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From: leather@osiris.cso.uiuc.edu
Newsgroups: comp.lang.c
Subject: Re: Need help with structure pointers
Message-ID: <8900002@osiris.cso.uiuc.edu>
Date: Tue, 13-Oct-87 02:07:00 EDT
Article-I.D.: osiris.8900002
Posted: Tue Oct 13 02:07:00 1987
Date-Received: Fri, 16-Oct-87 01:12:41 EDT
References: <1778@killer.UUCP>
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Nf-From: osiris.cso.uiuc.edu!leather    Oct 13 01:07:00 1987


> /* Written 11:39 pm  Oct  9, 1987 by tad@killer.UUCP 
> /* ---------- "Need help with structure pointers" ---------- */
> I've never bothered to get a complete grasp over structures before, and
> now it is hurting me.  Could someone please tell me the proper way to
> accomplish the following ugliness?
> 
> pgrogram deleted for ugliness ... |-)
>

      A very important distinction to remember is the difference between:
        - the structure member  operator "." and
        - the structure pointer operator "->"

      The member operator works with the name of a structure:
          x.s = 'X';

      The pointer operator works with the pointer to a structure:
          sp->s = 'X';

      You must also be very careful of how you de-reference your pointers
      (ie. how you access the data for which you have the pointer).
          *++(stuff->s) = 'X';

      Personally, I try not to mix the two operations; but, to each his own.
      "The C Programming Language" by Brian W. Kernighan & Dennis M. Ritchie
      treats the subject in depth.  Get a copy and read it (Chapter 6).



UNTIL THEN -
   TRY THIS:  (I only made it work; making it aesthetically pleasing is a 
               matter of taste &/or programming style, which I choose not
               to dig into here)

struct X {char *s;
          int   a, b;
         };
 
main()
{struct X x;
 struct X *sp;
 char   max[25];
 
 sp    = &x;
 sp->s = max;
 strcpy(x.s, "Some Stuff");
 fun(&x);
}
 
fun(stuff)
struct X *stuff;
{
 *++(stuff->s) = 'X';
 printf("%s\n", stuff->s); /* I want this to print "Xme Stuff" */
}

			Good Luck - Dave L.