Convert boost::uuid to char*

Just in case, there is also boost::uuids::to_string, that works as follows:

#include <boost/uuid/uuid.hpp>
#include <boost/uuid/uuid_io.hpp>

boost::uuids::uuid a = ...;
const std::string tmp = boost::uuids::to_string(a);
const char* value = tmp.c_str();