OpenEuphoria

Re: Semaphore help

• Posted by jbrown105 at speedymail.org Jun 05, 2002
• 582 views

On  0, Bernie Ryan <xotron at localnet.com> wrote:
> 
> 
> jbrown105 at speedymail.org wrote:
> > I have tried to implement the code for semaphores, but it seems
> > not to be working. The main limitation is that fact that one of
> > the paramters of a function (semctl) has a union as its type.
> > How does one create/pass a union as a paramter to a C func?
> > (It would be nice to also have examples of using semaphores, but
> > I have the lpg (linux programmers guide) in addition to the
> > man pages, so if none can be provided, I can manage.)
> 
> All a union is is a storage location that can contain different
> size values. To use it all you need to do is know the largest
> value that will fit in the union and this will be the size that
> you will use when allocating the union size.
> Then you can store any value that is listed in the union values.
> in the same storage. The only thing you have to be careful
> to use the correct size for the value when poking it into the storage.
> I hope this makes sense.
> 
> Bernie
> 

It does. However I am unclear as how to define a C func which
uses a union.

       union semun {
               int val;                    /* value for SETVAL */
               struct semid_ds *buf;       /* buffer for IPC_STAT,
               IPC_SET */
               unsigned short int *array;  /* array for GETALL, SETALL
               */
               struct seminfo *__buf;      /* buffer for IPC_INFO */
       };

       int semctl (int  semid, int semnum, int cmd, union semun arg);

Thats the C prototype. How do I use define_c_func() to have a union
as a parameter? I got this far:

semctl_ = define_c_func(so, "semctl", {C_INT, C_INT, C_INT, }, C_INT)

How do I finish it?

TIA,
jbrown



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