Question

I am trying to understand how realloc works. This is my program. It’s giving some strange errors. Can anyone help me? I am just trying to do realloc for the array a. Any help appreciated.

#include<stdio.h>

int main()
{
    char a[5]="abcd";
    char *p;
    p = realloc(a,10);
    strcpy(a,"abcdefghi");
    printf("%s", a);
    return 0;
}

Answer 1

You must pass to realloc a pointer to memory allocated by malloc or one of its friends. In your code you are passing a which is a stack allocated variable.

Note that you cannot modify the size of stack allocated data so if your code does need to modify the size of a variable then that variable must be allocated on the heap.