C++ map emplace_hint() function

C++ map emplace_hint() function is used to extend the map container by inserting new elements into the container using hint as a position for element. Elements are built directly (neither copied nor moved).

The constructor of the element is called by giving the arguments args passed to this function. Insertion takes place only if the key is not present already.

Syntax

template <class... Args>
    iterator emplace_hint (const_iterator position, Args&&...args);  //since C++ 11

Parameter

args: The arguments forwarded to construct an element to be inserted into the map.

position: Hint for the position to insert the new elements.

Return value

It returns an iterator to the newly inserted elements. If the element already exists, insertion is failed and returns an iterator to the existing element.

Example 1

Let's see a simple example to insert the elements into the map.

#include <iostream>
#include <map>
using namespace std;
int main(void) {
   map<char, int> m = {
            {'b', 20},
            {'c', 30},
            {'d', 40},
            };

   m.emplace_hint(m.end(), 'e', 50);
   m.emplace_hint(m.begin(), 'a', 10);
  cout << "Map contains following elements" << endl;
  for (auto it = m.begin(); it != m.end(); ++it)
  cout << it->first << " = " << it->second << endl;
   return 0;
}

Output:

Map contains following elements
a = 10
b = 20
c = 30
d = 40
e = 50

In the above example, it simply inserts the element into the map m with the given key value pairs and positions.

Example 2

Let's see a simple example.

#include <map>  
#include <string>  
#include <iostream>  
using namespace std;  
template <typename M> void print(const M& m) {  
 cout << m.size() << " elements: " << endl;  
 for (const auto& p : m) {  
 cout << "(" << p.first <<  "," << p.second << ") ";  
 }  
 cout << endl;  
}  
  
int main()  
{  
    map<string, string> m1;  
  
    // Emplace some test data  
    m1.emplace("Ram", "Accounting");  
    m1.emplace("Rakesh", "Accounting");  
    m1.emplace("Sunil", "Engineering");  
    cout << "map starting data: ";  
    print(m1);  
    cout << endl;  
   // Emplace with hint  
    // m1.end() should be the "next" element after this emplacement  
    m1.emplace_hint(m1.end(), "Deep", "Engineering");  
    cout << "map modified, now contains ";  
    print(m1);  
    cout << endl;  
} 

Output:

  map starting data: 3 elements: 
(Rakesh,Accounting) (Ram,Accounting) (Sunil,Engineering) 

map modified, now contains 4 elements: 
(Deep,Engineering) (Rakesh,Accounting) (Ram,Accounting) (Sunil,Engineering)

Example 3

Let's see a simple example to insert the elements into the map with the given position.

#include <iostream>
#include <map>
using namespace std;
int main ()
{
  map<char,int> mymap;
  auto it = mymap.end();

  it = mymap.emplace_hint(it,'b',10);
  mymap.emplace_hint(it,'a',12);
  mymap.emplace_hint(mymap.end(),'c',14);
 cout << "mymap contains:";
  for (auto& x: mymap)
    cout << " [" << x.first << ':' << x.second << ']';
    cout << '\n';

  return 0;
}

Output:

mymap contains: [a:12] [b:10] [c:14]

Example 4

Let's see a simple example to insert the element.

#include <iostream>
#include <map>
#include <string>
using namespace std;
int main() {
 typedef map<string, int> city;  
   string name;
   int age;
   city fmly ;
   int n;
  cout<<"Enter the number of fmly members :";
  cin>>n;
  cout<<"Enter the name and age of each member: \n";
   for(int i =0; i<n; i++)
   {
       cin>> name;      // Get key
       cin>> age;    // Get value

       fmly.emplace_hint(fmly.begin(),name,age);
       
   }
   
      cout<<"\nTotal memnber of fmly is:"<< fmly.size();

      cout<<"\nDetails of fmly members: \n";
      cout<<"\nName  |  Age \n ________________________\n";
      city::iterator p;
      for(p = fmly.begin(); p!=fmly.end(); p++)
      {
          cout<<(*p).first << " | " <<(*p).second <<" \n ";
      }
    
   return 0;
}

Output:

Enter the number of fmly members : 3
Enter the name and age of each member: 
Ram 42
Sita 37
Laxman 40

Total memnber of fmly is:3
Details of fmly members: 

Name    |  Age 
__________________________
Laxman | 40 
Ram      | 42 
Sita       | 37

In the above example, it simply inserts the elements by the user?s choice in the beginning of the map.

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