unary_negate 類別

提供成員函式的類別範本，會否定指定一元函式的傳回值。 在 C++17 中已被取代， 有利於not_fn 。

語法

template <class Predicate>
class unary_negate
    : public unaryFunction<typename Predicate::argument_type, bool>
{
    explicit unary_negate(const Predicate& Func);
    bool operator()(const typename Predicate::argument_type& left) const;
};

參數

Func
要變為負值的一元函式。

left
要變為負值之一元函式的運算元。

傳回值

一元函式的負運算。

備註

類別範本會儲存一元函式物件的 複本_Func 。 它會將其成員函 operator() 式定義為傳 !_Func(left) 回 。

unary_negate 的建構函式很少會直接使用。 Helper 函式 not1 提供宣告和使用 unary_negator 配接器述詞的更簡易方式。

範例

// 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;
}

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.