Question about a stack using array of pointers
Well, I had an assignment for class to convert an array of objects stack to an array of pointers stack. I think that I've oversimplified the assignment, because the program compiles okay, but whenever I push an item onto the stack, the program crashes. Using debug, it looks like it was assigning a value of 5 to my pointer, which is the max # of items in my array. I can't figure out why this is. Also, this is a class, which I'm not exactly comfortable with yet.
Scroll to the bottom if you want to see the actual problem without the long explanation. Sorry for the backwards post. :o
This is my class:
Code:
#ifndef STACKTYPE_H
#define STACKTYPE_H
#include "ItemType.h"
// The user of this file must provide a file "ItemType.h" that defines:
// ItemType : the class definition of the objects on the stack.
// MAX_ITEMS: the maximum number of items on the stack.
// Class specification for Stack ADT in file Stack1.h
class FullStack
// Exception class thrown by Push when stack is full.
{};
class EmptyStack
// Exception class thrown by Pop and Top when stack is emtpy.
{};
class StackType
{
public:
StackType(int); // added 10/9/2003
StackType();
// Class constructor.
bool IsFull() const;
// Function: Determines whether the stack is full.
// Pre: Stack has been initialized.
// Post: Function value = (stack is full)
bool IsEmpty() const;
// Function: Determines whether the stack is empty.
// Pre: Stack has been initialized.
// Post: Function value = (stack is empty)
void Push( const ItemType & item);
// Function: Adds newItem to the top of the stack.
// Pre: Stack has been initialized.
// Post: If (stack is full), FullStack exception is thrown;
// otherwise, newItem is at the top of the stack.
void Pop();
// Function: Removes top item from the stack.
// Pre: Stack has been initialized.
// Post: If (stack is empty), EmptyStack exception is thrown;
// otherwise, top element has been removed from stack.
ItemType Top();
// Function: Returns a copy of top item on the stack.
// Pre: Stack has been initialized.
// Post: If (stack is empty), EmptyStack exception is thrown;
// otherwise, top element has been removed from stack.
private:
int top;
ItemType ** items; // changed 10/9/2003
};
#endif
That part is fine I think.
This is ItemType if you're curious:
Code:
// ItemType.h StackDriver
#ifndef ITEMTYPE_H
#define ITEMTYPE_H
const int MAX_ITEMS = 5;
typedef int ItemType;
#endif
This is my driver program:
Code:
// Test driver
#include <iostream>
#include <fstream>
#include "StackType.h"
using namespace std;
bool copyStack( StackType & d, StackType & s)
{
StackType temp;
while ( !s.IsEmpty() )
{
temp.Push( s.Top() );
s.Pop();
}
return true;
}
int main()
{
StackType s;
ItemType work;
while ( ! s.IsFull())
{
cin >> work;
s.Push(work);
}
// empty the stack - printing the data
while ( !s.IsEmpty() )
{
work = s.Top();
cout << work;
s.Pop();
}
return 0;
}
I believe that is fine as well. I don't think it should have to change?
Finally, this is my stack:
Code:
/ File: StackType.cpp
#include "StackType.h"
#include <iostream>
ItemType dummy;
StackType::StackType()
{
top = -1;
}
bool StackType::IsEmpty() const
{
return (top == -1);
}
bool StackType::IsFull() const
{
return (top == MAX_ITEMS-1);
}
void StackType::Push(const ItemType & newItem)
{
if( IsFull() )
throw FullStack();
top++;
*items[top] = newItem;
}
void StackType::Pop()
{
if( IsEmpty() )
throw EmptyStack();
*items[top] = dummy;
top--;
}
ItemType StackType::Top()
{
if (IsEmpty())
throw EmptyStack();
return *items[top];
}
I'm quite sure this is where my problem lies. I think that I can't just do this:
*items[top] = newItem;
as that seems to be where the problem occurs. How would you go about pushing the value onto the stack? I don't really understand how pointers change this.
Also, sorry for posting so much code. But last time I didn't post enough, so I thought I would avoid that problem this time.
