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std::map<Key,T,Compare,Allocator>:: value_comp

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Deduction guides (C++17)
value_compare value_comp ( ) const ;
(C++26부터 constexpr)

value_type 객체들(키-값 쌍)을 비교하는 함수 객체를 반환합니다. 이때 key_comp() 를 사용하여 쌍들의 첫 번째 구성 요소를 비교합니다.

목차

반환값

값 비교 함수 객체.

복잡도

상수.

예제

이 코드 실행 
#include <iostream>
#include <map>
#include <utility>
// Example module 97 key compare function
struct ModCmp
{
    bool operator()(int lhs, int rhs) const
    {
        return (lhs % 97) < (rhs % 97);
    }
};
int main()
{
    std::map<int, char, ModCmp> cont;
    cont = {{1, 'a'}, {2, 'b'}, {3, 'c'}, {4, 'd'}, {5, 'e'}};
    auto comp_func = cont.value_comp();
    for (const std::pair<int, char> val = {100, 'a'}; auto it : cont)
    {
        const bool before = comp_func(it, val);
        const bool after = comp_func(val, it);
        std::cout << '(' << it.first << ',' << it.second << ") ";
        if (!before && !after)
            std::cout << "equivalent to key (" << val.first << ")\n";
        else if (before)
            std::cout << "goes before key (" << val.first << ")\n";
        else if (after)
            std::cout << "goes after key (" << val.first << ")\n";
        else
            std::unreachable();
    }
}

출력: 

(1,a) goes before key (100)
(2,b) goes before key (100)
(3,c) equivalent to key (100)
(4,d) goes after key (100)
(5,e) goes after key (100)

참고 항목

키를 비교하는 함수를 반환합니다
(public member function)