c++ - Using a custom class with a custom template container

I'm trying to define a custom template container, and then add custom class objects (Students) into it. Here's my code:

class Student{
public:
    string subject;
    Student(string _subject){
        subject = _subject;
    }
};

And here's my LinkedList template code

template 
class LinkedList{

private:
    struct Node{
        Node *next;
        T value;

    };
    Node *root;
    Node *curr;
    int count;

public:
    LinkedList() : count(0), root(NULL){}
    void add(T val){
        if (root == NULL){
            root = new Node;

            root->value = val;
            root->next = NULL;
            curr = root;
        }
        else{
            curr->next = new Node;
            curr = curr->next;
            curr->value = val;
            curr->next = NULL;
        }

        count++;
    }

    void print(){
        for (Node *itr=root; itr != NULL; itr = itr->next){
            cout << itr->value << endl;
        }
    }
};


int main(){
    LinkedList a;
    Student sam("Math");
    a.add(sam)
}

When I run it, I get

linkedlist.cpp: In constructor ‘LinkedList::Node::Node()’:
linkedlist.cpp:27: instantiated from ‘void LinkedList::add(T) [with T = Student]’

linkedlist.cpp:133: instantiated from here

linkedlist.cpp:27: error: no matching function for call to ‘Student::Student()’
linkedlist.cpp:18: note: candidates are: Student::Student(std::string)

linkedlist.cpp:15: note: Student::Student(const Student&)
linkedlist.cpp: In member function ‘void LinkedList::add(T) [with T = Student]’:

linkedlist.cpp:40: note: synthesized method ‘LinkedList::Node::Node()’ first required here

I have no clue what that error really means, and what it's asking me to do. If I do this instead:

int main(){
    LinkedList a;
    Student sam("Math");
    a.add(&sam);

}

It works just fine.

But storing references to objects is not what I'm after. How can I get my LinkedList to make copies of the object I wish to add to it?

Thanks in advance!

Answer

First of all...

#include 

Now, change this...

struct Node {
    Node* next;
    T     value;
};

For...

struct Node {
    Node* next;
    T     value;

    inline Node(const T &value) : value(value), next(nullptr) {}
    inline Node(T &&value) : value(std::move(value)), next(nullptr) {}

};

And, this...

void add(T val) {
    if(this->root == nullptr) {
        this->root = new Node;
        this->root->value = val;
        root->next = NULL;

        curr = root;
    } else {
        curr->next = new Node;
        curr = curr->next;
        curr->value = val;
        curr->next = NULL;
    }

    count++;
}

For this...

void add(const T &val){
    if(this->root == nullptr) {
        this->root = new Node(val);
        this->curr = root;
    } else {
        this->curr->next = new Node(val);

        this->curr = this->curr->next;
    }

    this->count++;
}

void add(T &&val){
    if(this->root == nullptr) {
        this->root = new Node(std::move(val));
        this->curr = root;

    } else {
        this->curr->next = new Node(std::move(val));
        this->curr = this->curr->next;
    }

    this->count++;
}

What happens is that you're creating a Node object with new Node with it's implicit default constructor. That implies that the default constructor for Node::value is called. Then, can you tell me if there's any? No. Student does not have a default constructor, so this won't work.

BTW, I made some minor redesigns to your code, so to avoid several issues that appeared by the way. As a bonus, you can now use move semantics (try list.add(Student("Joe")))!

Also, remember to initialize curr to nullptr in the constructor initialization list!