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std::binary_negate - cppreference.com

template< class Predicate > struct binary_negate : public std::binary_function< Predicate::first_argument_type, Predicate::second_argument_type, bool >; (until C++11)

template< class Predicate > struct binary_negate;

(since C++11)
(deprecated in C++17)
(removed in C++20)

std::binary_negate is a wrapper function object returning the complement of the binary predicate it holds.

The binary predicate type must define two member types, first_argument_type and second_argument_type, that are convertible to the predicate's parameter types. The function objects obtained from std::owner_less, std::ref, std::cref, std::plus, std::minus, std::multiplies, std::divides, std::modulus, std::equal_to, std::not_equal_to, std::greater, std::less, std::greater_equal, std::less_equal, std::logical_not, std::logical_or, std::bit_and, std::bit_or, std::bit_xor, std::mem_fn, std::map::value_comp, std::multimap::value_comp, std::function, or from a call to std::not2 have these types defined, as are function objects derived from the deprecated std::binary_function.

std::binary_negate objects are easily constructed with helper function std::not2.

[edit] Member types Type Definition first_argument_type Predicate::first_argument_type second_argument_type Predicate::second_argument_type result_type bool [edit] Member functions constructs a new binary_negate object with the supplied predicate
(public member function) returns the logical complement of the result of a call to the stored predicate
(public member function) std::binary_negate::binary_negate

explicit binary_negate( Predicate const& pred );

(until C++14)

constexpr explicit binary_negate( Predicate const& pred );

(since C++14)

Constructs a std::binary_negate function object with the stored predicate pred.

Parameters pred - predicate function object std::binary_negate::operator()

bool operator()( first_argument_type const& x, second_argument_type const& y ) const;

(until C++14)

constexpr bool operator()( first_argument_type const& x, second_argument_type const& y ) const;

(since C++14)

Returns the logical complement of the result of calling pred(x, y).

Parameters x - first argument to pass through to predicate y - second argument to pass through to predicate Return value

The logical complement of the result of calling pred(x, y).

[edit] Example

#include <algorithm>
#include <cstddef>
#include <functional>
#include <iostream>
#include <vector>
 
struct same : std::binary_function<int, int, bool>
{
    bool operator()(int a, int b) const { return a == b; }
};
 
int main()
{
    std::vector<int> v1;
    for (int i = 0; i < 7; ++i)
        v1.push_back(i);
 
    std::vector<int> v2(v1.size());
    std::reverse_copy(v1.begin(), v1.end(), v2.begin());
 
    std::vector<bool> v3(v1.size());
 
    std::binary_negate<same> not_same((same()));
 
    // C++11 solution:
    // std::function<bool (int, int)> not_same =
    //     [](int x, int y) -> bool { return !same()(x, y); };
 
    std::transform(v1.begin(), v1.end(), v2.begin(), v3.begin(), not_same);
 
    std::cout.setf(std::ios_base::boolalpha);
    for (std::size_t i = 0; i != v1.size(); ++i)
        std::cout << v1[i] << " != " << v2[i] << " : " << v3[i] << '\n';
}

Output:

0 != 6 : true
1 != 5 : true
2 != 4 : true
3 != 3 : false
4 != 2 : true
5 != 1 : true
6 != 0 : true

[edit] See also

(deprecated in C++11)(removed in C++17)

adaptor-compatible binary function base class
(class template) [edit] copyable wrapper of any copy constructible callable object
(class template) [edit] move-only wrapper of any callable object that supports qualifiers in a given call signature
(class template) [edit]

(deprecated in C++17)(removed in C++20)

constructs custom std::binary_negate object
(function template) [edit]

(deprecated in C++11)(removed in C++17)

creates an adaptor-compatible function object wrapper from a pointer to function
(function template) [edit]

(deprecated in C++17)(removed in C++20)

wrapper function object returning the complement of the unary predicate it holds
(class template) [edit]

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