Singly linked list using template with a struct as elements in C++;

Question

I'm trying to create a linked list to store student's informations, with Student is a struct like this:

struct Student
{
    int id;
    string name;
    //etc
};

I have two templates for node and list with a basic function:

template <class T>
struct Node {
    T data;
    Node <T> *pNext;
    Node () : pNext(NULL) {}
    Node (T &a) : data(a), pNext(NULL) {}
};

template <class T>
class LinkedList
{
    Node <T> *Head;
    size_t lSize;
public:
    LinkedList(): Head(NULL), lSize(0) {}
    ~LinkedList();

    void linsert(T& a);
};

With linsert() to insert new node at the beginning of the list:

template <class T>
void LinkedList<T>::linsert(T& a)
{
    if (Head==nullptr)
        Head=a;
    else
    {
        a->pNext=Head;
        Head=a;
    }
    lSize++;
}

To the testing: I've tried creating new nodes and linking them manually (without using the linked list) and everything seems to work fine:

Node <Student> *s1 = new Node <Student>;
s1->data.id=1;
s1->data.name="Anna";

Node <Student> *s2 = new Node <Student>;
s2->data.id=2;
s2->data.name="Bob";
s1->pNext=s2;

Node <Student> *s3 = new Node <Student>;
s3->data.id=3;
s3->data.name="James";
s2->pNext=s3;

Here's the problem: I tried creating a new linked list, and use the linsert() to add new students to the list with a simple for loop:

LinkedList <Node<Student>> *l=new LinkedList <Node<Student>>;

for (int=0; i<10; i++)
{
    Node <Student> *s = new Node <Student>;
    s->data.id=i;
    s->data.name="Name";

    l->linsert(s);
}

When compile, I get this error message points to the line

l->linsert(s);

error: no matching function for call to 'LinkedList<Node<Student> >::linsert(Node<Student>*&)'
note: candicate: void LinkedList<T>::linsert(T&) [With T=Node<Student>]
note: no known conversion from argument 1 from 'Node<Student>*' to 'Node<Student>&'

I always have problem using pointer and reference so after a good hour not figuring anything out I gave up. Please help me to solve this.

I'm using CodeBlock and if there's any improvement I can make for the above codes, it would be appreciated if you could tell me.

`LinkedList ` Note how the `T` is applied to the `Node` members of `LinkedList` — user4581301, Sep 20 '19 at 05:23
Unrelated: `LinkedList *l=new LinkedList ;` could be (and probably should be) `LinkedList l;` [Avoid `new`ing stuff unless forced to.](https://stackoverflow.com/questions/6500313/why-should-c-programmers-minimize-use-of-new) — user4581301, Sep 20 '19 at 05:25

Remy Lebeau · Accepted Answer · 2019-09-20T05:30:24.693

Your linsert() is implemented incorrectly. It should take a Student as input and create a new node for it. You are trying to create nodes outside of linsert() and pass them in, which is not the right way to use linked list classes. The node management should be kept inside the class.

Try this instead:

template <class T>
void LinkedList<T>::linsert(T& a)
{
    Node<T> *n = new Node<T>(a);
    n->pNext = Head;
    Head = n;
    ++lSize;
}

LinkedList<Student> l;

for (int i = 0; i < 10; i++)
{
    Student s;
    s.id = i;
    s.name = "Name";
    l.linsert(s);
}

Singly linked list using template with a struct as elements in C++;

1 Answers1