Map Emplace in C++ STL

In this article we will be discussing the working, syntax and examples of map::emplace() function in C++ STL.

What is a Map in C++ STL?

Maps are the associative container, which facilitates to store the elements formed by a combination of key value and mapped value in a specific order. In a map container the data is internally always sorted with the help of its associated keys. The values in the map container are accessed by its unique keys.

What is a map::emplace()?

The map::emplace( ) is a function which comes under <map> header file. This function constructs and inserts an element into the associated map container.

emplace() inserts the new element if the key of the element which is to be emplaced is unique. The insertion only happens if there is no element with the same key of the value which is to be inserted. This function works the same as insert() which copies and moves the existing object into the container.

If the element is successfully inserted the size of the container is increased by 1

Syntax

map_name.emplace(Args&& args);

Parameters

This function accepts the following parameter −

args − The arguments or values which we want to be emplaced or inserted.

Return value

If the insertion is successful then the function returns the iterator pointing to the new element which is inserted. Else it returns the iterator to equivalent value which is already present in the container.

Input

map<char, int> newmap;
emplace( ‘a’, 1);

Output

a

Example

 Live Demo

#include <bits/stdc++.h>
using namespace std;
int main() {
   map<int, int> TP_Map;
   TP_Map.emplace(4, 50);
   TP_Map.emplace(2, 30);
   TP_Map.emplace(1, 10);
   TP_Map.emplace(1, 20);
   TP_Map.emplace(1, 30);
   cout<<"TP Map is : \n";
   cout << "MAP_KEY\tMAP_ELEMENT\n";
   for (auto i = TP_Map.begin(); i!= TP_Map.end(); i++)
      cout << i->first << "\t" << i->second << endl;
   return 0;
}

Output

TP Map is:
MAP_KEY    MAP_ELEMENT
1             10
2             30
4             50