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Passing type as a parameter; generalised linked list in C?

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Passing type as a parameter; generalised linked list in C?

May 14th, 2008

I was trying to revise my linked list and implement it in C to check if there is a difference in performance... just as a sort of weird hobby..

In the absence of templates I'm trying to figure out how to pass a type as a parameter for this purpose. For example va_arg(arg, int) retrieves an int. I know it's a macro, not a function, but I still can't figure out how this is done.. if I could add this kind of functionality and then store the type somewhere in some variable then I could probably implement the linked list using void pointers.

Alternatively, would it be possible to just use void pointers and sizeof? How would one ensure that the user doesn't start mixing types within the linked list then?

Thanks for any advice, I'm really bored..

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Re: Passing type as a parameter; generalised linked list in C?

May 14th, 2008

va_args will be of no help to you because all it does is point to the beginning byte of the stack where a variable of unknown size starts. The program still has to know the data type.

This is how I impleneted a general-purpose linked list

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
typesed struct node
{
    void * data; // data for this node
    struct node* next;
    struct node* prev;
} LINK;
typesed struct node
{
    void * data; // data for this node
    struct node* next;
    struct node* prev;
} LINK;

To insert a node at the head of the linked list.

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
struct node* insertHead(LINK** head, void* data)
{
      LINK* newNode = malloc(sizeof(LINK));
      newNode->data = data;
      newNode->next = NULL;
      newNode->prev = NULL;
      if( *head == NULL)
           *head = newNode;
     else
     {
         newNode->next = *head;
         *head = newNode;
     }
}
struct node* insertHead(LINK** head, void* data)
{
      LINK* newNode = malloc(sizeof(LINK));
      newNode->data = data;
      newNode->next = NULL;
      newNode->prev = NULL;
      if( *head == NULL)
           *head = newNode;
     else
     {
         newNode->next = *head;
         *head = newNode;
     }
}

Don't PM me with questions -- you might get a nasty PM in response. If you have a question then post it in one of the forums.

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Re: Passing type as a parameter; generalised linked list in C?

May 15th, 2008

I think the node structure should be like this:

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 C Syntax (Toggle Plain Text) 
struct node {
    void *data;
    int type;
    struct node *next;
    struct node *prev;
 
}LINK;
struct node {
    void *data;
    int type;
    struct node *next;
    struct node *prev;

}LINK;

where: type is used for type. For example type=1 indicates int, type=2 indicates float, type=3 indicates userdefine and so on...

and Insert function will look like this:

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
int inser(LINK **head, void data, int type) {
   if(type==1) { // int
      LINK *newnode = (LINK*)malloc(sizeof(LINK));
      newnode->data = malloc(sizeof(int));
 
   }
 
and so on......
 
 
 
}
int inser(LINK **head, void data, int type) {
   if(type==1) { // int
      LINK *newnode = (LINK*)malloc(sizeof(LINK));
      newnode->data = malloc(sizeof(int));

   }

and so on......



}

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