INTRODUCTION
UNORDERED MULTIMAP in Cpp
In this tutorial, we are going to learn about the unordered multimap container in the standard template library of C++ programming language. An unordered multimap is an associative container that stores items consisting of key-value pairs. The unordered multimap is almost similar to an unordered_map except for permitting the repeated values.
The syntax of the unordered multimap is as follows
Unordered_multimap< key_datatype , mapped_datatype > var_name;Where key_datatype and mapped_datatype represent the data types of the key_value and the mapped_value respectively.
Let’s look at some of the properties of the unordered_multimap.
- The unordered_multimap store non-unique key-value pairs.
- There is no specific order in storing the items in the unordered_multimap.
- The unordered_multimap implements the hash table.
- The items with the same key in the unordered_multimap are grouped together in the same bucket.
These are some of the properties of the unordered_multimap.
Let’s look at some of the basic methods that are performed on the unordered_multimaps.
insert(): this method adds a new item to the unordered_multimap in a specific order
erase(): this method removes the particular item from the unordered_multimap.
begin(): this method returns an iterator to the first element in the unordered_multimap.
end(): this method returns an iterator to the last element in the unordered_multimap.
count(): this method is used to return the number of items stored in the unordered_multimap.
empty(): this method returns a boolean value whether the particular unordered_multimap is empty or not.
clear(): this method is used to remove all the elements from the unordered_multimap and empty it.
These are some of the basic methods that are implemented on the unordered_multimap container.
Let’s look at a sample program implementing unordered_multimaps
#include <iostream>
#include <string>
#include <unordered_map>
using namespace std;
int main() {
unordered_multimap <string, int> m1;
m1 = { {"stephen",98} , {"alice",89}};
m1.insert ( {{"robert",77} , {"william",100}} );
pair < string, int> hit2 ("steve",95);
m1.insert (hit2);
m1.insert (make_pair <string, int> ("steve",91));
cout << "Unordered multimap contains: " << endl;
unordered_multimap <string, int> :: iterator itr;
for (itr= m1.begin(); itr!= m1.end(); ++itr) {
cout<<(*itr).first<<"\t"<<(*itr).second<<endl;
}
cout << "\nErasing first pair " << endl;
m1.erase (m1.begin());
for (itr= m1.begin(); itr!= m1.end(); ++itr) {
cout<<(*itr).first<<"\t"<<(*itr).second<<endl;
}
cout<<"\nsize of the unordered_multimap is : \n"<<m1.size()<<endl;
m1.clear();
cout << "\nChecking the state of the Unordered multimap:" << endl;
if (m1.empty())
cout << "Unordered multi map is empty " << endl;
else
cout << "Unordered multi map is not empty " << endl;
return 0;
}
The output of the program is.
In the above program,
- we created a unordered_multimap and inserted the items consisting of string keys and integer-mapped values by using different methods.
- After inserting the items into the unordered_multimap, we created an iterator to traverse over the unordered_multimap.
- We removed an item from the unordered_multimap by using the erase() method. We calculated the number of elements in the unordered_multimap by using the size() method.
- After implementing all the basic operations, we removed all the items from the unordered_multimap by using the clear() method.
This is the implementation of the unordered_multimap.
CONCLUSION
That’s it from this tutorial. We have learned about the unordered_multimap container, its properties, basic methods that are implemented on unordered_multimaps and differences between the unordered_multimaps and the multimaps. Hope you guys found it interesting. Happy Coding!
