Question

i created a stuct which contains one character and one string

 struct M2E
 { char english;
 string morse;}

by using code given by, i created a binary tree of M2E which is bintree
but i want to sort these M2Es in string morse order(“*” less than “-“)
so i did a operater overloading in struct M2E

 bool operator == (M2E& other) const
{
    return morse.compare(other.morse);
}

but i keep giving the following error message when im compling

no match for "operator ==" in ((binNode<M2E>*)this)->binNode<M2E>::nodeData == dataItem
note:candidates are :bool M2E::operator==(M2E&) const

the code i am using for binary tree which is bintree.h is:

  template <typename dataType> class bintree
{  
  private:
  binNode<dataType> *root;
  int numItems;

  void insert(const dataType& newData) 
  {
     // insert the newData into the tree

     if (root == NULL) 
     {
        root = new binNode<dataType>(newData);
     } 
     else 
     {
        root->insert(root, newData);
     }
     numItems++;
  }

the code im using for binary node which is binnode.h is:

  template <typename dataType> class binNode 
 {
 private:
  // private data ====================================
  dataType nodeData;
  binNode<dataType> *left, *right;

        void insert(binNode<dataType>* &root, const dataType& dataItem) 
  {
     if (nodeData == dataItem) 
     {
        throw std::invalid_argument("dataItem already in tree");
     }

     if (dataItem < nodeData) 
     {
        if (left == NULL) 
        {
           left = new binNode(dataItem);
        } 
        else 
        {
           left->insert(left, dataItem);
        }
     } 
     else 
     {
        if (right == NULL) 
        {
           right = new binNode(dataItem);
        } 
        else 
        {
           right->insert(right, dataItem);
        }
     }
     rebalance(root);
  }

thx for helping

Answer 1

The problem is that you are taking a const datatype dataItem in insert(), but the operator== takes a non-const M2E parameter.

You need to specify the operator== parameter type to be const:

bool operator == (const M2E& other) const {
  //...
}

Remember that const is a contract: the function promises not to change the value of its parameter. So insert() makes this promise, but operator== does not, so insert() cannot make that operator call it as-is. By adding the const to operator==‘s parameter type, you make operator== make the same promise, so insert() can call it