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std::unorde...iset::merge(3)   C++ Standard Libary  std::unorde...iset::merge(3)

NAME
     std::unordered_multiset::merge - std::unordered_multiset::merge

Synopsis
	template<  class  H2, class P2 >				     (1)
     (since C++17)
	void merge( std::unordered_set<Key, H2, P2, Allocator>& source );
	template< class H2, class P2  > 				     (2)
     (since C++17)
	void merge( std::unordered_set<Key, H2, P2, Allocator>&& source );
	template< class H2, class P2 >
	void  merge(  std::unordered_multiset<Key, H2, P2, Allocator>&	     (3)
     (since C++17)
	source );
	template< class H2, class P2 >
	void merge( std::unordered_multiset<Key, H2, P2,  Allocator>&&	     (4)
     (since C++17)
	source );

	Attempts to extract ("splice") each element in source and insert it into
     *this using
	the hash function and key equality predicate 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. Iterators referring to the
     transferred
	elements and all iterators referring to *this are invalidated.

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

Parameters
	source - compatible container to transfer the nodes from

Return value
	(none)

Complexity
	Average  case  O(N),  worst  case  O(N	*  size()  +  N),  where  N   is
     source.size().

Example
     // Run this code

      #include <iostream>
      #include <unordered_set>

      // print out a container
      template<class Os, class K>
      Os& operator<<(Os& os, const std::unordered_multiset<K>& v)
      {
	  os << '[' << v.size() << "] {";
	  bool o{};
	  for (const auto& e : v)
	      os << (o ? ", " : (o = 1, " ")) << e;
	  return os << " }\n";
      }

      int main()
      {
	  std::unordered_multiset<char>
	      p{'C', 'B', 'B', 'A'},
	      q{'E', 'D', 'E', 'C'};

	  std::cout << "p: " << p << "q: " << q;

	  p.merge(q);

	  std::cout << "p.merge(q);\n" << "p: " << p << "q: " << q;
      }

Possible output:
      p: [4] { A, B, B, C }
      q: [4] { C, D, E, E }
      p.merge(q);
      p: [8] { E, E, D, A, B, B, C, C }
      q: [0] { }

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::unorde...iset::merge(3)
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