UUID RFC 4122 Version 4 (random) generator

uuid.c

// UUID RFC 4122 Version 4 (random)

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
​
void random_chars(char buffer[], int len) {
    for (int i = 0; i < len; i++) {
        sprintf(buffer + i, "%X", rand() % 16);
    }
}
​
char* uuid4(char buffer[33]) {
    char* c = buffer;
    int i = 0;
    random_chars(buffer + i, 8);
    i+=8;
    buffer[i++] = '-';
    random_chars(buffer + i, 4);
    i+=4;
    buffer[i++] = '-';
    buffer[i++] = '4';  // uuid version (0b0100)
    random_chars(buffer + i, 3);
    i+=3;
    buffer[i++] = '-';
    buffer[i++] = "89AB"[rand() % 4];  // uuid variant (0b10??)
    random_chars(buffer + i, 3);
    i+=3;
    buffer[i++] = '-';
    random_chars(buffer + i, 12);
    i+=12;
    buffer[i++] = 0;
    return buffer;
}
​
int main(int argc, char* argv[]) {
    srand(time(NULL));
    char buffer[32];
    printf("%s", uuid4(buffer));
    printf("\n");
    return 0;
}