インプレイス処理で文字列を反転する

reverse.c

#include<stdio.h>
#define NULL_LENGTH 4

char* reverse(char* text){
	int i, length = sizeof text - NULL_LENGTH;
	for(i = length;i > (length / 2);i--){
		*(text+(i)) = *(text+(i)) ^ *(text+(length-i));
		*(text+(length-i)) = *(text+(i)) ^ *(text+(length-i));
		*(text+(i)) = *(text+(i)) ^ *(text+(length-i));
	}
	return text;
}

int main(){
	char st[10] = "abcde";
	char *s = st;
	printf("%s\n",s);
	printf("%s\n",reverse(s));
	return 0;
}