Map vs Unordered Map in STL in C++
About Map and Unordered Map
Map and Unordered Map in STL are containers which is used to store elements in key-value pair in the particular order.
Map in STL :
Definition
Map in stl is defined as the container which store the elements in key-value pair in sorted order.
Unordered Map in STL :
Definition
Unordered Map in stl is defined as the container which store the elements in key-value pair in non-sorted order.
Important Note
- The items are stored in mapped way in associative containers called maps.
- There are key values and mapped values for every element.
- The key values for any two mapped values cannot be the same.
- An associated container called unordered map holds elements created by fusing a mapped value with a key value.
- The element is uniquely identified by the key value, and the mapped value is the content related to the key.
Difference in Map and Unordered Map :
| Map | Unordered Map |
|---|---|
| Elements are ordered in increasing order | Elements are not ordered in the sorted order. |
| Implementation is done by BST | Implementation is done by Hashtable. |
| It is slow | It is fast. |
| Used when ordering is required | Used when no ordering is required. |
Example of Map in STL :
Run
#include<iostream>
#include<bits/stdc++.h>
using namespace std;
int main() {
map< int,int> mpp;
mpp.insert({1,10});
mpp.insert({2,20});
mpp.insert({4,40});
mpp.insert({8,80});
mpp.insert({6,60});
mpp.insert({3,30});
cout<<"The key and value in the map : "<< endl;
for(auto it : mpp){
cout<< it.first<<" "<< it.second<< endl;
}
cout<< endl;
cout<<"The size of map :"<< mpp.size();
return 0;
}
Output :
The key and value in the map : 1 10 2 20 3 30 4 40 6 60 8 80 The size of map :6
In the above program, we take the map insert the key and value in it, when we print them , key will output in the sorted order.
Example of Unordered Map in STL:
Run
#include<iostream>
#include<bits/stdc++.h>
using namespace std;
int main() {
unordered_map< int,int> mpp;
mpp.insert({1,10});
mpp.insert({2,20});
mpp.insert({4,40});
mpp.insert({8,80});
mpp.insert({6,60});
mpp.insert({3,30});
cout<<"The key and value in the map : "<< endl;
for(auto it : mpp){
cout<< it.first<<" "<< it.second<< endl;
}
cout<< endl;
cout<<"The size of map :"<< mpp.size();
return 0;
}
Output :
The key and value in the map : 3 30 6 60 8 80 4 40 2 20 1 10 The size of map :6
In the above program, we take the map insert the key and value in it, when we print them ,it is not necessary that key will output in the sorted order.
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