c++ virtual functions with Linked List - c++

Question

I'm running into some problems while trying to use a virtual function within my classes.
I'm using a Linked List to store Employee, Staff and Managers - which inherit each other (Staff and Managers inherit Employee base class).
I need to be able to access a function called getType which returns either "Staff Member" or "Manager" based on which class it is.
this snipit of code is my creation of staff and managers.
Staff staff4 = { "Lisa", "22/02/2012", 0004, HR, 8.9, 34.50 };
Employee* pStaff4 = &staff4;
Employee& testStaff4 = staff4;
myList->addInFront(testStaff4);
Staff staff5 = { "Jade", "23/03/2014", 0003, HR, 6.4, 38.50 };
Employee* pStaff5 = &staff5;
Employee& testStaff5 = staff5;
myList->addInFront(testStaff5);
Manager manager1 = { "Lily", "01/09/2012", 0001, MARKETING, 75968 };
Employee* pMan1 = &manager1;
Employee& testMan1 = manager1;
myList->addInFront(testMan1);
Manager manager2 = { "Craig", "27/03/2011", 0002, HR, 82478 };
Employee* pMan2 = &manager2;
Employee& testMan2 = manager2;
myList->addInFront(testMan2);
//cout << pStaff5->getType();
//system("pause");
This is my employee.h (i've taken out other functions to save space on this post)
class Employee
{
protected:
string name;
string startDate;
unsigned long empNumber;
string dept;
public:
Employee() {};
Employee(string, string, unsigned long, string);
virtual const string getType()
{
return "Emp";
}
};
class Manager : public Employee
{
private:
unsigned long salary;
public:
virtual const string getType()
{
return "Manager";
}
};
class Staff : public Employee
{
private:
float hourlyRate;
float hoursPerWeek;
public:
const string getType()
{
return "Staff Member";
}
};
and finally this is how i'm attempting to call the getType() function:
void displayList(const List& list)
{
List temp(list);
while (!temp.isEmpty())
{
cout << temp.first()->item.getType() << "\n";
cout << temp.first()->item.getName() << "\n";
temp.deleteFirst();
}
}
Here is my list header and .cpp
list.h
//#include <string>
#include "Employees.h"
#define Item Employee
using namespace std;
struct Node
{
Item item;
Node* next;
};
class List
{
private:
Node* head;
Node* end() const;
void copy(const List&);
void destroy();
public:
List();
List(const List&);
~List();
List& operator=(const List&);
bool operator==(const List&);
bool isEmpty() const;
Node* first() ;
Item last() const;
List tail() const;
void addInFront(const Item&);
void addAtEnd(const Item&);
void deleteFirst();
Node* search(const long);
bool searchDelete(const long);
};
list.cpp
#include "stdafx.h"
#include "List.h"
#include <assert.h>
List::List()
{
head = NULL;
}
List::List(const List& otherList) : head(nullptr)
{
copy(otherList);
}
bool List::isEmpty() const
{
return (head == nullptr);
}
Node* List::first()
{
assert(head != nullptr);
return head;
}
void List::deleteFirst()
{
if (head != NULL)
{
Node* tmp = head->next;
delete head;
head = tmp;
}
}
void List::addInFront(const Item& data)
{
Node* nodePtr = new Node;
assert(nodePtr != nullptr);
nodePtr -> item = data;
nodePtr ->next = head;
head = nodePtr;
}
Node* List::search(const long longID)
{
}
bool List::searchDelete(const long longID)
{
Node *temp, *prevNode;
temp = head;
prevNode = NULL;
while (temp != NULL)
{
}
}
Node* List::end() const
{
if (head == nullptr)
return nullptr;
else
{
Node* nodePtr = head;
while (nodePtr->next != nullptr)
{
nodePtr = nodePtr->next;
}
return nodePtr;
}
}
void List::addAtEnd(const Item& data)
{
Node* nodePtr = new Node;
assert(nodePtr != nullptr);
if (head == nullptr)
{
head = nodePtr;
nodePtr->item = data;
}
else
{
nodePtr->item = data;
Node* ptr = end();
ptr->next = nodePtr;
}
}
List& List::operator=(const List& rhs)
{
if (&rhs != this)
{
destroy();
copy(rhs);
}
return *this;
}
void List::copy(const List& otherList)
{
}
void List::destroy()
{
while (head != nullptr)
{
Node* ptr = head;
head = head->next;
delete ptr;
}
}
List::~List()
{
}
apologies about the length of these files.
I'm confused as to why it won't call the appropriate virtual function, as you can see in the first code snipit that i used pStaff5->getType() and that worked - however I can't access the nodes like that once i've stored them in a linked list...(can I?)
Kind regards
Craig

Answer 1

Your list nodes store an Item but that is only the base class. When you try to put a Manager or Staff in the list only the base class part of the object is copied into the list (this is called "slicing") and not the derived parts of the object.
When you call the virtual function you only get the base class overrider for the virtual, because the object stored in the list is only an Employee.
(You should consider making Node and List into templates, instead of doing #define Item Employee)