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std::unorde...ap::emplace(3)   C++ Standard Libary  std::unorde...ap::emplace(3)

NAME
     std::unordered_multimap::emplace - std::unordered_multimap::emplace

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

	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.

	If after the operation the new number of elements is greater than old
	max_load_factor() * bucket_count() a rehashing takes place.
	If rehashing occurs (due to the insertion), all  iterators  are  invali-
     dated. Otherwise
	(no rehashing), iterators are not 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
	Amortized constant on average, worst case linear in the size of the con-
     tainer.

Example
     // Run this code

      #include <iostream>
      #include <string>
      #include <utility>
      #include <unordered_map>

      int main()
      {
	  std::unordered_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';
      }

Possible output:
      a => a
      b => abcd
      c => cccccccccc
      d => ddd
      d => DDD

See also
	emplace_hint constructs elements in-place using a hint
		     (public member function)
		     inserts in-place if the key does not exist, does nothing if
     the key
	try_emplace  exists
		     (public member function)
		     inserts elements
	insert	     or nodes
		     (since C++17)
		     (public member function)

http://cppreference.com 	   2024.06.10	    std::unorde...ap::emplace(3)
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