std::not2 (3) - Linux Manuals

std::not2: std::not2

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 Predicate& pred); (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

// Run this code

  #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