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std::flat_map<Key,T,Compare,KeyContainer,MappedContainer>:: key_comp

From cppreference.net

C++
Containers library
std::flat_map
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key_compare key_comp ( ) const ;
(since C++23)
(constexpr since C++26)

Returns the function object that compares the keys, which is a copy of the key comparison object used by * this .

Contents

Return value

The key comparison function object.

Complexity

Constant.

Example

Run this code 
#include <iostream>
#include <flat_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::flat_map<int, char, ModCmp> cont;
    cont = {{1, 'a'}, {2, 'b'}, {3, 'c'}, {4, 'd'}, {5, 'e'}};
    auto comp_func = cont.key_comp();
    for (const auto it : cont)
    {
        const bool before = comp_func(it.first, 100);
        const bool after = comp_func(100, it.first);
        std::cout << "Key (" << it.first << ',' << it.second << ") ";
        if (!before && !after)
            std::cout << "equivalent to key (100)\n";
        else if (before)
            std::cout << "goes before key (100)\n";
        else if (after)
            std::cout << "goes after key (100)\n";
        else
            std::unreachable();
    }
}

Output: 

(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)

See also

returns the function that compares keys in objects of type value_type
(public member function)