Reversing Linked List with Recursion, using STL - c++

Question

Code for Reversing Linked List with Recursion, using STL
#include<iostream>
#include<conio.h>
#include<list>
using namespace std;
template<typename T>
class node
{
public:
T data;
node<T> *next;
node(){ next = NULL; }
node(const T& item, node<T> *nextnode = NULL)
{
data = item;
next = nextnode;
}
};
template<typename T>
class Reverse_list
{
private:
node<T> *head;
void reverse(node<T> *front);
public:
Reverse_list(){ head = NULL; }
//template<typename T>
void Reverse();
template<typename T>
void Display( list<T>& alist );
};
int main()
{
Reverse_list <int> rl;
list<int> intlist;
int size, no;
cout << "Size of List ?? ";
cin >> size;
for (int i = 1; i <= size; i++)
{
cout << "Enter the " << i <<" "<< "element";
cin >> no;
intlist.push_front(no);
}
rl.Display(intlist);
rl.Reverse();
rl.Display(intlist);
_getch();
return 0;
}
template<typename T>
void Reverse_list<T>::Display(list<T>& alist)
{
list<int>::iterator iter = alist.begin();
while (iter != alist.end())
{
cout << *iter << " ";
iter++;
}
}
template<typename T>
void Reverse_list<T>::reverse(node<T> *front)
{
if (front->next == NULL)
{
head = front;
return;
}
reverse(front->next);
node<int> *back = front->next;
back->next = front;
front->next = NULL;
}
template<typename T>
void Reverse_list<T>::Reverse()
{
reverse(head);
}
The above code generates 2 errors.
Error 1) No instance of function template matches the argument list. ( No error number.)
If I remove line 1 ( mentioned in a code ) then above error is no more. ( Why? )
Error 2) C2783: 'void Reverse_list::Reverse1(void)' : could not deduce template argument for 'T'
How to solve above errors.
In above program , I wanted to pass " head" node ( which is private ) as
argument to Reverse function. But we can not access private member outside of the class. So I passed indirectly. Is this a correct way of passing ?? Or there is some other way of accessing private data ??

Answer 1

I'm not sure to understand your intentions but...
You're trying to declare a method (reverse()) inside another method (Reverse()) ? Uhmmm....
We return to this later.
Imagine that the following instruction is correct instruction of Reverse_list<T>::Reverse()
node<T> *back = front->next;
Why you declare back as a pointer to a generic Node<T> when you assign front->next (so a specific Node<int>) to it?
If you define back as a node<int> pointer, the method Reverse() has no longer reason to be a template (dependant from T) method. And you can avoid both errors.
With your actual code, when you call
rl.Reverse();
you call a template method but the compiler doesn't know how to determine the type T. You could explicit it in this way
rl.Reverse<int>();
but, as written before, I thik it's better if you remove the whole template part.
Or, alternatively, you can transform the whole class in a template class; where head is a pointer to a generic Node<T>, not a specifica Node<int>.
Something like (if I understand correctly your intentions)
template <typename T>
class Reverse_list
{
private:
node<T> *head;
void reverse (node<T> * front);
public:
Reverse_list() : head(NULL)
{ }
void Reverse();
void Display(list<T>& alist);
};
template<typename T>
void Reverse_list<T>::reverse (node<T> * front)
{
if (front->next == NULL)
{
head = front;
return;
}
reverse(front->next);
node<T> *back = front->next;
back->next = front;
front->next = NULL;
}
template<typename T>
void Reverse_list<T>::Reverse()
{ reverse(head); }
In this case, in main(), rl should be declared as
Reverse_list<int> rl;
fixing T as int, and the call to Reverse() should be
rl.Reverse();
--- EDIT 2016.05.10 ---
With the "template Reverse_list" solution, you should correct three points (at last).
1) in Reverse_list class declaration, you have commented the template<typename T> row before void Reverse(); good; you should delete (comment) the same line (for the same reason) before void Display( list<T>& alist );; so the class become
template<typename T>
class Reverse_list
{
private:
node<T> *head;
void reverse(node<T> *front);
public:
Reverse_list(){ head = NULL; }
//template<typename T>
void Reverse();
//template<typename T>
void Display( list<T>& alist );
};
2) Display() now is a method of a templated class; so the line
list<int>::iterator iter = alist.begin();
become
list<T>::iterator iter = alist.begin();
3) reverse() now is a method of a templated class; so the line
node<int> *back = front->next;
become
node<T> *back = front->next;