std::unordered_multimap::emplace

From cppreference.com


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

Inserts a new element to the container. The element is constructed in-place, i.e. no copy or move operations are performed. The constructor of the element type (value_type, that is, std::pair<const Key, T>) is called with exactly the same arguments as supplied to the function, forwarded with std::forward<Args>(args)....

If rehashing occurs due to the insertion, all iterators are invalidated. Otherwise iterators are not affected. References are not invalidated. Rehashing occurs only if the new number of elements is higher than max_load_factor()*bucket_count().

#include <iostream>
#include <utility>
#include <unordered_map>
 
int main()
{
    std::unordered_multimap<std::string, std::string> m;
 
    // uses pair's copy-constructor
    m.emplace(std::make_pair(std::string("a"), std::string("a")));
 
    // uses pair's converting copy 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';
    }
}

Possible output:

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

[edit] See also


emplace_hint	constructs elements in-place using a hint (public member function)

insert	inserts elements (public member function)

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)

std::unordered_multimap::emplace

Contents

[edit] Parameters

[edit] Return value

[edit] Complexity

[edit] Example

[edit] See also