Question

Possible Duplicate:
Is it possible to modify a string of char in C?

#include <stdio.h>

void reverseStr(char *str);

main()
{
  reverseStr("abcdef");
}

void reverseStr(char *str) {
    char *tmp = str;
    char curr;
    while (*tmp != '\0') {
        tmp++;
    }
    tmp--;
    while (tmp > str) {
        curr = *str;
        *str = *tmp;
        *tmp = curr;
        str++;
        tmp--;
    }    
}

When I run it, I get:

/usr/bin/runit/srun_c: line 12:  2809 Segmentation fault      /tmp/run_c_executable

What on earth is going on? I’m practicing for an interview, I’m rusty in my C and wanted to practice something easy but can’t for the life of me figure this out.
I’ve noticed the seg fault disappears when I comment out the *str = *tmp; line, and I don’t see why that should cause a seg fault.
Help appreciated.

Answer 1

You can’t modify constant strings. Use a char array instead:

char str[] = "abcdef";

reverseStr(str);