Thread: Access Violation when writing to String

Why do I get an access violation when I try to change the value of individual characters in a char array via pointers?

If I pass a pointer-to-pointer-to-char (char **string) and try to change any of it's elements I get an access violation. This has happened with a few projects working with strings and I was never able to figure out why so I just ignored it, but now it's bugging me

So I'm attempting a recursive function to reverse a string in place and this is what I've got: I'll bold the line where I am getting an access violation.

Code:

#include <stdio.h>
#include "recursive.h"

char *buf;
int buf_p;

void reverse_string(void);

char *reverse(char **string){
	buf = *string;
	buf_p = 0;
	reverse_string();
	buf[buf_p] = '\0';
	return *string;
}

void reverse_string(){
	char c;
	if((c = buf[buf_p++]) != '\0')
		reverse_string();
	else{
		buf_p = 0;
		return;
	}
	buf[buf_p++] = c;
}