unary_negate Class

Article
01/02/2018

The latest version of this topic can be found at unary_negate Class.

A template class providing a member function that negates the return value of a specified unary function.

Syntax

template <class Predicate>  
class unary_negate       : public unary_function<typename Predicate::argument_type, bool>     {    public:    explicit unary_negate(const Predicate& _Func);

    bool operator()(const typename Predicate::argument_type& left) const;

 };

Parameters

_Func
The unary function to be negated.

left
The operand of the unary function to be negated.

Return Value

The negation of the unary function.

Remarks

The template class stores a copy of a unary function object _ Func. It defines its member function operator() as returning !_ Func(left).

The constructor of unary_negate is rarely used directly. The helper function not1 provides an easier way to declare and use the unary_negator adaptor predicate.

Example

// functional_unary_negate.cpp  
// compile with: /EHsc  
#include <vector>  
#include <functional>  
#include <algorithm>  
#include <iostream>  
  
using namespace std;  
  
int main()  
{  
    vector<int> v1;  
    vector<int>::iterator Iter;  
  
    int i;  
    for (i = 0; i <= 7; i++)  
    {  
        v1.push_back(5 * i);  
    }  
  
    cout << "The vector v1 = ( ";  
    for (Iter = v1.begin(); Iter != v1.end(); Iter++)  
        cout << *Iter << " ";  
    cout << ")" << endl;  
  
    vector<int>::iterator::difference_type result1;  
    // Count the elements greater than 10  
    result1 = count_if(v1.begin(), v1.end(), bind2nd(greater<int>(), 10));  
    cout << "The number of elements in v1 greater than 10 is: "  
         << result1 << "." << endl;  
  
    vector<int>::iterator::difference_type result2;  
    // Use the negator to count the elements less than or equal to 10  
    result2 = count_if(v1.begin(), v1.end(),  
        unary_negate<binder2nd <greater<int> > >(bind2nd(greater<int>(),10)));  
  
    // The following helper function not1 also works for the above line  
    // not1(bind2nd(greater<int>(), 10)));  
  
    cout << "The number of elements in v1 not greater than 10 is: "  
         << result2 << "." << endl;  
}  
/* Output:  
The vector v1 = ( 0 5 10 15 20 25 30 35 )  
The number of elements in v1 greater than 10 is: 5.  
The number of elements in v1 not greater than 10 is: 3.  
*/

Requirements

Header: <functional>

Namespace: std