C++ unordered_multimap - insert() Function
The C++ unordered_multimap::insert function is used to insert new elements in the container. This results into increasing the unordered_multimap size by the number of elements inserted.
Syntax
//single element version iterator insert (const value_type& val); template <class P> pair<iterator,bool> insert (P&& val); //single element with hint version iterator insert (const_iterator position, const value_type& val); template <class P> iterator insert (const_iterator position, P&& val); //range version template <class InputIterator> void insert (InputIterator first, InputIterator last); //initializer list version void insert (initializer_list<value_type> il);
Parameters
position |
Specify the hint for the position where the element can be inserted. |
val |
Specify the value to be copied (or moved) to the inserted elements. |
first |
Specify the starting position of InputIterator. Copies of the elements in the range [first,last) are inserted in the container. |
last |
Specify the last position of InputIterator. Copies of the elements in the range [first,last) are inserted in the container. |
il |
Specify the initializer_list object. |
Return Value
Returns an iterator pointing to newly inserted element in the unordered_multimap.
Time Complexity
- Single element insertion: Average case - constant i.e, Θ(1). Worst case - linear i.e, Θ(n).
- Multiple elements insertion: Average case - linear in number of elements inserted. Worst case - quadratic: number of elements inserted multiplied by (container size + 1).
Example:
In the example below, the unordered_multimap::insert function is used to insert elements in the given unordered_multimap.
#include <iostream>
#include <unordered_map>
using namespace std;
int main (){
unordered_multimap<string, string> uMMap;
unordered_multimap<string, string>::iterator it;
//populating multimap
uMMap.insert(pair<string, string>("CAN", "Montreal"));
uMMap.insert(pair<string, string>("IND", "Mumbai"));
uMMap.insert(pair<string, string>("USA", "New York"));
cout<<"uMMap contains: \n ";
for(it = uMMap.begin(); it != uMMap.end(); ++it)
cout<<it->first<<" "<<it->second<<"\n ";
//insert single element in the multimap
uMMap.insert(pair<string, string>("IND", "Delhi"));
cout<<"\nuMMap contains: \n ";
for(it = uMMap.begin(); it != uMMap.end(); ++it)
cout<<it->first<<" "<<it->second<<"\n ";
//insert single element with hint in the multimap
it = uMMap.begin();
uMMap.insert(it, pair<string, string>("USA", "Washington"));
cout<<"\nuMMap contains: \n ";
for(it = uMMap.begin(); it != uMMap.end(); ++it)
cout<<it->first<<" "<<it->second<<"\n ";
return 0;
}
The output of the above code will be:
uMMap contains: USA New York IND Mumbai CAN Montreal uMMap contains: USA New York IND Delhi IND Mumbai CAN Montreal uMMap contains: USA New York USA Washington IND Delhi IND Mumbai CAN Montreal
Example:
A range of elements can also be inserted into a unordered_multimap. Consider the example below.
#include <iostream>
#include <unordered_map>
using namespace std;
int main (){
unordered_multimap<string, string> uMMap1;
unordered_multimap<string, string> uMMap2;
unordered_multimap<string, string>::iterator it;
//populating uMMap1
uMMap1.insert(pair<string, string>("CAN", "Montreal"));
uMMap1.insert(pair<string, string>("IND", "Mumbai"));
uMMap1.insert(pair<string, string>("USA", "New York"));
//populating uMMap2
uMMap2.insert(pair<string, string>("IND", "Delhi"));
uMMap2.insert(pair<string, string>("USA", "Washington"));
cout<<"uMMap1 contains: \n ";
for(it = uMMap1.begin(); it != uMMap1.end(); ++it)
cout<<it->first<<" "<<it->second<<"\n ";
//inserts a range of elements from uMMap2 to uMMap1
uMMap1.insert(uMMap2.begin(), uMMap2.end());
cout<<"\nuMMap1 contains: \n ";
for(it = uMMap1.begin(); it != uMMap1.end(); ++it)
cout<<it->first<<" "<<it->second<<"\n ";
return 0;
}
The output of the above code will be:
uMMap1 contains: USA New York IND Mumbai CAN Montreal uMMap1 contains: USA Washington USA New York IND Delhi IND Mumbai CAN Montreal
Example:
Similarly, the initializer list version can be used to insert elements in the given unordered_multimap.
#include <iostream>
#include <unordered_map>
using namespace std;
int main (){
unordered_multimap<string, string> uMMap;
unordered_multimap<string, string>::iterator it;
//populating uMMap
uMMap.insert(pair<string, string>("CAN", "Montreal"));
uMMap.insert(pair<string, string>("IND", "Mumbai"));
uMMap.insert(pair<string, string>("USA", "New York"));
cout<<"uMMap contains: \n ";
for(it = uMMap.begin(); it != uMMap.end(); ++it)
cout<<it->first<<" "<<it->second<<"\n ";
//insert elements of initializer list into multimap
initializer_list<pair<const string, string>> ilist =
{{"IND", "Delhi"}, {"USA", "Washington"}};
uMMap.insert(ilist);
cout<<"\nuMMap contains: \n ";
for(it = uMMap.begin(); it != uMMap.end(); ++it)
cout<<it->first<<" "<<it->second<<"\n ";
return 0;
}
The output of the above code will be:
uMMap contains: USA New York IND Mumbai CAN Montreal uMMap contains: USA Washington USA New York IND Delhi IND Mumbai CAN Montreal
❮ C++ <unordered_map> Library
