Dfyjkt

How to define a list which can hold different types of objects in c++, just like python list? I tried the following code

#include <iostream>

template< typename t >
struct Node 
 t val;
 Node *next;
;

int main() 
 Node<int> a;
 a.val = 1;
 Node<char> b;
 b.val = 'b';
 a.next = &b;
 b.next = NULL;

But compiler gives the following error:

main.cpp:14:15: error: cannot convert 'Node<char>*' to 'Node<int>*' in 
assignment
 a.next = &b;
 ^

There is a couple problems with this code, first of which is the next member of Node does not have a template type defined, usually in this case if you want to make a linked list of one generic type you would do something like Node<t>* next. Second is the fact that you are assigning what seems to be an Node* to a Node*.

If what you are trying to do is create a linked list of different types you cannot do it this way. Simply put, the reason is because you have to pass in a type for the t argument and because of this each node must have a defined type. The purpose of template classes is not to allow user to allocate any generic type willy nilly but rather to simplify repeated implementation of a class by allowing you to pass in a type as a parameter. As an example: a List<int> vs a List<char> simplyfies you from having to make a IntList class and a CharList class.

If you want the behavior of storing any dynamically allocated types within the same array then this is not as easy. I would recommend looking at c++17 std::any and std::variant types or if older version of the language the boost boost::any and boost::variant types from the boost library. Other ways to do this without the standard libraries is by using polymorphism or void*.