Reverse a string in C without using temporary storage

reverse.c

#include <string.h>

void reverse(char* str) {
    
    int i;
    int len = strlen(str);
    for (i = 0; i < len/2 ; ++i){
        str[len] = str[i];
        str[i] = str[len - i - 1];
        str[len - i - 1] = str[len];
    }
    str[len] = '\0';
}

int main() {
    char str[] = "A string";
    printf("String: \"%s\"\n", str);
    reverse(str);
    printf("And its reverse: \"%s\"\n", str);
}