Question

When I add a Retreive() method to my BST implementation I get a “unresolved external” compiler error.

The Retrieve() member function checks to see whether the value entered by the user exists in the BST, and if it does sets found = false.

//Header File
using namespace std;

struct PersonRec
{
    char name[20];
    int bribe;
    PersonRec* leftLink;
    PersonRec* rightLink;
};


class CTree
{

private:
    PersonRec *tree;
    bool IsEmpty();
    void AddItem( PersonRec*&, PersonRec*);
    void DisplayTree(PersonRec*);
    void Retrieve(PersonRec*, PersonRec*,bool&);

public:
    CTree();
    //~CTree();
    void Add();
    void View();

};




//Implementation File
#include <iostream>
#include <string>

using namespace std;

#include "ctree.h"

CTree::CTree()
{
    tree = NULL;
}

//PersonList::~MyTree()
//{
//
//}


bool CTree::IsEmpty()
{
    if(tree == NULL) 
    {
        return true;
    }
    else
    {
        return false;
    }
}

void CTree::Add()
{
    PersonRec* newPerson = new PersonRec();
    cout << "Enter the person's name: ";
    std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
    cin.getline(newPerson->name, 20);
    cout << "Enter the person's contribution: ";
    cin >> newPerson->bribe;
    bool found = false;


    newPerson->leftLink = NULL;
    newPerson->rightLink = NULL;

    Retrieve(tree, newPerson, found);
     if (found)
         cout << "Bribe allready entered\n";
     else
         AddItem(tree, newPerson);
}

void CTree::View()
{
    if (IsEmpty())
    {
        cout<<"The list is empy";
    }
    else
    {
        DisplayTree(tree);

    }

};

void CTree::AddItem( PersonRec*& ptr, PersonRec* newPer )
{
        if (ptr == NULL)
        {
            ptr = newPer;
        }
        else if ( newPer->bribe < ptr->bribe)
            AddItem(ptr->leftLink, newPer); 
        else
            AddItem(ptr->rightLink, newPer); 
}
void CTree::DisplayTree(PersonRec* ptr)
{
    if (ptr == NULL)
                    return;
    DisplayTree(ptr->rightLink);
    cout<<ptr->name<<" "<<"$"<<ptr->bribe <<endl;
    DisplayTree(ptr->leftLink); 
}
void Retrieve(PersonRec*& ptr, PersonRec* newPer, bool& found)
{
    {
        if (ptr == NULL)
        {
            found = false; // item is not found.
        }
        else if ( newPer->bribe < ptr->bribe)
        {
            Retrieve(ptr->leftLink, newPer, found);
        }
             // Search left subtree.
        else if (newPer->bribe > ptr->bribe)
        {
            Retrieve(ptr->rightLink, newPer, found);// Search right subtree.
        }   
        else
        {
            //newPer.bribe = ptr->info; // item is found.
            found = true;
        }
    }
}
//Driver File
#include <iostream>

using namespace std;
#include <cstdlib>
#include "ctree.h"

int displayMenu (void);
void processChoice(int, CTree&);

int main (void)
{
int num;
CTree ct;
do 
{
num = displayMenu();
if (num != 3)
processChoice(num, ct);
} while (num != 3);
return 0;
}

int displayMenu (void)
{
int choice;
cout << "\nMenu\n";
cout << "==============================\n\n";
cout << "1. Add student to waiting list\n";
cout << "2. View waiting list\n";
cout << "3. Exit program\n\n";
cout << "Please enter choice: ";
cin >> choice;
return choice;
}

void processChoice(int choice, CTree& myTree)
{
   switch (choice)
   {
      case 1: myTree.Add (); break;
      case 2: myTree.View (); break;
   } 
}

Answer 1

You don’t qualify the definition with the class name:

void Retrieve(PersonRec*& ptr, PersonRec* newPer, bool& found)

should be

void CTree::Retrieve(PersonRec* ptr, PersonRec* newPer, bool& found)