Question

I’m constructing a generic binary tree which includes a struct, TreeNode. I implement a function rootPtr() which returns the pointer to the root of the tree. binarytree.h is simply the following:

template <class T>
class BinaryTree {
public:

typedef struct TreeNode {
    T item;
    TreeNode *leftChildPtr; // pointer to left child
    TreeNode *rightChildPtr;

public:
    TreeNode(const T& nodeItem,
            TreeNode *left,
            TreeNode * right)
    : item(nodeItem), leftChildPtr(left), rightChildPtr(right) {
    }

    TreeNode(const T & nodeItem)
    : item(nodeItem) {
        leftChildPtr = NULL;
        rightChildPtr = NULL;
    }
  } TN; //end treenode

//Function prototype
TN* rootPtr() const;

private:
    TN *root;

} //end binarytree

This is the snippet from binarytree.cpp which results error.

template <class T>
BinaryTree<T>::TN* BinaryTree<T>::rootPtr() {
    return root;
}

Compiler complains error: expected constructor, destructor, or type conversion before ‘*’ token
I’ve seen this error before and handled it by using like BinaryTree:: but this time since it’s generic, I don’t know what should I do. Any help would be appreciated.

Answer 1

Simplified rule of thumb: you cannot define member functions when the class has a template in a separate cpp file. Try putting that together with the class definition, on the header 😉