Ordering of boolean values

Question

Under C++ or from C99, how is the less-than operator < defined for boolean values?

Alternatively, explain the behaviour of

Answer 1

Boolean values are ordered such that false is smaller than true. According to the standard, a bool can only hold two values: true and false, so the conversions in (bool)-1 should have yielded true (as all non-0 values when converted to bool are true). That is the behavior in clang and g++-4.7.

The actual comparison (I believe) is done on int after the bool is promoted, and it seems that the compilers you tested avoided the intermediate step of converting through bool and just promoted the actual bool value.