Question

I have a simple program, for learning purposes, yet I keep on getting null returned when I realloc from allocated array.

#include <stdio.h>

#include <stdlib.h>


void main() 
{
    char *ptr, *retval;

    ptr = (char *)calloc(10, sizeof(char));

    if (ptr == NULL)
        printf("calloc failed\n");
    else
        printf("calloc successful\n");

    retval = (char *)realloc(ptr, 5);

    if (retval == NULL)
        printf("realloc failed\n");    
    else
        printf("realloc successful\n");

    free(ptr);
    free(retval);

}

I’m not able to realloc, retval = (char *)realloc(ptr, 5);
what am I doing wrong?

Answer 1

It works as expected for me:

calloc successful
realloc successful
*** glibc detected *** double free or corruption

The code looks fine, assuming the double free was intentional. Don’t call free(ptr) since you’ve already released it by reallocating it.