C++ multimap - swap() Function

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

Syntax

C++98
C++11

template<class Key, class T, class Compare, class Alloc>
void swap(
    multimap<Key,T,Compare,Alloc>& lhs,
    multimap<Key,T,Compare,Alloc>& rhs 
);

template<class Key, class T, class Compare, class Alloc>
void swap(
    multimap<Key,T,Compare,Alloc>& lhs,
    multimap<Key,T,Compare,Alloc>& rhs 
);

Parameters

`lhs`	First multimap.
`rhs`	Second multimap.

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 multimap MyMMap1 with all elements of multimap MyMMap2.

#include <iostream>
#include <map>
using namespace std;
 
int main (){
  multimap<string, string> MyMMap1;
  multimap<string, string> MyMMap2;
  multimap<string, string>::iterator it;

  //elements of MyMMap1
  MyMMap1.insert(pair<string, string>("USA", "New York"));
  MyMMap1.insert(pair<string, string>("USA", "Washington"));  
  MyMMap1.insert(pair<string, string>("CAN", "Toronto"));

  //elements of MyMMap2
  MyMMap2.insert(pair<string, string>("CAN", "Montreal"));
  MyMMap2.insert(pair<string, string>("IND", "Delhi"));

  cout<<"Before Swapping, The MyMMap1 contains:\n";
  for(it = MyMMap1.begin(); it != MyMMap1.end(); ++it)
    cout<<it->first<<"  "<<it->second<<"\n";
  cout<<"\nBefore Swapping, The MyMMap2 contains:\n";
  for(it = MyMMap2.begin(); it != MyMMap2.end(); ++it)
    cout<<it->first<<"  "<<it->second<<"\n";

  swap(MyMMap1, MyMMap2);

  cout<<"\n\nAfter Swapping, The MyMMap1 contains:\n";
  for(it = MyMMap1.begin(); it != MyMMap1.end(); ++it)
    cout<<it->first<<"  "<<it->second<<"\n";
  cout<<"\nAfter Swapping, The MyMMap2 contains:\n";
  for(it = MyMMap2.begin(); it != MyMMap2.end(); ++it)
    cout<<it->first<<"  "<<it->second<<"\n";

  return 0;
}

The output of the above code will be:

Before Swapping, The MyMMap1 contains:
CAN  Toronto
USA  New York
USA  Washington

Before Swapping, The MyMMap2 contains:
CAN  Montreal
IND  Delhi


After Swapping, The MyMMap1 contains:
CAN  Montreal
IND  Delhi

After Swapping, The MyMMap2 contains:
CAN  Toronto
USA  New York
USA  Washington

❮ C++ <map> Library