boost tribool
boost::logic::tribool is similar to bool. However, while bool can distinguish two states, boost::logic::tribool handles three.
#include <boost/logic/tribool.hpp> #include <boost/logic/tribool_io.hpp> #include <iostream> using namespace boost::logic; int main() { std::cout.setf(std::ios::boolalpha); tribool b1 = true; std::cout << (b1 || indeterminate) << std::endl; std::cout << (b1 && indeterminate) << std::endl; tribool b2 = false; std::cout << (b2 || indeterminate) << std::endl; std::cout << (b2 && indeterminate) << std::endl; tribool b3 = indeterminate; std::cout << (b3 || b3) << std::endl; std::cout << (b3 && b3) << std::endl; return 0; }
输出为:
true
indeterminate
indeterminate
false
indeterminate
indeterminate
You can use logical operators with variables of type boost::logic::tribool, just as you can with variables of type bool. In fact, this is only way to process variables of type boost::logic::tribool because the class dosen't provide any member functions.