Re: [Boost-users] Small logic::tribool riddle

On Fri, Mar 11, 2011 at 11:53 AM, Thomas Jarosch < thomas.jarosch@intra2net.com> wrote:

Hello,

here's a small boost::logic::tribool riddle:

-<snip>-------------------------------------

#include <iostream> #include

int main(void) { boost::logic::tribool foo(boost::logic::indeterminate); if (foo != true) { std::cout << "reached1\n"; }

if (foo == boost::logic::indeterminate) { std::cout << "reached2\n"; }

return 0; }

-<snap>-------------------------------------

Try to determine the printed result without looking at the boost::logic::tribool implementation / documentation.

Intuitive?

Ok, I guessed, got it wrong, read the docs, and still don't get it! Modifying your example to... #include <iostream> #include int main(void) { boost::logic::tribool foo(boost::logic::indeterminate); if (foo != true) { std::cout << "reached1\n"; } if (foo == boost::logic::indeterminate) { std::cout << "reached2\n"; } if (boost::logic::indeterminate == boost::logic::indeterminate) { std::cout << "reached3\n"; } return 0; } only prints "reached3", so I can see the logic of second test being indeterminate rather than true, but then surely the comparing indeterminate with indeterminate should also be true? Weird! - Rob.