std::set value_comp() 方法

C++98 起

// Const version only
value_compare value_comp() const;

返回比较值的函数对象。它与key_comp()相同。

参数

(无)

返回值

键比较函数对象。

复杂度

常数 - O(1)。

异常

(无)

示例

Main.cpp

#include <cassert>
#include <iostream>
#include <set>
 
// Example module 97 key compare function
struct ModCmp {
    bool operator()(const int lhs, const int rhs) const
    {
        return (lhs % 97) < (rhs % 97);
    }
};
 
int main()
{
    std::set<int, ModCmp> cont{1, 2, 3, 4, 5};
 
    // Same behaviour as key_comp()
    auto comp_func = cont.value_comp();
 
    const int val = 100;
 
    for (int key : cont) {
        bool before = comp_func(key, val);
        bool after = comp_func(val, key);
        if (!before && !after)
            std::cout << key << " equivalent to key " << val << '\n';
        else if (before)
            std::cout << key << " goes before key " << val << '\n';
        else if (after)
            std::cout << key << " goes after key " << val << '\n';
        else
            assert(0); // Cannot happen
    }
}

输出

1 goes before key 100
2 goes before key 100
3 equivalent to key 100
4 goes after key 100
5 goes after key 100