Namespaces
Variants
Views
Actions

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

From cppreference.com
< 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.

Contents

[edit] Parameters

(none)

[edit] Return value

The key comparison function object.

[edit] Complexity

Constant.

[edit] Example

#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::multimap<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)

[edit] See also

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