std::ranges::not_equal_to

struct not_equal_to;

Function object for performing comparisons. Deduces the parameter types of the function call operator from the arguments (but not the return type).

Implementation-defined strict total order over pointers

The function call operator yields the implementation-defined strict total order over pointers if the = operator between arguments invokes a built-in comparison operator for a pointer, even if the built-in = operator does not.

The implementation-defined strict total order is consistent with the partial order imposed by built-in comparison operators (<=>, <, >, <=, and >=), and consistent among following standard function objects:

• std::less, std::greater, std::less_equal, and std::greater_equal, when the template argument is a pointer type or void
• std::ranges::equal_to, std::ranges::not_equal_to, std::ranges::less, std::ranges::greater, std::ranges::less_equal, std::ranges::greater_equal, and std::compare_three_way

Member types

Member functions

template< class T, class U >
    requires std::equality_comparable_with<T, U> // with different sematic requirements
constexpr bool operator()(T&& t, U&& u) const;

Notes

Unlike std::not_equal_to, std::ranges::not_equal_to requires both == and != to be valid (via the equality_comparable_with constraint), and is entirely defined in terms of std::ranges::equal_to.

Example

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also