std::binary_negate

 

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unary_function (until C++17*) binary_function (until C++17*) ptr_fun (until C++17*) pointer_to_unary_function (until C++17*) pointer_to_binary_function (until C++17*)   mem_fun (until C++17*) mem_fun_tmem_fun1_tconst_mem_fun_tconst_mem_fun1_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) not1 (until C++20*) not2 (until C++20*)	binder1stbinder2nd (until C++17*)(until C++17*) bind1stbind2nd (until C++17*)(until C++17*) mem_fun_ref (until C++17*) mem_fun_ref_tmem_fun1_ref_tconst_mem_fun_ref_tconst_mem_fun1_ref_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) unary_negate (until C++20*) binary_negate (until C++20*)

 

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)

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.

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)
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).

Example

Run this code

#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

See also

binary_function (deprecated in C++11)(removed in C++17)	adaptor-compatible binary function base class (class template)
function (C++11)	copyable wrapper of any copy constructible callable object (class template)
move_only_function (C++23)	move-only wrapper of any callable object that supports qualifiers in a given 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)