Defined in header <functional>
template< class T >
struct not_equal_to;
(until C++14)
template< class T = void >
struct not_equal_to;
(since C++14)

Function object for performing comparisons. Unless specialised, invokes operator!= on type T.


The standard library provides a specialization of std::not_equal_to when T is not specified, which leaves the parameter types and return type to be deduced.

function object implementing x != y deducing argument and return types
(class template specialization)
(since C++14)

Member types

type definition
result_type(deprecated in C++17) bool
first_argument_type(deprecated in C++17) T
second_argument_type(deprecated in C++17) T

Member functions

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


bool operator()( const T& lhs, const T& rhs ) const;
(until C++14)
constexpr bool operator()( const T& lhs, const T& rhs ) const;
(since C++14)

Checks whether lhs is not equal to rhs.


lhs, rhs - values to compare

Return value

true if lhs != rhs, false otherwise.



Possible implementation

constexpr bool operator()(const T &lhs, const T &rhs) const 
    return lhs != rhs;

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