unary_negate


class template
<functional>
template <class Predicate> class unary_negate;

Generate negation of unary function object class

Generates a function object class that negates the behavior of an unary function object class.

unary_negate is generally used as a type. The function not1 (also defined in header <functional>) can be used to directly construct an object of this type.

unary_negate is constructed using an unary function object as argument. A copy of this object is used by its member operator() to return true whenever the original object would return false, and false whenever the object would return true, inverting its behavior.

This class is derived from unary_function and is defined as:

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template <class Predicate> class unary_negate
  : public unary_function <typename Predicate::argument_type,bool>
{
protected:
  Predicate fn;
public:
  explicit unary_negate ( const Predicate& pred ) : fn (pred) {}
  bool operator() (const typename Predicate::argument_type& x) const
  { return !fn(x); }
};


unary_negate class is specifically designed to negate function objects (predicates) derived from unary_function (it requires an argument_type member).

Members

constructor
Constructs an object with the opposite behavior than the object passed as its argument.
operator()
Member function returning the opposite of the function object with which the object was constructed.


Example

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// unary_negate example
#include <iostream>
#include <functional>
#include <algorithm>
using namespace std;

struct IsOdd_class : unary_function<int,bool> {
  bool operator() (const int& x) const {return x%2==1;}
} IsOdd_object;

int main () {
  unary_negate<IsOdd_class> IsEven_object (IsOdd_object);
  int values[] = {1,2,3,4,5};
  int cx;
  cx = count_if ( values, values+5, IsEven_object );
  cout << "There are " << cx << " elements with even values.\n";
  return 0;
}


Output:

There are 2 elements with even values.


See also

not1 Return negation of unary function object (function template)
binary_negate Generate negation of binary function object class (class template)
unary_function Unary function object base class (class template)