Thread: Linked List question...

To my knowledge, you can't do that. A linked list is a single struct or class, you can't use seperate ones unless they are part of the linked list struct. Search google.com for linked list tutorials for more information.

>>All of the classes need a first name, last name holder. Some need an employee ID #, some need a client ID number (alphanumeric), etc
Can you declare your struct like.

Code:

struct X{
     string firstname,lastname;
     union Y
     {int employeeID;
       int clientID;
      };
      struct X *next;
};

>>I'm trying to create a linked list using different types of nodes. Some nodes will have the same structure and some will have a different one (ie different # of value fields, different types of fields - int,string, char,etc.
You can have a void pointer in C structure.That can point to any structure.So I think you can use it.
I may be wrong

Putting all that information in a linked list is a bad idea, especially for big databases. I suggest getting the data you need only when you need it, one structure at a time, via serialization. Not only does this save memory for other important parts of your application but backups will always be there incase of a crash or if they want to see the last database they viewed. This isn't exactly what you are looking for, but an idea you could implement in the future when your program gets larger.

Unfortunately for link lists to work, you have to know your data type which I think you do but I think you are underestimating the power of linked lists. Any type of data can be put into them, classes, other structs, int, chars etc etc etc. you just have to know it, or use templates as chad suggested. Here's an example:

Code:

struct linkedlist
{
  MyFirstClass class1;
  MySecondClass class2;
  MyThirdClass class3;
  int number;
  char* string;
  // ...etc
  linkedlist* next;

  //Construction/Destruction
} linkedlist;

As you can see, any data you want can go in them. Choose wisely and good luck.

I think you could use templates. Here's an example:

Code:

template <typename T, T2> //syntax may not be correct
struct linkedlist
{
    T class1;
    T2 class 2;
    // Whatever else..
    linkedlist* next;
};

// And to call it:

linkedlist* list<MyClass1, MyClass2> = new linkedlist<MyClass1, MyClass2>;
//Again, may not be correct, its been awhile...

Virtual functions allow you to employ "polymorphism", which means when you use a base class pointer to call a function, the function that is called is not the function in the class corresponding to the pointer type, e.g. your base class. The function that is called is in the class corresponding to the object that the pointer points to, e.g. a derived class. So, each derived class can uniquely define the virtual function to do whatever it wants, like display all it's various member variables.

A virtual function is just a function with the same name in the base class and all the derived classes with the keyword "virtual" in front of it. "virtual" means you are requesting what is called "dynamic binding", which means when you have a base class pointer and call a function with the pointer, you want the function call to go to the object the pointer points to instead of the base class.

So, you need to do these steps:

1) Create a linked list of pointers to base class
2) Declare a virtual function in your base class
3) Declare a virtual function with the same name in each of your derived classes
4) Define the function in your derived classes to do whatever you want.
5) Create objects of your derived class and put them in your linked list
6) Retrieve one of the pointers from your linked list and call the function with it. The function that executes will the version of the function in the object that the pointer points to.