std::not2(3)

NAME
std::not2 - std::not2

Synopsis
   Defined in header <functional>
   template< class Predicate > (until C++14)
   std::binary_negate<Predicate> not2( const Predicate& pred );
   template< class Predicate > (since C++14)
   constexpr std::binary_negate<Predicate> not2( const (deprecated in C++17)
   Predicate& pred ); (removed in C++20)
   std::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
// Run this code
 #include <algorithm>
 #include <cstddef>
 #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
   not_fn creates a function object that returns the complement of the
   (C++17) result of the function object it holds
                        (function template)
   binary_negate wrapper function object returning the complement of the binary
   (deprecated in C++17) predicate it holds
   (removed in C++20) (class template)
   function wraps callable object of any copy constructible type with
   (C++11) specified function call signature
                        (class template)
   move_only_function wraps callable object of any type with specified function call
   (C++23) signature
                        (class template)
   not1 constructs custom std::unary_negate object
   (deprecated in C++17) (function template)
   (removed in C++20)
   ptr_fun creates an adaptor-compatible function object wrapper from a
   (deprecated in C++11) pointer to function
   (removed in C++17) (function template)
   binary_function adaptor-compatible binary function base class
   (deprecated in C++11) (class template)
   (removed in C++17)