Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!uunet!mcsun!ukc!edcastle!aiai!richard
From: richard@aiai.ed.ac.uk (Richard Tobin)
Newsgroups: comp.lang.c
Subject: Re: ANSI C questions (parameters, structure assignment)
Message-ID: <3278@skye.ed.ac.uk>
Date: 23 Aug 90 16:45:20 GMT
References: <1081.26d26274@desire.wright.edu>
Reply-To: richard@aiai.UUCP (Richard Tobin)
Organization: AIAI, University of Edinburgh, Scotland
Lines: 33

In article <1081.26d26274@desire.wright.edu> demon@desire.wright.edu writes:
>	1)	In standard C, when you pass a structure bigger than four
>longwords, is the structure passed as a value parameter, or just a pointer to
>the structure (thus making it a var parameter)?

Structures are passed by value regardless of their size.

Whether this is implemented by actually putting the structure on the
stack, or by passing a pointer to a copy of it, is invisible to the
programmer.

[Actually, it's only invisible to the *correct* programmer.  I recently
forgot to put "&" before the name of a structure I was passing.  This
made no difference on a Sun 4 (which passes the structure by putting
the address in a register) and I didn't discover the error until I
compiled it on a Sun 3.]

>	2)	Are structure assignments allowed only for initializations

No.  Structure assignments are fine in ANSI C.

>struct_thing -= still_more_struct;
>struct_thing *= even_more_struct;

But I don't know what these are supposed to mean.  What do you expect
subtracting structures to do?

-- Richard

-- 
Richard Tobin,                       JANET: R.Tobin@uk.ac.ed             
AI Applications Institute,           ARPA:  R.Tobin%uk.ac.ed@nsfnet-relay.ac.uk
Edinburgh University.                UUCP:  ...!ukc!ed.ac.uk!R.Tobin