Question

My header file for a basic binary tree includes the following:

template<typename T>
    class Btree{
        // OVERVIEW:    a binary tree with flexible structure that is not sorted

    private:

        struct node {           //a container object 
            node *left;     //left and right tree
            node *right;
            T *o;       // pointer to  object of node
        };

    public:

        node *root; //pointer to the root of the tree (NULL if empty)

        node* insert (node *parent, T *child, int child);
        //MODIFIES: this
        //EFFECTS:  creates a node that stores a pointer to the new child 
        //      and returns the pointer to the node of the new child    
        //      the integer child is either 0, for left child,
        //      or anything else for right child    

            //  void printTree (node * root);
        //EFFECTS:  takes the root of a tree and prints the tree's 
        //      coordinates  

        Btree(){};  //ctor
        Btree(){}   //dtor


    };

    #include "btree.cpp"

My .cpp looks like this, and note that it is included at the bottom of my header to avoid template compiler errors:

   template <typename T>
    Btree<T> :: node * Btree<T>::insert (node *parent, T *child, int child)

    {
        node *np = new node;
        np-> o = child; 
        np->left = NULL;
        np->right  = NULL;
        if (child == 0)
            parent->left = np;
        else
            parent->right = np;
        return np;
    } 

however, I get the following compiler error:

btree.cpp:3: error: expected constructor, destructor, or type conversion before ‘*’ token

I’m compiling with g++, version 4.1.2.

Can anyone help?

Answer 1

First of all, your destructor should have a ~ in front of it, so change

Btree();    //ctor
Btree(){}   //dtor

to

Btree();    //ctor
~Btree(){}   //dtor

Second, you need typename before the return type of insert because it is a dependent type:

   template <typename T>
   typename Btree<T>::node* Btree<T>::insert(node *parent, T *child, int child)
// ^^^^^^^^ <- needed
   {
    node *np = new node;
    np-> o = child; 
    np->left = NULL;
    np->right  = NULL;
    if (child == 0)
        parent->left = np;
    else
        parent->right = np;
    return np;
   } 

Also you need to rename one of your arguments, you have two named child.