functions that manipulate void pointers Post: 302378647

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Top Forums Programming functions that manipulate void pointers Post 302378647 by DreamWarrior on Tuesday 8th of December 2009 11:24:30 AM

12-08-2009

Registered User

You could go the way you're going with function pointers, but you may want to make the function prototype take two void * as arguments. While it isn't exactly type safe, it does allow you to call the function pointer without warnings regarding the types passed. If you don't do this, all your callers will need to know which of the two functions they are calling to pass the correct type safe parameters.

so something like:

Code:

struct server_t
{
     sockaddr_in * sin;
     server_t * next_;
}

struct player_t
{
     char name[10];
     player_t * next_;
}

typedef void (*add_entity_t)(void **list, void * target);

static void add_server_entity(void **_list, void *_new)
{
     #define list   ((struct server_t *) _list)
     #define new    ((struct server_t *) _new)

     new->next_ = *list;
     *list = new;

     #undef list
     #undef new
}


static void add_player_entity(void **_list, void *_new)
{
     #define list   ((struct player_t *) _list)
     #define new    ((struct player_t *) _new)

     new->next_ = *list;
     *list = new;

     #undef list
     #undef new
}

int main(int argc, char **argv)
{
     add_entity_t    entityFn;

     ....

    entityFn = add_server_entity;

    entityFn(&serverHead, newServer);
}

I fixed the "list" argument, which needs to be a pointer to pointer since you are changing its value and the caller needs to see the new value for everything to work.

However, to be honest, I think all this is just a "waste" of time. You should concentrate on making a list package that is generic. Like, add_entity just takes a list and a void * for the data. It allocates nodes appropriately and you allocate the data you want to add to the list outside and pass it to an "add to list" function. The list entity just stores the next/prev pointers and a void * for the data item. In C++ you could use templates, in C you have to sacrifice type safety for the generic data item.

DreamWarrior

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LEARN ABOUT OPENSOLARIS

remque

insque(3C)						   Standard C Library Functions 						insque(3C)

NAME

       insque, remque - insert/remove element from a queue

SYNOPSIS

       include <search.h>

       void insque(struct qelem *elem, struct qelem *pred);

       void remque(struct qelem *elem);

DESCRIPTION

       The  insque()  and remque() functions manipulate queues built from doubly linked lists.	Each element in the queue must be in the following
       form:

	 struct qelem {
		 struct qelem	*q_forw;
		 struct qelem	*q_back;
		 char		q_data[];
	 };

       The insque() function inserts elem in a queue immediately after pred.  The remque() function removes an entry elem from a queue.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Unsafe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       attributes(5), standards(5)

SunOS 5.11							    24 Jul 2002 							insque(3C)