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對象的 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.