Question

hI, I’m trying to get this code from Larry Nyhoff’s book to compile in Bloodshed. It’s actually been taken word for word from the author’s website, though I declared it on .cpp instead of .h (the .h file ain’t working with the tester application).

http://cs.calvin.edu/activities/books/c++/ds/2e/SourcePrograms/Chap12/

The search(const DataType & item) function is what’s giving me grief. The compiler error says:

In member function `bool BST<DataType>::search(const DataType&) const':  expected `;' before 'locptr'  `locptr' undeclared (first use this function)  

What I’m I missing here?

 #include <iostream>  #ifndef BINARY_SEARCH_TREE #define BINARY_SEARCH_TREE   template <typename DataType> class BST {  public:   /***** Function Members *****/   BST();    bool empty() const;    bool search(const DataType & item) const;    void insert(const DataType & item);    void remove(const DataType & item);    void inorder(std::ostream & out) const;    void graph(std::ostream & out) const;    private:   /***** Node class *****/   class BinNode    {    public:     DataType data;     BinNode * left;     BinNode * right;      // BinNode constructors     // Default -- data part is default DataType value; both links are null.     BinNode()     : left(0), right(0)     {}      // Explicit Value -- data part contains item; both links are null.     BinNode(DataType item)     : data(item), left(0), right(0)     {}   }; //end inner class  typedef BinNode * BinNodePointer;     /***** Private Function Members *****/   void search2(const DataType & item, bool & found,                BinNodePointer & locptr, BinNodePointer & parent) const;  /*------------------------------------------------------------------------    Locate a node containing item and its parent.     Precondition:  None.    Postcondition: locptr points to node containing item or is null if         not found, and parent points to its parent.#include <iostream>  ------------------------------------------------------------------------*/    void inorderAux(std::ostream & out,                    BST<DataType>::BinNodePointer subtreePtr) const;   /*------------------------------------------------------------------------     Inorder traversal auxiliary function.      Precondition:  ostream out is open; subtreePtr points to a subtree          of this BST.     Postcondition: Subtree with root pointed to by subtreePtr has been         output to out.  ------------------------------------------------------------------------*/    void graphAux(std::ostream & out, int indent,                       BST<DataType>::BinNodePointer subtreeRoot) const;   /*------------------------------------------------------------------------     Graph auxiliary function.      Precondition:  ostream out is open; subtreePtr points to a subtree          of this BST.     Postcondition: Graphical representation of subtree with root pointed          to by subtreePtr has been output to out, indented indent spaces.  ------------------------------------------------------------------------*/   /***** Data Members *****/   BinNodePointer myRoot;   }; // end of class template declaration  //--- Definition of constructor template <typename DataType> inline BST<DataType>::BST() : myRoot(0) {}  //--- Definition of empty() template <typename DataType> inline bool BST<DataType>::empty() const { return myRoot == 0; }  //--- Definition of search() template <typename DataType> bool BST<DataType>::search(const DataType & item) const {    BST<DataType>::BinNodePointer locptr = myRoot; //**THIS FAILS, WHY?**//    bool found = false;    while (!found && locptr != 0)    {       if (item < locptr->data)       // descend left         locptr = locptr->left;       else if (locptr->data < item)  // descend right         locptr = locptr->right;       else                           // item found         found = true;    }    return found; }     #endif 

Answer 1

Put a typename before the declaration:

typename BST<DataType>::BinNodePointer locptr = myRoot; 

The point is that due to potential template specialization, the compiler cannot know that the dependent identifier BinNodePointer identifies a type.