From:	"Damian Yerrick" <web DOT poison AT pineight DOT 8m DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: HELP ! (returning structures)
Date:	Wed, 29 Sep 1999 16:56:30 -0500
Organization:	Rose-Hulman Institute of Technology
Lines:	68
Message-ID:	<7su21s$9rk$1@solomon.cs.rose-hulman.edu>
References:	<7srkeu$3kh$1 AT tron DOT sci DOT fi> <37f173b9 DOT 2534667 AT newsserver DOT cc DOT monash DOT edu DOT au>
NNTP-Posting-Host:	yerricde.laptop.rose-hulman.edu
X-Trace:	solomon.cs.rose-hulman.edu 938642300 10100 137.112.205.146 (29 Sep 1999 21:58:20 GMT)
X-Complaints-To:	news AT cs DOT rose-hulman DOT edu
NNTP-Posting-Date:	29 Sep 1999 21:58:20 GMT
X-Priority:	3
X-MSMail-Priority:	Normal
X-Newsreader:	Microsoft Outlook Express 5.00.2314.1300
X-MimeOLE:	Produced By Microsoft MimeOLE V5.00.2314.1300
To:	djgpp AT delorie DOT com
DJ-Gateway:	from newsgroup comp.os.msdos.djgpp
Reply-To:	djgpp AT delorie DOT com

> On Wed, 29 Sep 1999 02:57:07 +0300, "stefan fröberg"
> <traveler AT netti DOT fi> wrote:
>
> >How can functions return whole structures ?
> >
> >Example:
> >
> >struct    DATE
> >{
> >    unsigned char    day_of_week;
> >    unsigned short    year;
> >    unsigned char    month;
> >    unsigned char    day;
> >}
> >
> >extern    struct DATE    GetDate(void);
> >
> >int    main(void)
> >{
> >    struct   DATE    today;
> >    today = GetDate();
> >    printf("%u\n",today.day_of_week);
> >    printf("%U\n",today.year);
> >    printf("%u\n",today.month);
> >    printf("%u\n",today.day);
> >}

Davin responded:

> struct DATE GetDate(void)
> {
>   struct DATE x;
>   x.day_of_week = GetDayOfWeek();
>   x.year = ...
>   ....
>   return x;
> }


Davin, your solution is IMHO not the best. Passing structures
on the stack is inefficient. The best way to return a structure is
to fill in a blank structure pointed to in the arguments.

void GetDate(struct DATE *the_date)
{
  x->day_of_week = GetDayOfWeek();
  x->year = ...
  ....
}

int main(void)
{
  struct DATE today;

  GetDate(&today);
  printf("%u\n",today.day_of_week);
  printf("%U\n",today.year);
  printf("%u\n",today.month);
  printf("%u\n",today.day);
}

Davin, I challenge you to find one C library function that returns
a struct on the stack. :-)

Damian Yerrick
http://pineight.webjump.com/

- Raw text -