std::binary_negate

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

#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

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

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