std::multimap emplace() method

od C++11

// Non const version only
template< class... Args >
iterator emplace( Args&&... args );

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

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

No iterators or references are invalidated.

Parameters

• args - arguments to forward to the constructor of the element

Return value

Returns an iterator to the inserted element.

Complexity

Logarithmic in the size of the container - O(log size()).

Exceptions

If an exception is thrown by any operation, this function has no effect (strong exception guarantee).

Example

Main.cpp

#include <iostream>
#include <utility>
#include <string>
#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");
 
    // 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