not necessarily give all bits of each element an initial value of 0.

If size is 0 and the ptr is not NULL, realloc()frees the storage allocated to ptr and returns NULL

Parameters realloc() function

Name Description Required /Optional
ptr Pointer to previously allocated memory block. Required
size New size in bytes. Required

Return value from realloc()

  • Returns a pointer to the newly allocated memory.
  • If size is 0, the realloc() function returns NULL.

Example: realloc() function

The following example shows the usage of realloc() function.

//To use realloc in our program

int main()
    int *ptr,i;

    //allocating memory 
    ptr = malloc(sizeof(int));
    ptr[0] = 10;
    ptr[1] = 20;
    //realloc memory size  
    ptr = realloc(ptr, 3 * sizeof(int));
    ptr[2] = 300;
    ptr[3] = 400;
    ptr[4] = 500;
    //printing values
    for(i = 0; i <= 4; i++)

    return 0;



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