Question

I am learning how to use pointers, so i wrote the below program to assign integer values in the interval [1,100] to some random locations in the memory.

When i read those memory locations, printf displays all the values and then gives me a segmentation fault. This seems an odd behavior, because i was hoping to see either all the values OR a seg fault, but not both at the same time.

Can someone please explain why i got to see both?

Thanks. Here is the code

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

int main()
{
    char first = 'f';
    char *ptr_first = &first;
    int i=1;
    for(i=1;i<101;i++)
        *(ptr_first+i) = i;
    for(i=1;i<101;i++)
        printf("%d\n", *(ptr_first+i));
    return EXIT_SUCCESS;
} 

Answer 1

Not odd at all. You are using your variable first, which is on the stack. What you essentially do is happily overwriting the stack (otherwise known from buffer overflows on the stack) and thus probably destroying any return address and so on.

Since main is called by the libc, the return to libc would cause the crash.