Re: [Boost-users] Must cast unsigned int for random generator seed

AMDG Phillip Jones wrote:

I wanted to save the initial state of a random number generator and I ran into this issue -

boost::mt19937 rng; unsigned int rseed = static_cast<unsigned int>(std::time(0)); //rng.seed( rseed ); // This causes an error rng.seed( static_cast<unsigned int>(rseed) ); // ok

The error is "mersenne_twister.hpp:103: error: `gen' cannot be used as a function".

Obviously not a big problem since I can just use the cast and keep going. But is there a reason for this behavior? It seems odd that one must cast an unsigned int as an unsigned int to make it work

This is definitely a bug. Please file a trac ticket at svn.boost.org. The following works. #include <ctime> #include int main() { boost::mt19937 rng; boost::mt19937::result_type rseed = static_castboost::mt19937::result_type(std::time(0)); rng.seed( rseed ); rng.seed( static_castboost::mt19937::result_type(rseed) ); } The problem is that seed is overloaded like so: void seed(UIntType value); template<class Generator> void seed(Generator & gen); (UUnitType is boost::unit32_t) If the argument is not exactly the same type that the mersenne_twister uses, then the second overload is a better match. Casting to an unsigned int works, because the second overload can never match an rvalue. In Christ, Steven Watanabe