210 bytes

#include<iostream>
#include<random>
#include<ctime>
#define L(a)for(int i=0;i<a;++i)std::cout<<f[rand()%16];
#define P(a)printf("-");L(a)
auto f="0123456789abcdef";void t(){srand(time(0));L(8)P(4)P(4)P(4)P(12)}