boost::logic::operator!= — 比较 tribool 是否不相等。
// In header: <boost/logic/tribool.hpp> BOOST_CONSTEXPR tribool operator!=(tribool x, tribool y); BOOST_CONSTEXPR tribool operator!=(tribool x, bool y); BOOST_CONSTEXPR tribool operator!=(bool x, tribool y); BOOST_CONSTEXPR tribool operator!=(indeterminate_keyword_t, tribool x); BOOST_CONSTEXPR tribool operator!=(tribool x, indeterminate_keyword_t);