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std::multiset::key_comp(3)    C++ Standard Libary   std::multiset::key_comp(3)

NAME
       std::multiset::key_comp - std::multiset::key_comp

Synopsis
	  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.

Example
       // Run this code

	#include <iostream>
	#include <set>
	#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::multiset<int, ModCmp> cont{1, 2, 3, 4,	5};

	    auto comp_func = cont.key_comp();

	    for	(const int key : cont)
	    {
		const bool before = comp_func(key, 100);
		const bool after = comp_func(100, key);

		std::cout << '(' << key	<< ") ";
		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:
	Key (1)	goes before key	(100)
	Key (2)	goes before key	(100)
	Key (3)	equivalent to key (100)
	Key (4)	goes after key (100)
	Key (5)	goes after key (100)

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

http://cppreference.com		  2024.06.10	    std::multiset::key_comp(3)

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