Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-tis!ames!oliveb!sun!thetone!swilson
From: swilson%thetone@Sun.COM (Scott Wilson)
Newsgroups: comp.lang.c
Subject: Re: QuickC
Message-ID: <65868@sun.uucp>
Date: 26 Aug 88 20:01:01 GMT
References: <8808261424.AA11504@ucbvax.Berkeley.EDU>
Sender: news@sun.uucp
Reply-To: swilson@sun.UUCP (Scott Wilson)
Organization: Sun Microsystems, Mountain View
Lines: 35

In article <8808261424.AA11504@ucbvax.Berkeley.EDU> TURGUT@TREARN.BITNET (Turgut Kalfaoglu) writes:
>main()
>{
>   int a,v;
>   a = 2;
>   v = square(a);
>   printf("%d\n",v);
>}
>
>square(num)
>int num;
>{
>  num = num*num;
>}
>WHY does it work?

I get the same behavior on a Sun running 3.5 (but not 4.0).  The reason
it works is that the scratch register used for the multiplication happens
to be the same register that is used to return the function's value (in
my case d0).  The reason that adding the assignment to dummy didn't change
anything is that this most likely didn't involve any registers, the value
was stored directly in memory since dummy is on the stack.

Under SunOS 4.0 this gives the answer 0.  For some reason all functions
without an explicit return statement return 0.  I think it has something
to do with compatibility with 4.3 BSD where return(x) in main() is the
same as exit(x).  Since main() often ends without a return (or exit()
being called) it could cause problems if a random register value were used
for the exit code.  So, main() without a return returns zero which is
a "successfull" termination in UNIX.


--
Scott Wilson		arpa: swilson@sun.com
Sun Microsystems	uucp: ...!sun!swilson
Mt. View, CA