std::binary_negate

C++

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Defined in header <functional>
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)

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.

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

Member types

Type	Definition
first_argument_type	Predicate::first_argument_type
second_argument_type	Predicate::second_argument_type
result_type	bool

Member functions

(constructor)	constructs a new binary_negate object with the supplied predicate (public member function)
operator()	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)
explicit constexpr binary_negate( Predicate const& pred );		(since C++14)

Constructs a 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).

Example

Run this code

#include <algorithm>
#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;
    std::vector<int> v2;
    for (int i = 0; i < 10; ++i) v1.push_back(i);
    for (int i = 0; i < 10; ++i) v2.push_back(10 - i);

    std::vector<bool> v3(v1.size());

    std::binary_negate<same> not_same((same()));

    std::transform(v1.begin(), v1.end(), v2.begin(), v3.begin(), not_same);

    /* C++11 solution:
        // Use std::function<bool (int, int)>
        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 (int i = 0; i < 10; ++i)
        std::cout << v1[i] << ' ' << v2[i] << ' ' << v3[i] << '\n';
}

Output:

0 10 true
1 9 true
2 8 true
3 7 true
4 6 true
5 5 false
6 4 true
7 3 true
8 2 true
9 1 true

See also

binary_function (deprecated in C++11)(removed in C++17)	adaptor-compatible binary function base class (class template)
function (C++11)	wraps callable object of any type with specified function call signature (class template)
not2 (deprecated in C++17)(removed in C++20)	constructs custom std::binary_negate object (function template)
ptr_fun (deprecated in C++11)(removed in C++17)	creates an adaptor-compatible function object wrapper from a pointer to function (function template)
unary_negate (deprecated in C++17)(removed in C++20)	wrapper function object returning the complement of the unary predicate it holds (class template)