home | help 
std::unordered_set::merge(3)   C++ Standard Libary  std::unordered_set::merge(3)

NAME
     std::unordered_set::merge - std::unordered_set::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. If there is an
     element in
	*this with key equivalent to the key of an  element  from  source,  then
     that element is
	not extracted from source. No elements are copied or moved, only the in-
     ternal
	pointers  of  the container nodes are repointed. All pointers and refer-
     ences to the
	transferred elements remain valid, but now refer into  *this,  not  into
     source.
	Iterators referring to the transferred elements and all iterators refer-
     ring to *this
	are invalidated. Iterators to elements remaining in source remain valid.

	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_set<K>& v)
      {
	  os << '[' << v.size() << "] {";
	  bool o{};
	  for (const auto& e : v)
	      os << (o ? ", " : (o = 1, " ")) << e;
	  return os << " }\n";
      }

      int main()
      {
	  std::unordered_set<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: [3] { A, B, C }
      q: [3] { C, D, E }
      p.merge(q);
      p: [5] { E, D, A, B, C }
      q: [1] { C }

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::unordered_set::merge(3)
home | help