Question

When overloading operators, is it necessary to overload >= <= and !=?

It seems like it would be smart for c++ to call !operator= for !=, !> for operator<= and !< for operator>=.

Is that the case, or is it necessary to overload every function?

Answer 1

Yes, it is necessary, if you want all of them to work the way you want them to work.

C++ does not force any specific semantics on most of the overloadable operators. The only thing that is fixed is the general syntax for the operator (including being unary or binary and things like precedence and associativity). This immediately means that the actual functionality that you implement in your overload can be absolutely arbitrary. In general case there might not be any meaningful connection between what operator == does and what operator != does. Operator == might write data to a file, while operator != might sort an array.

While overloading operators in such an arbitrary fashion is certainly not a good programming practice, the C++ language cannot assume anything. So, no, it cannot and will not automatically use ! == combination in place of !=, or ! > combination in place of <=.