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

 

C++

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Symbols index

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array (C++11)

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unordered_set (C++11)

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stack

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flat_multimap (C++23)

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std::multimap

Member functions

multimap::multimap multimap::~multimap        multimap::operator= multimap::get_allocator

Iterators multimap::beginmultimap::cbegin (C++11) multimap::endmultimap::cend (C++11) multimap::rbeginmultimap::crbegin (C++11)    multimap::rendmultimap::crend (C++11) Capacity multimap::size multimap::max_size multimap::empty Observers multimap::key_comp multimap::value_comp Modifiers multimap::clear multimap::insert multimap::erase multimap::swap multimap::merge (C++17) multimap::insert_range (C++23) multimap::emplace (C++11) multimap::emplace_hint (C++11) multimap::extract (C++17) Lookup multimap::count multimap::find multimap::contains (C++20) multimap::equal_range multimap::lower_bound multimap::upper_bound

Non-member functions

operator==operator<=> (C++20) std::swap(std::multimap) erase_if(std::multimap) (C++20)   operator!=operator<operator>operator<=operator>= (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)

Deduction guides(C++17)

 

std::multimap::value_compare value_comp() const;

Returns a function object that compares objects of type std::multimap::value_type (key-value pairs) by using key_comp to compare the first components of the pairs.

Parameters

(none)

Return value

The value comparison function object.

Complexity

Constant.

Example

Run this code

#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.value_comp();
 
    for (const std::pair<int, char> val = {100, 'a'}; auto it : cont)
    {
        const bool before = comp_func(it, val);
        const bool after = comp_func(val, it);
 
        std::cout << '(' << it.first << ',' << it.second << ") ";
        if (!before && !after)
            std::cout << "equivalent to key (" << val.first << ")\n";
        else if (before)
            std::cout << "goes before key (" << val.first << ")\n";
        else if (after)
            std::cout << "goes after key (" << val.first << ")\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)

See also

key_comp

returns the function that compares keys (public member function)