std::not2

Defined in header <functional> 
template< class Predicate >
std::binary_negate<Predicate> not2(const Predicate& pred);
 (until C++14) 
template< class Predicate >
constexpr std::binary_negate<Predicate> not2(const Predicate& pred);
 (since C++14)
(deprecated in C++17)
(removed in C++20)

not2 is a helper function to create a function object that returns the complement of the binary predicate function passed. The function object created is of type std::binary_negate<Predicate>.

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 another call to std::not2 have these types defined, as are function objects derived from the deprecated std::binary_function.

Parameters

pred - binary predicate

Return value

std::not2 returns an object of type std::binary_negate<Predicate>, constructed with pred.

Exceptions

None.

Example

#include <algorithm>
#include <functional>
#include <iostream>
#include <vector>
 
struct old_same : std::binary_function<int, int, bool>
{
    bool operator()(int a, int b) const { return a == b; }
};
 
struct new_same
{
    bool operator()(int a, int b) const { return a == b; }
};
 
bool same_fn(int a, int b)
{
    return a == b;
}
 
 
int main()
{
    std::vector<int> v1{0, 1, 2};
    std::vector<int> v2{2, 1, 0};
    std::vector<bool> v3(v1.size());
 
    std::cout << "negating a binary_function:\n";
    std::transform(v1.begin(), v1.end(), v2.begin(), v3.begin(),
                   std::not2(old_same()));
 
    std::cout << std::boolalpha;
    for (std::size_t i = 0; i < v1.size(); ++i)
        std::cout << v1[i] << ' ' << v2[i] << ' ' << v3[i] << '\n';
 
    std::cout << "negating a standard functor:\n";
    std::transform(v1.begin(), v1.end(), v2.begin(), v3.begin(),
                   std::not2(std::equal_to<int>()));
 
    for (std::size_t i = 0; i < v1.size(); ++i)
        std::cout << v1[i] << ' ' << v2[i] << ' ' << v3[i] << '\n';
 
    std::cout << "negating a std::function:\n";
    std::transform(v1.begin(), v1.end(), v2.begin(), v3.begin(),
                   std::not2(std::function<bool(int,int)>(new_same())));
 
    for (std::size_t i = 0; i < v1.size(); ++i)
        std::cout << v1[i] << ' ' << v2[i] << ' ' << v3[i] << '\n';
 
    std::cout << "negating a std::reference_wrapper:\n";
    std::transform(v1.begin(), v1.end(), v2.begin(), v3.begin(),
                   std::not2(std::ref(same_fn)));
 
    for (std::size_t i = 0; i < v1.size(); ++i)
        std::cout << v1[i] << ' ' << v2[i] << ' ' << v3[i] << '\n';
 
}

Output:

negating a binary_function:
0 2 true
1 1 false
2 0 true
negating a standard functor:
0 2 true
1 1 false
2 0 true
negating a std::function:
0 2 true
1 1 false
2 0 true
negating a std::reference_wrapper:
0 2 true
1 1 false
2 0 true

See also

(C++17)
 Creates a function object that returns the complement of the result of the function object it holds
(function template)
(deprecated in C++17)(removed in C++20)
 wrapper function object returning the complement of the binary predicate it holds
(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::unary_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++11)(removed in C++17)
 adaptor-compatible binary function base class
(class template)

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