public member function
<map>

std::multimap::emplace

template <class... Args>
  iterator emplace (Args&&... args);
Construct and insert element
Inserts a new element in the multimap. This new element is constructed in place using args as the arguments for the construction of a value_type (which is an object of a pair type).

This effectively increases the container size by one.

Internally, multimap containers keep all their elements sorted by key following the criterion specified by its comparison object. The element is always inserted in its respective position following this ordering.

The element is constructed in-place by calling allocator_traits::construct with args forwarded.

A similar member function exists, insert, which either copies or moves existing objects into the container.

The relative ordering of elements with equivalent keys is preserved, and newly inserted elements follow those with equivalent keys already in the container.

Parameters

args
Arguments used to construct a new object of the mapped type for the inserted element.
Arguments forwarded to construct the new element (of type pair<const key_type, mapped_type>).
This can be one of:
- Two arguments: one for the key, the other for the mapped value.
- A single argument of a pair type with a value for the key as first member, and a value for the mapped value as second.
- piecewise_construct as first argument, and two additional arguments with tuples to be forwarded as arguments for the key value and for the mapped value respectivelly.
See pair::pair for more info.

Return value

An iterator to the newly inserted element.

Member type iterator is a bidirectional iterator type that points to an element.

Example

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// multimap::emplace
#include <iostream>
#include <string>
#include <map>

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

  mymultimap.emplace("apple",1.50);
  mymultimap.emplace("coffee",2.10);
  mymultimap.emplace("apple",1.40);

  std::cout << "mymultimap contains:";
  for (auto& x: mymultimap)
    std::cout << " [" << x.first << ':' << x.second << ']';
  std::cout << '\n';

  return 0;
}

Output:
mymultimap contains: [apple:1.5] [apple:1.4] [coffee:2.1]

Complexity

Logarithmic in the container size.

Iterator validity

No changes.

Data races

The container is modified.
Concurrently accessing existing elements is safe, although iterating ranges in the container is not.

Exception safety

Strong guarantee: if an exception is thrown, there are no changes in the container.
If allocator_traits::construct is not supported with the appropriate arguments, it causes undefined behavior.

See also

  • 997351548 2018-02-20
  • 903691547 2018-02-20
  • 9127171546 2018-02-20
  • 2234751545 2018-02-20
  • 1685381544 2018-02-20
  • 911091543 2018-02-20
  • 9281021542 2018-02-20
  • 632231541 2018-02-20
  • 9751491540 2018-02-20
  • 8333621539 2018-02-20
  • 995001538 2018-02-20
  • 6477441537 2018-02-20
  • 511981536 2018-02-19
  • 2072881535 2018-02-19
  • 6024461534 2018-02-19
  • 7594061533 2018-02-19
  • 9311341532 2018-02-19
  • 4928331531 2018-02-19
  • 38561530 2018-02-19
  • 7776611529 2018-02-19