Linked list containig different derived class objects in c++ - c++

Question

How we can create a linked list which can contain a different class of object. for example, if a person is base class and it has student and teacher as a derived class so How I can create a linked list which can contain both classes of objects like student also and teacher also.
below I wrote the source code for that but it is not working.
#include<iostream>
#include<string>
using namespace std;
int classNum;
class person
{
public:
string name;
public:
person(string="");
void show_p_name();
};
class student:public person
{
public:
string s_name;
int rollnum;
public:
student(string="", string="", int=100);
void show_name();
};
class worker:public person
{
public:
string w_name;
int work_id;
public:
worker(string="", string="", int=200);
void show_name();
};
// person
person::person(string nm)
{
name = nm;
}
void person::show_p_name()
{
cout << "In person class name is: " << name << endl;
}
// student inheriate person
student::student(string nm, string snm, int rolln)
:person(nm)
{
s_name = snm;
rollnum = rolln;
}
void student::show_name()
{
cout << "In student class name is: " << s_name << endl;
}
// worker inheriate person
worker::worker(string nm, string wnm, int wid)
:person(nm)
{
w_name = wnm;
work_id = wid;
}
void worker::show_name()
{
cout << "In worker class name is: " << w_name << endl;
}
// structure declaration
struct Node
{
person *p;
struct Node *next;
};
struct Node* createNode()
{
struct Node *t;
t = new struct Node;
classNum++;
if(t == NULL)
{
cout << "Memory Not Allocated\n";
//exit(0);
}
else
{
return t;
}
}
void initLink(struct Node *n)
{
n->next = NULL; //Make next as NULL
}
void initNode(struct Node *temp)
{
if((classNum % 2) == 0)
{
/*
temp->p = new student;
static_cast<student*>(temp->p)->name = "person_s_sahil";
static_cast<student*>(temp->p)->s_name = "student_sahil";
static_cast<student*>(temp->p)->rollnum = 100;
temp->p = static_cast<student*>(temp->p);
*/
temp->p = new student();
temp->p->name = "person_s_sahil";
temp->p->s_name = "student_sahil";
temp->p->rollnum = 100;
}
else
{
/*
temp->p = new worker;
static_cast<worker*>(temp->p)->name = "person_w_sahil";
static_cast<worker*>(temp->p)->w_name = "worker_sahil";
static_cast<worker*>(temp->p)->work_id = 100;
temp->p = static_cast<worker*>(temp->p);
*/
temp->p = new worker()
temp->p->name = "person_w_sahil";
temp->p->w_name = "worker_sahil";
temp->p->work_id = 100;
}
}
void attachEnd(struct Node **hptr, struct Node *tn)
{
struct Node *cn;
if(*hptr == NULL) //if list is empty
{
*hptr = tn; //attach new node to head
}
else
{
cn = *hptr; //get first node call as currunt node
while(cn->next != NULL) //get last node
{
cn = cn->next;
}
cn->next = tn; //attach new node to next of last node
}
}
void traverse(struct Node *hptr)
{
struct Node *temp;
if(hptr == NULL)
{
cout << "List is empty\n";
}
else
{
temp = hptr;
while(temp != NULL)
{
temp->p->show_name();
temp = temp -> next;
}
}
}
main()
{
struct Node *head = NULL;
struct Node *temp;
temp = createNode();
initLink(temp);
initNode(temp);
attachEnd(&head, temp);
traverse(head);
// like that I want to create node and attach to linked list
}

Answer 1

Proper approach would be to create linked list of pointers to objects of type Person.
Then you will populate it with pointers to instances of classes Student and Teacher. You have to create it dynamically (new keyword)
And now magic comes with using of keyword virtual for method declaration in Person class. Check this in google c++ polymorphism and C++ virtual method
If you latter call virtual method on pointer to Person object it will call proper method from derived class.
Do not forget to call delete for each element in list at the end of usage (program). And for this you have to define virtual destructor in Person class
In your case you should define Person class like this
class person
{
public:
string name;
virtual ~person() {};
public:
person(string="");
virtual void show_name();
};
Or another approach could be to use dynamic_cast<>() but for this you need to enable it in compiler. It is called RTTI (runtime type information). With dynamic cast you can safely cast from Person to Student or Teacher. If dynamic cast is not able to do cast it will return nullptr. So you can check this value.

Answer 2

Slightly fixed code (for purpose of compile-ability):
void initNode(struct Node *temp)
{
if ((classNum % 2) == 0)
{
/*
temp->p = new student;
static_cast<student*>(temp->p)->name = "person_s_sahil";
static_cast<student*>(temp->p)->s_name = "student_sahil";
static_cast<student*>(temp->p)->rollnum = 100;
temp->p = static_cast<student*>(temp->p);
*/
auto s = new student();
temp->p = s;
temp->p->name = "person_s_sahil";
s->s_name = "student_sahil";
s->rollnum = 100;
}
else
{
/*
temp->p = new worker;
static_cast<worker*>(temp->p)->name = "person_w_sahil";
static_cast<worker*>(temp->p)->w_name = "worker_sahil";
static_cast<worker*>(temp->p)->work_id = 100;
temp->p = static_cast<worker*>(temp->p);
*/
auto p = new worker();
temp->p = p;
temp->p->name = "person_w_sahil";
p->w_name = "worker_sahil";
p->work_id = 100;
}
void traverse(struct Node *hptr)
{
struct Node *temp;
if (hptr == NULL)
{
cout << "List is empty\n";
}
else
{
temp = hptr;
while (temp != NULL)
{
temp->p->show_p_name();
temp = temp->next;
}
}
}
If you fix your code, it will work (at a glance).