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std::set<Key,Compare,Allocator>::key_comp

From cppreference.com
< cpp‎ | container‎ | set
 
 
Containers library
Sequence
(C++11)
Associative
Unordered associative
Adaptors
Views
(C++20)
 
 
key_compare key_comp() const;

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

Contents

[edit] Parameters

(none)

[edit] Return value

The key comparison function object.

[edit] Complexity

Constant.

[edit] Example

#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};
 
    auto comp_func = cont.key_comp();
 
    for (int key : cont) {
        bool before = comp_func(key, 100);
        bool after = comp_func(100, key);
        if (!before && !after)
            std::cout << key << " equivalent to key 100\n";
        else if (before)
            std::cout << key << " goes before key 100\n";
        else if (after)
            std::cout << key << " goes after key 100\n";
        else
            assert(0); // Cannot happen
    }
}

Output:

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

[edit] See also

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