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std::multimap::merge(3)        C++ Standard Libary	 std::multimap::merge(3)

NAME
     std::multimap::merge - std::multimap::merge

Synopsis
	template<  class C2 >					      (1) (since
     C++17)
	void merge( std::map<Key, T, C2, Allocator>& source );
	template< class C2 >					     (2)  (since
     C++17)
	void merge( std::map<Key, T, C2, Allocator>&& source );
	template<  class C2 >					      (3) (since
     C++17)
	void merge( std::multimap<Key, T, C2, Allocator>& source );
	template< class C2 >					     (4)  (since
     C++17)
	void merge( std::multimap<Key, T, C2, Allocator>&& source );

	Attempts to extract ("splice") each element in source and insert it into
     *this using
	the comparison object of *this.

	No  elements are copied or moved, only the internal pointers of the con-
     tainer nodes
	are repointed. All pointers and references to the  transferred	elements
     remain valid,
	but now refer into *this, not into source.

	The behavior is undefined if get_allocator() != source.get_allocator().

Parameters
	source - compatible container to transfer the nodes from

Return value
	(none)

Exceptions
	Does not throw unless comparison throws.

Complexity
	N * log(size() + N)), where N is source.size().

Example
     // Run this code

      #include <iostream>
      #include <map>
      #include <string>

      int main()
      {
	  std::multimap<int,  std::string>  ma{{1,  "apple"},  {5, "pear"}, {10,
     "banana"}};
	  std::multimap<int, std::string> mb{{2, "zorro"},  {4,  "batman"},  {5,
     "X"}, {8, "alpaca"}};
	  std::multimap<int, std::string> u;
	  u.merge(ma);
	  std::cout << "ma.size(): " << ma.size() << '\n';
	  u.merge(mb);
	  std::cout << "mb.size(): " << mb.size() << '\n';

	  for (auto const& kv : u)
	      std::cout << kv.first << ", " << kv.second << '\n';
      }

Output:
      ma.size(): 0
      mb.size(): 0
      1, apple
      2, zorro
      4, batman
      5, pear
      5, X
      8, alpaca
      10, banana

See also
	extract extracts nodes from the container
	(C++17) (public member function)
		inserts elements
	insert	or nodes
		(since C++17)
		(public member function)

http://cppreference.com 	   2024.06.10		 std::multimap::merge(3)
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