std::set key_comp() method

od C++98

// Const version only
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().

Parameters

(none)

Return value

The key comparison function object.

Complexity

Constant - O(1).

Exceptions

(none)

Example

Main.cpp

#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