[Boost-users] Random number generation

I'm using the following code to generate a random 64 bit value: boost::mt19937 rng; boost::uniform_int<uint64_t> r(0,0xffffffffffffffff); boost::variate_generator<boost::mt19937&, boost::uniform_int<uint64_t> > gen(rng, r); uint64_t id = gen(); However it seems it's not random on each execution of the program? (rather I get the same value again). How do I randomise this properly?