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std::unorde...ltimap::swap(3) C++ Standard Libarystd::unorde...ltimap::swap(3)

NAME
       std::unordered_multimap::swap - std::unordered_multimap::swap

Synopsis
	  void	       swap(	    unordered_multimap&	       other	    );
       (since C++11)
									     (un-
       til C++17)
	  void swap( unordered_multimap& other ) noexcept(/*  see  below  */);
       (since C++17)

	  Exchanges  the  contents  of the container with those	of other. Does
       not invoke any
	  move,	copy, or swap operations on individual elements.

	  All iterators	and references remain valid. The past-the-end iterator
       is invalidated.

	  The Hash and KeyEqual	objects	must be	Swappable, and	they  are  ex-
       changed using
	  unqualified calls to non-member swap.

	  If	      std::allocator_traits<allocator_type>::propagate_on_con-
       tainer_swap::value
	  is true, then	the allocators are exchanged using an unqualified call
       to	(since
	  non-member swap. Otherwise, they are not swapped (and	if get_alloca-
       tor() !=	  C++11)
	  other.get_allocator(), the behavior is undefined).

Parameters
	  other	- container to exchange	the contents with

Return value
	  (none)

Exceptions
	  Any exception	thrown by the swap of the Hash	or  KeyEqual  objects.
       (until C++17)
	  noexcept specification:
	  noexcept(std::allocator_traits<Allocator>::is_always_equal::value
									    (since
       C++17)
	  && std::is_nothrow_swappable<Hash>::value

	  && std::is_nothrow_swappable<key_equal>::value)

Complexity
	  Constant.

Example
       // Run this code

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

	// print out a std::pair
	template <class	Os, class U, class V>
	Os& operator<<(Os& os, const std::pair<U, V>& p) {
	    return os << p.first << ":"	<< p.second;
	}

	// print out a container
	template <class	Os, class Co>
	Os& operator<<(Os& os, const Co& co) {
	    os << "{";
	    for	(auto const& i : co) { os << ' ' << i; }
	    return os << " }\n";
	}

	int main()
	{
	    std::unordered_multimap<std::string, std::string>
		m1   {	{"",  "gamma"},	 {"",  "beta"},	 {"",  "alpha"},  {"",
       "gamma"}, },
		m2 { {"", "epsilon"}, {"", "delta"}, {"", "epsilon"} };

	    const auto&	ref = *(m1.begin());
	    const auto iter = std::next(m1.cbegin());

	    std::cout << " before swap \n"
		      << "m1: "	<< m1 << "m2: "	<< m2 << "ref: " << ref
		      << "\niter: " << *iter <<	'\n';

	    m1.swap(m2);

	    std::cout << " after swap \n"
		      << "m1: "	<< m1 << "m2: "	<< m2 << "ref: " << ref
		      << "\niter: " << *iter <<	'\n';

	    // Note that every iterator	referring to an	element	 in  one  con-
       tainer before
	    //	the swap refers	to the same element in the other container af-
       ter the swap.
	    // Same is true for	references.
	}

Possible output:
	 before	swap
	m1: { :alpha :beta :gamma :gamma }
	m2: { :delta :epsilon :epsilon }
	ref: :alpha
	iter: :beta
	 after swap
	m1: { :delta :epsilon :epsilon }
	m2: { :alpha :beta :gamma :gamma }
	ref: :alpha
	iter: :beta

See also
	  std::swap(std::unordered_multimap) specializes the  std::swap	 algo-
       rithm
	  (C++11)			     (function template)

http://cppreference.com		  2022.07.31	 std::unorde...ltimap::swap(3)

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