std::unary_negate (3) - Linux Manuals

std::unary_negate: std::unary_negate

NAME

std::unary_negate - std::unary_negate

Synopsis

Defined in header <functional>
template< class Predicate > (until C++11)
struct unary_negate : public std::unary_function<Predicate::argument_type, bool>;
template< class Predicate > (since C++11)
struct unary_negate; (deprecated in C++17)
                                                                                   (removed in C++20)

unary_negate is a wrapper function object returning the complement of the unary predicate it holds.
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.
unary_negate objects are easily constructed with helper function std::not1.

Member types

Type Definition
argument_type Predicate::argument_type
result_type bool

Member functions

              constructs a new unary_negate object with the supplied predicate
constructor (public member function)
              returns the logical complement of the result of a call to the stored predicate
operator() (public member function)

 std::unary_negate::unary_negate

explicit unary_negate( Predicate const& pred ); (until C++14)
explicit constexpr unary_negate( Predicate const& pred ); (since C++14)

Constructs a unary_negate function object with the stored predicate pred.

Parameters

pred - predicate function object

 std::unary_negate::operator()

bool operator()( argument_type const& x ) const; (until C++14)
constexpr bool operator()( argument_type const& x ) const; (since C++14)

Returns the logical complement of the result of calling pred(x).

Parameters

x - argument to pass through to predicate

Return value

The logical complement of the result of calling pred(x).

Example

// Run this code

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

  struct less_than_7 : std::unary_function<int, bool>
  {
      bool operator()(int i) const { return i < 7; }
  };

  int main()
  {
      std::vector<int> v;
      for (int i = 0; i < 10; ++i) v.push_back(i);

      std::unary_negate<less_than_7> not_less_than_7((less_than_7()));

      std::cout << std::count_if(v.begin(), v.end(), not_less_than_7);

      /* C++11 solution:
          // Use std::function<bool (int)>
          std::function<bool (int)> not_less_than_7 =
              [](int x)->bool{ return !less_than_7()(x); };

          std::cout << std::count_if(v.begin(), v.end(), not_less_than_7);
      */
  }

Output:

  3