C++ is operator!= automatically provided when operator== defined

Question

I wonder if operator!= is automatically provided when operator== is defined within my class? When I have operator== defined in class A, obviously A a, A b, a == b works, but a != b doesn't. However I am not sure if it always happens. Are there any exceptions from this?

Answer 1

No, operators (apart from assignment) are never automatically generated. It's easy enough to define it in terms of ==:

bool operator!=(A const & l, A const & r) {return !(l == r);}

Answer 2

The operator != is not automatically provided for you. You may want to read about rel_ops namespace if you want such automation. Essentially you can say

using namespace std::rel_ops;

before using operator !=.