std::not1 (3) - Linux Man Pages

std::not1: std::not1


std::not1 - std::not1


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.


pred - unary predicate

Return value

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




// 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";



See also

not_fn Creates a function object that returns the complement of the result of the function object it holds
                      (function template)

unary_negate wrapper function object returning the complement of the unary predicate it holds
                      (class template)
(deprecated in C++17)
(removed in C++20)

function wraps callable object of any type with specified function call signature
                      (class template)

not2 constructs custom std::binary_negate object
                      (function template)
(deprecated in C++17)
(removed in C++20)

ptr_fun creates an adaptor-compatible function object wrapper from a pointer to function
                      (function template)
(deprecated in C++11)
(removed in C++17)

unary_function adaptor-compatible unary function base class
                      (class template)
(deprecated in C++11)
(removed in C++17)