public member function
<unordered_map>

std::unordered_multimap::swap

void swap ( unordered_multimap& umm );
Swap content
Exchanges the content of the container by the content of umm, which is another unordered_multimap object containing elements of the same type. Sizes may differ.

After the call to this member function, the elements in this container are those which were in umm before the call, and the elements of umm are those which were in this. Other objects kept internally by the containers (such as their hasher or key_equal objects) are also swapped.

This function exchanges internal pointers to data between the containers without actually performing any copies or moves on the individual elements, allowing for constant time execution no matter the sizes.

Notice that a global algorithm function exists with this same name, swap. This global function is overloaded for unordered_multimap arguments to have the same behavior and complexity as this member function.

Parameters

umm
Another unordered_multimap container object of the same type as this.

Return value

none

Example

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// unordered_multimap::swap
#include <iostream>
#include <string>
#include <unordered_map>

int main ()
{
  std::unordered_multimap<std::string,std::string>
     a = {{"orange","FL"},{"apple","NY"},{"apple","WA"}},
     b  = {{"strawberry","LA"},{"strawberry","NC"},{"pear","OR"}};

  a.swap(b);

  std::cout << "a: ";
  for (auto& x: a) std::cout << " " << x.first << ":" << x.second;
  std::cout << std::endl;

  std::cout << "b: ";
  for (auto& x: b) std::cout << " " << x.first << ":" << x.second;
  std::cout << std::endl;

  return 0;
}

Possible output:
a:  pear:OR strawberry:LA strawberry:NC
b:  orange:FL apple:NY apple:WA


Complexity

Constant.

Iterator validity

All iterators, pointers and references remain valid, but now are referring to elements in the other container, and iterate in it.

See also