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std::multimap::emplace

From cppreference.com
< cpp‎ | container‎ | multimap
Revision as of 19:19, 2 November 2012 by P12bot (Talk | contribs)

template< class... Args >
iterator emplace( Args&&... args );
(since C++11)

Inserts a new element into the container by constructing it 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.

Contents

Parameters

args - arguments to forward to the constructor of the element

Return value

Returns an iterator to the inserted element.

Exceptions

If an exception is thrown by any operation, this function has no effect.

Complexity

Logarithmic in the size of the container.

Example

#include <iostream>
#include <utility>
#include <string>
 
#include <map>
int main()
{
    std::multimap<std::string, std::string> m;
 
    // uses pair's move constructor (overload 8)
    m.emplace(std::make_pair(std::string("a"), std::string("a")));
 
    // uses pair's converting move constructor (overload 5)
    m.emplace(std::make_pair("b", "abcd"));
 
    // uses pair's template constructor (overload 3)
    m.emplace("d", "ddd");
 
    // uses pair's piecewise constructor (overload 6)
    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

See also

constructs elements in-place using a hint
(public member function) [edit]
inserts elements
(public member function) [edit]