Question

I’ve written a template Link list, but when I try to add an object to it I get the error “C2512 ‘Customer’: No Appropriate default constructor available” thrown from the node constructor.

Code:

#pragma once
#include <iostream>
using namespace std;

template <class T>
class node;

template <class T>
class l_list
{

public:
    l_list() { head = tail = NULL; }
    ~l_list();
    void add(T &obj);
    T remove(int ID);
    void print(ostream &out);

private:
    node<T> *head, *tail;
};

template <class T>
class node
{
public:
    template<class> friend class l_list;
    node() {next = NULL;}
private:
    T data;
    node *next;
};

template <class T>
l_list<T>::~l_list()
{
}

template <class T>
void l_list<T>::add(T &obj)
{
    node<T> *ptr = new node<T>;
    ptr -> data = obj;
    ptr -> next = head;
    head = ptr;

    if (tail == NULL) {tail = ptr;}
}

template <class T>
T l_list<T>::remove(int ID)
{
    int i = 0;
    node<T> * ptr = head;

    while (ptr -> data -> id != ID)
    {
        ptr = ptr -> next;
    }
}

template <class T>
void l_list<T>::print(ostream &out)
{
    int i = 0;
    node<T> *ptr = head;
    while ( ptr != NULL )
    {
        out << ptr -> data << endl;
        ptr = ptr -> next;
        i++;
    }
}

and the object that I try and put in the list

l_list<Customer> customers;
Customer bob("Bob", "25 Bob Lane", "01bob82", "M", "bob/bob/bob");
customers.add(bob);

edit to add Customer:

#pragma once
#include "l_list.h"
#include "Account.h"
#include <string>

using namespace std;

class Customer
{
private:
    l_list<Account> accounts;
    string name;
    string address;
    string telNo;
    string sex;
    string dob;

public:
    Customer(string name, string address, string telNo, string sex, string dob)
    {
        Customer::name = name;
        Customer::address = address;
        Customer::telNo = telNo;
        Customer::sex = sex;
        Customer::dob = dob;
    }

    void createAccount()
    {
        cout << "What type of account?";

    }

    ~Customer()
    {
    }
};

Answer 1

This line:

node<T> *ptr = new node<T>

Is trying to default-construct a T within node. Since there is no default constructor, no compiley =P

You can address this by using the copy constructor (which you define or use the default one , so long as T properly complies with The Rule of Three) or by defining a default constructor for T. I prefer the former if I want to harden construct access to T

node<T> *ptr = new node<T>(obj);

Of course, you need to define a proper constructor for node<T>::node(const T&)

class node
{
public:
    template<class> friend class l_list;

    // T-copy-ctor-based constructor
    node(const T& obj) : data(obj), next(NULL) {};

private:
    T data;
    node *next;
};

Been a slow morning so sorry if I messed something up in there. =P