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std::multiset::emplace(3)      C++ Standard Libary     std::multiset::emplace(3)

NAME
     std::multiset::emplace - std::multiset::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 is called with exactly the same argu-
     ments 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.

	No iterators or references are 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
	Logarithmic in the size of the container.

Example
     // Run this code

      #include <chrono>
      #include <cstddef>
      #include <functional>
      #include <iomanip>
      #include <iostream>
      #include <string>
      #include <set>

      class Dew
      {
      private:
	  int a, b, c;

      public:
	  Dew(int _a, int _b, int _c)
	      : a(_a), b(_b), c(_c)
	  {}

	  bool operator<(const Dew& other) const
	  {
	      return (a < other.a) ||
		     (a == other.a && b < other.b) ||
		     (a == other.a && b == other.b && c < other.c);
	  }
      };

      constexpr int nof_operations{101};

      std::size_t set_emplace()
      {
	  std::multiset<Dew> set;
	  for (int i = 0; i < nof_operations; ++i)
	      for (int j = 0; j < nof_operations; ++j)
		  for (int k = 0; k < nof_operations; ++k)
		      set.emplace(i, j, k);

	  return set.size();
      }

      std::size_t set_insert()
      {
	  std::multiset<Dew> set;
	  for (int i = 0; i < nof_operations; ++i)
	      for (int j = 0; j < nof_operations; ++j)
		  for (int k = 0; k < nof_operations; ++k)
		      set.insert(Dew(i, j, k));

	  return set.size();
      }

      void time_it(std::function<int()> set_test, std::string what = "")
      {
	  const auto start = std::chrono::system_clock::now();
	  const auto the_size = set_test();
	  const auto stop = std::chrono::system_clock::now();
	  const std::chrono::duration<double, std::milli> time = stop - start;
	  if (!what.empty() && the_size)
	      std::cout << std::fixed << std::setprecision(2)
			<< time << " for " << what << '\n';
      }

      int main()
      {
	  time_it(set_insert, "cache warming...");
	  time_it(set_insert, "insert");
	  time_it(set_insert, "insert");
	  time_it(set_emplace, "emplace");
	  time_it(set_emplace, "emplace");
      }

Possible output:
      499.61ms for cache warming...
      447.89ms for insert
      436.77ms for insert
      430.62ms for emplace
      428.61ms for emplace

See also
	emplace_hint constructs elements in-place using a hint
	(C++11)      (public member function)
		     inserts elements
	insert	     or nodes
		     (since C++17)
		     (public member function)

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