The std::unordered_map::swap() is a built in function in C++ STL which swaps the elements of a container to an other container. After the call of this function elements of the caller unordered_map will be elements of called unordered_map while elements of called unordered_map will be elements of caller unordered_map.
Internally swapping of elements is not done only reference type of both unordered_map is changed.
Syntax
unordered_map.swap ( unordered_map& ump )
Return type : Return type of this function is void.
Parameters : An other unordered_map with same type of elements.
Complexity : Its complexity is constant.
Example 1
// C++ code to illustrate the method // unordered_map swap #include <bits/stdc++.h> using namespace std;
int main()
{ unordered_map< int , int > sample1, sample2;
// Map initialization
sample1 = { { 2, 2 }, { 3, 4 }, { 4, 6 }, { 5, 8 } };
sample2 = { { 10, 11 }, { 12, 13 }, { 14, 15 }, { 26, 17 } };
// printing details before calling swap
cout << " Elements of maps before swap \n" ;
cout << " Elements of first map are : \n" ;
for ( auto & x : sample1)
cout << x.first << " : " << x.second << endl;
cout << " Elements of second map are : \n" ;
for ( auto & x : sample2)
cout << x.first << " : " << x.second << endl;
// swapping
sample1.swap(sample2);
cout << " Elements of maps after swap \n" ;
cout << " Elements of first map are : \n" ;
for ( auto & x : sample1)
cout << x.first << " : " << x.second << endl;
cout << " Elements of second map are : \n" ;
for ( auto & x : sample2)
cout << x.first << " : " << x.second << endl;
return 0;
} |
Elements of maps before swap Elements of first map are : 5 : 8 4 : 6 3 : 4 2 : 2 Elements of second map are : 14 : 15 26 : 17 12 : 13 10 : 11 Elements of maps after swap Elements of first map are : 14 : 15 26 : 17 12 : 13 10 : 11 Elements of second map are : 5 : 8 4 : 6 3 : 4 2 : 2
Example 2
// C++ code to illustrate the method // unordered_map swap #include <bits/stdc++.h> using namespace std;
int main()
{ unordered_map< char , int > sample1, sample2;
// Map initialization
sample1 = { { 'a' , 2 }, { 'b' , 4 }, { 'c' , 6 }, { 'd' , 8 } };
sample2 = { { 'e' , 11 }, { 'f' , 13 }, { 'h' , 15 } };
// printing details before calling swap
cout << " Elements of maps before swap \n" ;
cout << " Elements of first map are : \n" ;
for ( auto & x : sample1)
cout << x.first << " : " << x.second << endl;
cout << " Elements of second map are : \n" ;
for ( auto & x : sample2)
cout << x.first << " : " << x.second << endl;
// swapping
sample1.swap(sample2);
cout << " Elements of maps after swap \n" ;
cout << " Elements of first map are : \n" ;
for ( auto & x : sample1)
cout << x.first << " : " << x.second << endl;
cout << " Elements of second map are : \n" ;
for ( auto & x : sample2)
cout << x.first << " : " << x.second << endl;
return 0;
} |
Elements of maps before swap Elements of first map are : d : 8 c : 6 b : 4 a : 2 Elements of second map are : h : 15 f : 13 e : 11 Elements of maps after swap Elements of first map are : h : 15 f : 13 e : 11 Elements of second map are : d : 8 c : 6 b : 4 a : 2
Note : Caller and called unordered_map both should contain same type of elements otherwise we will get compile time error.