SPUG: C question ;)
benjamin at dzhan.com
Mon Mar 11 11:21:14 CST 2002
Yes, that's what I was essentially asking. I wanted to make sure that it
was normal array/pointer stuff and nothing special had to be done because
it was shared memory.
Thanks for your help!
On Sun, 10 Mar 2002, Scott Blachowicz wrote:
> On Sun, Mar 10, 2002 at 05:35:38PM -0800, Benjamin Franks wrote:
> > ...
> > int shmid=shmget((ftok("blah/blah",1), 1000*sizeof(my_struct), IPC_CREAT | 0666);
> > Then when I attach the shmid to a pointer, do I want to attach a pointer
> > of the my_struct type, as in:
> > my_struct *ptr;
> > ptr=shmat(shmid,NULL,0);
> > I guess that's where my confusion lies. Let's say I want to work on the
> > 500th element of my shared memory array of my_struct's. How can I do it?
> Well...in C, an array name is kind of like a constant ptr and array indexing
> is just a form of pointer arithmetic, so once you have a pointer, you're in
> /* Set all of the elements to the current time. */
> for (i = 0; i < 500; i++) ptr[i].a = ptr[i].b = time(NULL);
> /* All of these should be equivalent (unless I'm remembering wrong). */
> (ptr+499)->a = 0;
> (*(ptr+499)).a = 0;
> ptr.a = 0;
> 499[ptr].a = 0; /* !! */
> Is that what you wanted?
> Scott Blachowicz
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