c++ template binary search tree - c++

Question

What I want is a rather simple binary search tree that via the template tag, allows for any numerical data to be used within it, but I'm having some rather obnoxious issues that I have no clue of how to get rid off, if anyone can help, it would be much appreciated. The error message that keeps popping up for me is "Invalid use of template-name 'BST' without an argument list" - and quite frankly I have no clue how to solve it. It occurs on line 31, 89, 105, 120, 130, 141 in the bst.cpp file:
Main.cpp
#include <iostream>
#include "bst.h"
using namespace std;
int main()
{
BST <int> tree;
tree.insert(8);
tree.insert(25);
tree.insert(99);
tree.insert(20);
tree.insert(25);
tree.insert(20);
tree.insert(2);
tree.insert(89);
tree.insert(15);
tree.insert(10);
tree.insert(30);
tree.insert(50);
tree.displayorder();
int number;
int Inputnumber;
while (true){
cout << "Choose what you want to do: " << endl << "1# Insert" << endl << "2# Display Orders" << endl << "3# Search" << endl << "4# Delete" << endl << endl << endl;
cin >> Inputnumber;
if (Inputnumber==1){
cout << endl << "Enter the number you want inserted: ";
cin >> number;
tree.insert(number);
cout << endl << endl << endl;
}
if (Inputnumber==2){
cout<<"Display Orders: " << endl;
tree.displayorder();
cout << endl << endl << endl;
}
if (Inputnumber==3){
cout<<"Enter the number you want to search for: ";
cin >> number;
tree.search(number);
cout << endl << endl << endl;
}
if (Inputnumber==4){
cout << "Enter the number you want to remove: ";
cin >> number;
tree.remove(number);
cout << endl << endl << endl;
}
}
}
bst.h
#ifndef BST_H
#define BST_H
template <class T>
class BST
{
struct node
{
T data;
node* left;
node* right;
};
node* root;
node* makeEmpty(node* tree);
node* insert(T x, node* tree);
node* findMin(node* tree);
node* findMax(node* tree);
node* remove(T x, node* tree);
void inorder(node* tree);
void preorder(node* tree);
void postorder(node* tree);
public:
BST();
~BST();
node* find(node* tree, T x);
void insert(T x);
void remove(T x);
void displayorder();
void search(T x);
};
#endif // BST_H
bst.cpp
#include <iostream>
#include "bst.h"
using namespace std;
template <class T>
void BST<T>::preorder(node* tree)
{
if(tree == NULL){
return;
}
cout << tree->data << " ";
inorder(tree->left);
inorder(tree->right);
}
template <class T>
void BST<T>::postorder(node* tree)
{
if(tree == NULL){
return;
}
inorder(tree->left);
inorder(tree->right);
cout << tree->data << " ";
}
template <typename T>
BST::node* BST<T>::find(node* tree, T x) //AN ERROR OCCURS HERE
{
if(tree == NULL)
return NULL;
else if(x < tree->data)
return find(tree->left, x);
else if(x > tree->data)
return find(tree->right, x);
else
return tree;
}
template <typename T>
BST<T>::BST()
{
root = NULL;
}
template <typename T>
BST<T>::~BST()
{
root = makeEmpty(root);
}
template <class T>
void BST<T>::insert(T x)
{
root = insert(x, root);
}
template <class T>
void BST<T>::remove(T x)
{
root = remove(x, root);
}
template <class T>
void BST<T>::displayorder()
{
inorder(root);
cout << endl;
preorder(root);
cout << endl;
postorder(root);
cout << endl << endl;
}
template <class T>
void BST<T>::search(T x)
{
if(root = find(root, x)){
cout << endl << "Found!" << endl;
}
else{
cout << endl << "Not Found!" << endl;
}
}
template <class T>
BST::node* BST<T>::makeEmpty(node* tree) //AN ERROR OCCURS HERE
{
if(tree == NULL)
return NULL;
{
makeEmpty(tree->left);
makeEmpty(tree->right);
delete tree;
}
return NULL;
}
template <class T>
BST::node* BST<T>::insert(T x, node* tree) //AN ERROR OCCURS HERE
{
if(tree == NULL)
{
tree = new node;
tree->data = x;
tree->left = tree->right = NULL;
}
else if(x < tree->data)
tree->left = insert(x, tree->left);
else if(x >= tree->data)
tree->right = insert(x, tree->right);
return tree;
}
BST::node* BST::findMin(node* tree) //AN ERROR OCCURS HERE
{
if(tree == NULL)
return NULL;
else if(tree->left == NULL)
return tree;
else
return findMin(tree->left);
}
BST::node* BST::findMax(node* tree) //AN ERROR OCCURS HERE
{
if(tree == NULL)
return NULL;
else if(tree->right == NULL)
return tree;
else
return findMax(tree->right);
}
template <typename T>
BST::node* BST<T>::remove(T x, node* tree) //AN ERROR OCCURS HERE
{
node* temp;
if(tree == NULL)
return NULL;
else if(x < tree->data)
tree->left = remove(x, tree->left);
else if(x > tree->data)
tree->right = remove(x, tree->right);
else if(tree->left && tree->right)
{
temp = findMin(tree->right);
tree->data = temp->data;
tree->right = remove(tree->data, tree->right);
}
else
{
temp = tree;
if(tree->left == NULL)
tree = tree->right;
else if(tree->right == NULL)
tree = tree->left;
delete temp;
}
return tree;
}
template <class T>
void BST<T>::inorder(node* tree)
{
if(tree == NULL){
return;
}
inorder(tree->left);
cout << tree->data << " ";
inorder(tree->right);
}

Answer 1

You need to qualify BST::node too, as BST<T>::node. Also, keep in mind that all the template code will need to live in bst.h because it will need to be instantiated by each source file that uses it (like main.cpp).

Answer 2

Add the
Add the BST::node in your function definitions. In addition include the .ipp (cpp file) as shown in line 27 in order to have the class methods in the header and the implementation in a .ipp file. You don't have to place all your template code in the header file if you don't wan't to.
Another tip is the fact that you must not pass the root node to your functions because anyone outside the class can have access to your tree root. Aim for something like the following code
1 #ifndef BST_H
2 #define BST_H
3
4 #include <memory>
5
6 template<typename T>
7 class node;
8
9 template <typename T>
10 class BST
11 {
12 public:
13 BST();
14 BST(std::initializer_list<T> init);
15 ~BST();
16
17 void make_empty();
18 bool is_empty() const noexcept;
19 bool is_full() const;
20 void insert(const T&);
21 void remove(const T&);
22 void print_tree() const noexcept;
23 private:
24 std::unique_ptr<node<T>> root;
25 };
26
27 #include "binary_search_tree.ipp"
28
29 #endif