# std::multimap<Key,T,Compare,Allocator>::key_comp

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< cpp‎ | container‎ | multimap

key_compare key_comp() const; |  |

Returns the function object that compares the keys, which is a copy of this container's constructor argument `comp`.

### Parameters

(none)

### Return value

The key comparison function object.

### Complexity

Constant.

### Example

Run this code

    #include <cassert>
    #include <iostream>
    #include <map>

    // 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::multimap<int, char, ModCmp> cont;
        cont = { { 1, 'a' }, { 2, 'b' }, { 3, 'c' }, { 4, 'd' }, { 5, 'e' } };

        auto comp_func = cont.key_comp();

        for (auto it : cont) {
            bool before = comp_func(it.first, 100);
            bool after = comp_func(100, it.first);

            std::cout << '(' << 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
                assert(0); // Cannot happen
        }
    }

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

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

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