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

template< class... Args >
iterator emplace( Args&&... args );

(since C++11)

Inserts a new element into the container constructed in-place with the given args.

The constructor of the new element (i.e. std::pair<const Key, T>) is called with exactly the same arguments as supplied to emplace, forwarded via std::forward<Args>(args)....

Careful use of emplace allows the new element to be constructed while avoiding unnecessary copy or move operations.

No iterators or references are invalidated.

Parameters

args

arguments to forward to the constructor of the element

Return value

An iterator to the inserted element.

Exceptions

If an exception is thrown for any reason, this function has no effect (strong exception safety guarantee).

Complexity

Logarithmic in the size of the container.

Example

#include <iostream>
#include <string>
#include <utility>
#include <map>

int main()
{
    std::multimap<std::string, std::string> m;

    // uses pair's move constructor
    m.emplace(std::make_pair(std::string("a"), std::string("a")));

    // uses pair's converting move constructor
    m.emplace(std::make_pair("b", "abcd"));

    // uses pair's template constructor
    m.emplace("d", "ddd");

    // emplace with duplicate key 
    m.emplace("d", "DDD");

    // uses pair's piecewise constructor
    m.emplace(std::piecewise_construct,
              std::forward_as_tuple("c"),
              std::forward_as_tuple(10, 'c'));

    for (const auto& p : m)
        std::cout << p.first << " => " << p.second << '\n';
}

Output:

a => a
b => abcd
c => cccccccccc
d => ddd
d => DDD