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unary_negate


not1

function template
<functional>
template <class Predicate>
  unary_negate<Predicate> not1 (const Predicate& pred);

Return negation of unary function object

This function constructs a function object that has the opposite behavior of pred (its argument, another function object).

Function objects are objects whose class defines member function operator(). This member function allows the object to be used with the same syntax as a regular function call, and therefore it can be used in templates instead of a pointer to a function.

The function object returned by not1 has its operator() defined such that it returns true when pred would return false, and false when pred would return true.

It is defined with the same behavior as:

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template <class Predicate>
  unary_negate<Predicate> not1 (const Predicate& pred)
{
  return unary_negate<Predicate>(pred);
}


not1 is specifically designed to negate function objects (predicates) derived from unary_function (an argument_type member is required). For binary function objects, see not2.

Parameters

Predicate
Unary function object derived from unary_function.

Return value

An unary function object with the opposite behavior of pred.
unary_negate is a type derived from unary_function.

Example

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// not1 example
#include <iostream>
#include <functional>
#include <algorithm>
using namespace std;
struct IsOdd : unary_function<int,bool> {
  bool operator() (const int& x) const {return x%2==1;}
};
int main () {
  int values[] = {1,2,3,4,5};
  int cx;
  cx = count_if ( values, values+5, not1(IsOdd()) );
  cout << "There are " << cx << " elements with even values.\n";
  return 0;
}


Output:

There are 2 elements with even values.

See also

not2 Return negation of binary function object (function template)
unary_negate Generate negation of unary function object class (class template)
unary_function Unary function object base class (class template)