C++ unordered_set - swap() Function

The C++ unordered_set swap() function is used to exchange all elements of one unordered_set with all elements of another unordered_set. To apply this function, the data-type of both unordered_sets must be same, although the size may differ.

Syntax

C++11

template<class Key, class Hash, class Pred, class Alloc>
void swap(
    unordered_set<Key,Hash,Pred,Alloc>& lhs,
    unordered_set<Key,Hash,Pred,Alloc>& rhs 
);

Parameters

`lhs`	First unordered_set.
`rhs`	Second unordered_set.

Return Value

None.

Time Complexity

Constant i.e, Θ(1)

Example:

In the example below, the swap() function is used to exchange all elements of unordered_set uSet1 with all elements of unordered_set uSet2.

#include <iostream>
#include <unordered_set>
using namespace std;
 
int main (){
  unordered_set<int> uSet1{10, 20, 30, 40, 50};
  unordered_set<int> uSet2{5, 55, 555};

  unordered_set<int>::iterator it;

  cout<<"Before Swapping, The uSet1 contains:";
  for(it = uSet1.begin(); it != uSet1.end(); ++it)
    cout<<" "<<*it;
  cout<<"\nBefore Swapping, The uSet2 contains:";
  for(it = uSet2.begin(); it != uSet2.end(); ++it)
    cout<<" "<<*it;

  swap(uSet1, uSet2);

  cout<<"\n\nAfter Swapping, The uSet1 contains:";
  for(it = uSet1.begin(); it != uSet1.end(); ++it)
    cout<<" "<<*it;
  cout<<"\nAfter Swapping, The uSet2 contains:";
  for(it = uSet2.begin(); it != uSet2.end(); ++it)
    cout<<" "<<*it;

  return 0;
}

The output of the above code will be:

Before Swapping, The uSet1 contains: 50 40 30 20 10
Before Swapping, The uSet2 contains: 555 55 5

After Swapping, The uSet1 contains: 555 55 5
After Swapping, The uSet2 contains: 50 40 30 20 10

❮ C++ <unordered_set> Library