Implementing a linked list in C

[Javasnob]

Hey guys, I'm new to C, and to test/hone my skills, I decided to try to implement a linked list. My only question is...

How do you make it so you can use different data types in a linked list? Is this possible in C, or do you have to compile seperate versions for each type?

Thanks in advance!

[Workaphobia]

C++'s solution is templates. With C, you have to use the type-unsafe method of casting to void pointers. I don't know much more beyond that.

[CodeRoot]

How do you make it so you can use different data types in a linked list?

Look up and read about "structures" (keyword 'struct')...

[Roxoff]

How do you make it so you can use different data types in a linked list?

Look up and read about "structures" (keyword 'struct')...

Close, the C method is to use a union:

typedef union test
{
   unsigned char* name;
   unsigned long  identifier;
   struct age
   {
      char years;
      char months;
      char days;
      char hours;
   };
} test_t;

Then stick that into your linked list type:

typedef struct linked_list
{
   test_t * item;
   struct linked_list* next;
} linked_list_t;

linked_list_t* list = NULL;

From C++ there are more options. Templates classes can be used, or just a simple base class from which all data entries in the list are derived. You can even implement your whole list using a class if you feel like that, and it can store polymorphic types or other classes or whatever you like.

[CodeRoot]

How do you make it so you can use different data types in a linked list?

Look up and read about "structures" (keyword 'struct')...

Close, the C method is to use a union:

typedef union test
{
   unsigned char* name;
   unsigned long  identifier;
   struct age
   {
      char years;
      char months;
      char days;
      char hours;
   };
} test_t;

Then stick that into your linked list type:

typedef struct linked_list
{
   test_t * item;
   struct linked_list* next;
} linked_list_t;

linked_list_t* list = NULL;

From C++ there are more options. Templates classes can be used, or just a simple base class from which all data entries in the list are derived. You can even implement your whole list using a class if you feel like that, and it can store polymorphic types or other classes or whatever you like.

Roxoff:
No, not close - exact.

The purpose of unions is to allow variables of different data types to occupy the same data space. I do not believe that is what Javasnob is asking for or needing in this particular example. (By the way, you should re-think your union... :P )

Javasnob:
I believe Roxoff may have mis-read your question... And, after re-reading your question a few more times, I believe I may have mis-read it also... Did you mean that you wanted to link a collection of data variables (each link) of different data types (what I thought you meant) - or did you mean you wanted to link a single data variable (each link) - but with "interchangeable" data types (i.e., next "run" - different data type)? Or, please re-state the question...

In any case, you'll end up using structures. This is a more correct example:

struct linked_data
{
  <structure elements>  // variable declarations
  .
  .
  struct linked_data *next;  // link to next
  struct linked_data *prev;  // link to previous, if a doubly-linked list
&#125; linked_list;  // create first list element

struct linked_data *list_pointer = &linked_list;

The typedefs are O.K., but not really needed in this example.



So, then...

Look up and read about "structures" (keyword 'struct')...