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std::ranges::not_equal_to(3) C++ Standard Libary std::ranges::not_equal_to(3)


std::ranges::not_equal_to - std::ranges::not_equal_to


Defined in header <functional>
struct not_equal_to; (since C++20)

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

Member types

Member type Definition
is_transparent /* unspecified */

Member functions

operator() checks if the arguments are not equal
(public member function)


template< class T, class U >

requires std::equality_comparable_with<T, U> // with different sematic

constexpr bool operator()(T&& t, U&& u) const;

Compares t and u. Equivalent to return !ranges::equal_to{}(std::forward<T>(t),


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.


This section is incomplete
Reason: no example

Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG 3530 C++20 syntactic checks were relaxed while only semantic requirements
comparing pointers relaxed

See also

not_equal_to function object implementing x != y
(class template)