Adding function templates to classes - c++

Question

So far, I have implemented a basic LinkedList. This works, but only for integers, and I would like it to work for any type.
I'm trying to get it to work for first any same type (i.e a LinkedList of just strings, or then just ints). After, I would like it to find a way of making it a LinkedList of anything (containing strings, then ints, then longs, all in one list).
#include <iostream>
struct Node{
Node(int value);
Node *next;
int data;
};
Node::Node(int value){
this->data = value;
this->next = nullptr;
}
struct LinkedList{
Node *head;
LinkedList();
void push_back(int value);
void print();
};
LinkedList::LinkedList(){
this->head = nullptr;
}
void LinkedList::push_back(int value){
Node *n = new Node(value);
if(this->head == nullptr){
this->head = n;
} else {
Node *cursor = this->head;
while (cursor->next != nullptr){
cursor = cursor->next;
}
cursor->next = n;
}
}
void LinkedList::print(){
Node *cursor = this->head;
while(cursor != nullptr){
std::cout << cursor->data << '\n';
cursor = cursor->next;
}
}
int main(){
LinkedList l = LinkedList();
l.push_back(1);
l.push_back(2);
l.print();
}
The above works, however, only for ints.
I'm knew, but I think the way is to use templates, however, doing so, I seem to be doing overkill? and it doesn't compile? Is there a cleaner was to do this?
#include <iostream>
template <typename T>
struct Node {
Node(T value);
int data;
Node<T> *next;
};
template <typename T>
Node<T>::Node(T value){
this->next = nullptr;
this->data = value;
}
template <typename T>
class LinkedList{
public:
LinkedList();
Node<T> *head;
void push_back(T data);
void print();
};
template <typename T>
LinkedList<T>::LinkedList(){
this->head = nullptr;
}
template <typename T>
void LinkedList<T>::push_back(T data){
Node *n = new Node(data);
if(this->head == nullptr){
this->head = n;
} else {
Node *cursor = this->head;
while(cursor->next != nullptr){
cursor = cursor->next;
}
cursor->next = n;
}
}
template <typename T>
void LinkedList<T>::print(){
Node *cursor = this->head;
while(cursor != nullptr){
std::cout << cursor->data << '\n';
cursor = cursor->next;
}
}
int main(){
LinkedList<T> *list = new LinkedList<T>();
list->push_back(1);
list->push_back(2);
list->push_back(3);
}

Answer 1

When declaring template classes, you use the "T" as a 'type placeholder' in the declaration and implementation (as you have done). However, when you want to actually use an object of the templated class, you replace the "T" with the actual type you want.
So, in your main (assuming you want an int type), you would have code like this:
int main(){
LinkedList<int> *list = new LinkedList<int>(); // THIS object uses "int" wherever "T" occurs in the declaration/implementation
list->push_back(1);
list->push_back(2);
list->push_back(3);
}
I also noticed a 'possible/probable error' in your struct declaration, where you specified that the data member is of (fixed) type int; maybe (almost certainly, actually, as you later assign a "T"-type value to it) you want this to vary according to the actual type requested? If so, make the following change:
template <typename T>
struct Node {
Node(T value);
// int data;
T data; // Data will be whatever "T" is when an object is created.
Node<T> *next;
};
Feel free to ask for further clarification and/or explanation.