Segmentation fault on array write

Question

I have just started learning C from Ritchie and Kernighan's book. I am trying to reverse a string recursively, however, I get a segmentation fault with this code:

#include <stdio.h>
#include <string.h>
void reverse (char s[], int l, int r);

int main () {
 
    reverse("hello world", 0, 10);
}
void reverse (char s[], int l, int r) {

    
    int temp = s[l];
    s[l] = s[r];
    s[r] = temp;
    
    if (++l >= --r) {
        return;
    } else {
        reverse (s, ++l, --r);
    }
   
}

I'm not sure what im doing wrong, but I found that the segmentation fault occurs at s[l] = s[r];

string literals (which you are passing as `s`) should not be written to. Treat them as read-only. Where do you expect the result to be stored anyway? — Eugene Sh., Aug 06 '20 at 22:02
btw, note that you are incrementing/decrementing `l` and `r` *twice* before the recursive call. I think it is not what you want to do. — Eugene Sh., Aug 06 '20 at 22:08

score 3 · Answer 1 · answered Aug 06 '20 at 22:03

3

The string you're passing to the function is a string constant. They are immutable, and attempting to change them is undefined behavior which is why it's crashing.

Create a local array to store the string, then pass that in.

int main () {
    char str[] = "hello world";
    reverse(str, 0, 10);
}

answered Aug 06 '20 at 22:03

dbush

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ah thanks, im an idiot lol – Ethan Suresh Aug 06 '20 at 22:04
String literals aren't constants (nor are they `const`-qualified) – M.M Aug 06 '20 at 22:23

Segmentation fault on array write

1 Answers1