Question

I am puzzled by this response.Can anyone help me on this and point out where I am making a mistake? The output at codepad is “memory clobbered before allocated block“

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(void)
{
    char *s = (char *)malloc(10 * sizeof(char));
    s = "heel";
    printf("%s\n",s);
    printf("%c\n",s[2]);
    printf("%p\n",s);
    printf("%d\n",s);
    free(s);
    return 0;
}

Answer 1

You’re trying to free constant memory with:

free(s); // cannot free constant "heel"

What you’re doing is allocating a piece of memory and storing its location (char *s). You are then overwriting that reference with one to a string constant “heel” (memory leak), which cannot be freed. To make this behave as desired, you should be copying the constant string to the memory you allocated:

strcpy(s, "heel");

---

Here is an example for getting user input:

char *input = malloc(sizeof(char) * 16); // enough space for 15 characters + '\0'
fgets(input, 16, stdin);

// do something with input

free(input);