Doug - 4 months ago 30

C++ Question

`template <class T>`

bool BST<T>::search(const T& x, int& len) const

{

return search(BT<T>::root, x);

}

template <class T>

bool BST<T>::search(struct Node<T>*& root, const T& x)

{

if (root == NULL)

return false;

else

{

if (root->data == x)

return true;

else if(root->data < x)

search(root->left, x);

else

search(root->right, x);

}

}

So this is my search function for my BST class with a T node. x is the data being searched for within the tree, len is just the amount of nodes it has to travel to come up with the matching node if it exists. I have not implented that yet, I'm just incrementally developing my assignment. I'm calling it by doing this:

`if(t.search(v[1], len) == true)`

cout << endl << "true";

v is just a vector I had to create to compare it to, and so this is just supplying it with an int. The error I'm getting:

`BST.h: In member function âbool BST<T>::search(const T&, int&) const [with T = int]â:`

prog5.cc:24: instantiated from here

BST.h:78: error: no matching function for call to âBST<int>::search(Node<int>* const&, const int&) constâ

BST.h:76: note: candidates are: bool BST<T>::search(const T&, int&) const [with T = int]

BST.h:83: note: bool BST<T>::search(Node<T>*&, const T&) [with T = int]

So I'm not sure what I'm doing wrong or where I'm doing wrong.

Answer

Okay, `bool BST<T>::search(struct Node<T>*& root, const T& x)`

should probably have const after it like so: `bool BST<T>::search(struct Node<T>*& root, const T& x) const`

. Basically, you've called a non-const function from a const function and this is a no-no.

BTW, this looks suspect to me "`struct Node<T>*&`

"... I'd probably drop the & and work with `Node<T>*`

... but maybe you need that because of the *struct*?

Also, this is C++, there is no reason to leave Node as a struct... needing to have **struct** in the parameter definition just looks bad, IMHO. Why not make Node a class?