CODEWITHSUNDEEP
c++dictionaryoperator-overloading
VINOTH ENERGETIC
VINOTH ENERGETIC

Reputation: 1833

overloading of < operator not called when using struct as key in map?

I have understood that we have to write the operator overloading function for < operator when we have using the key as struct since the map uses the strict week ordering it has to compare before inserting in to map.

Hope my understanding is correct by reading from here.

consider the following snippet 

  struct Node
    {
       int a;     

     };


    // This is not called

  bool operator< (const Node &p_node1,const Node &p_node2)
  {
       printf("\nCALLED OPERATOR OVERLOADING");
       return true;
  }

    int main()
    {
       using namespace std;        
       map<Node,int> my_map;        
       Node n1;
       n1.a=55;

       my_map[n1]=2; // operator overloading should be called

       return 0;
    }

And the issue is operator overloading function not called?

EDIT:

From the answer below, After adding the one more pair to container operator overloading is called. But why it is called three times specifically, what is compared here?

Upvotes: 2

Views: 222

Answers (3)

shivakumar
shivakumar

Reputation: 3387

Have atleast 2 elements in map for comparison operator to be called.

       Node n1;
       n1.a=55;

       my_map[n1]=2; // operator overloading should be called

       Node n2;
       n2.a=55;

       my_map[n2]=3;

See below modified example code.

http://ideone.com/iGY9Xa

Upvotes: 0

Ivaylo Strandjev
Ivaylo Strandjev

Reputation: 70931

You are inserting the only element in an empty map and so the comparison operator is never called. Try having more than one element in my_map.

Upvotes: 2

ebasconp
ebasconp

Reputation: 1638

When the map is empty, the comparator does not need to be invoked because there is nothing to compare against to.

Upvotes: 6

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