std::not1 (3) - Linux Manuals

std::not1: std::not1

NAME

std::not1 - std::not1

Synopsis

Defined in header <functional>
template< class Predicate > (until C++14)
std::unary_negate<Predicate> not1(const Predicate& pred);
template< class Predicate > (since C++14)
constexpr std::unary_negate<Predicate> not1(const Predicate& pred); (deprecated in C++17)
                                                                     (removed in C++20)

not1 is a helper function to create a function object that returns the complement of the unary predicate function passed. The function object created is of type std::unary_negate<Predicate>.
The unary predicate type must define a member type, argument_type, that is convertible to the predicate's parameter type. The unary function objects obtained from std::ref, std::cref, std::negate, std::logical_not, std::mem_fn, std::function, std::hash, or from another call to std::not1 have this type defined, as are function objects derived from the deprecated std::unary_function.

Parameters

pred - unary predicate

Return value

std::not1 returns an object of type std::unary_negate<Predicate>, constructed with pred.

Exceptions

None.

Example

// Run this code

  #include <algorithm>
  #include <numeric>
  #include <iterator>
  #include <functional>
  #include <iostream>
  #include <vector>

  struct LessThan7 : std::unary_function<int, bool>
  {
      bool operator()(int i) const { return i < 7; }
  };

  int main()
  {
      std::vector<int> v(10);
      std::iota(begin(v), end(v), 0);

      std::cout << std::count_if(begin(v), end(v), std::not1(LessThan7())) << "\n";

      //same as above, but using `std::function`
      std::function<bool(int)> less_than_9 = [](int x){ return x < 9; };
      std::cout << std::count_if(begin(v), end(v), std::not1(less_than_9)) << "\n";
  }

Output:

  3
  1