C++ - Reverse function in a template class stack implementation - c++

Question

this is my stack implementation using template with a struct type node and a class type stack:
Stack.h
#ifndef STACK_H_
#define STACK_H_
#include <cstdlib>
#include <iostream>
#include <cassert>
using namespace std;
template <class t>
struct node{
t data;
node<t>* next;
};
template <class t>
class stack
{
public:
stack();
~stack();
bool isEmpty(){ return (top_ptr=NULL);};
void push(const t&);
void pop();
t top() const;
void reverse();
void clear();
void print();
private:
node<t>* top_ptr;
};
template <class t>
stack<t>::stack()
{
top_ptr=NULL;
}
template <class t>
stack<t>::~stack()
{
while(top_ptr != NULL) pop();
}
template <class t>
void stack<t>::push(const t& source)
{
node<t>* new_node = new node<t>;
new_node->data = source;
new_node->next = top_ptr;
top_ptr = new_node;
cout << "Inserito!" << endl;
}
template <class t>
void stack<t>::pop()
{
node<t>* remove = top_ptr;
top_ptr = top_ptr->next;
delete remove;
cout << "Rimosso!" << endl;
}
template <class t>
t stack<t>::top() const
{
assert(top_ptr != NULL);
return top_ptr->data;
}
template <class t>
void stack<t>::clear()
{
node<t>* temp;
while(top_ptr != NULL)
{
temp = top_ptr;
top_ptr = top_ptr->next;
delete temp;
}
cout << "Clear completato!" << endl;
}
template <class t>
void stack<t>::reverse()
{
stack<t> new_stack;
while(top_ptr != NULL)
{
new_stack.push(top_ptr->data);
pop();
}
cout << "Reverse completato!" << endl;
}
template <class t>
void stack<t>::print()
{
node<t>* ptr = top_ptr;
while(ptr!=NULL)
{
cout << " " << ptr->data << endl;
ptr = ptr->next;
}
}
#endif /* STACK_H_ */
And this is the main.cpp:
#include "stack.h"
int main()
{
stack<int> stackino;
for(int i = 0; i<10; i++) stackino.push(i);
stackino.pop();
cout << "top(): " << stackino.top() << endl;
stackino.print();
cout << "Invoco clear()" << endl;
stackino.clear();
cout << "Stackino dopo clear():" << endl;
stackino.print();
cout << "Invoco reverse()" << endl;
stackino.reverse();
cout << "Stackino dopo reverse()" << endl;
stackino.print();
cout << "FINE!" << endl;
return 0;
}
The problem is reverse() that causes a crash of the program, I guess "top_ptr = new_stack.top_ptr" is wrong but it makes compile and execute, but crashes. Can someone help me correct this?

Answer 1

I think I understand the issue. Let me know if I am interpreting this wrong.
When you do top_ptr = new_stack.top_ptr, you're putting the temporary stack's top as yours.
The problem is, when that temporary stack gets destructed, it still has the same top_ptr, and deletes all the memory that was associated with it. That leaves your real stack with a bad top_ptr.
I would suggest trying:
top_ptr = new_stack.top_ptr;
new_stack.top_ptr = NULL;
So that it doesn't clear away your stack, and leave you with a bad pointer.
Hope that works?