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From: meissner@osf.org (Michael Meissner)
Newsgroups: comp.lang.c
Subject: Re: Function returning Structure:  How does it work?
Message-ID: <MEISSNER.90May30102110@curley.osf.org>
Date: 30 May 90 14:21:10 GMT
References: <1990May28.215331.29333@agate.berkeley.edu>
	<1990May28.235336.5338@Neon.Stanford.EDU> <18222@well.sf.ca.us>
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In-reply-to: rld@well.sf.ca.us's message of 30 May 90 04:32:55 GMT

In article <18222@well.sf.ca.us> rld@well.sf.ca.us (Rick Davis) writes:

| In article <1990May28.235336.5338@Neon.Stanford.EDU>, Dave Eisen writes:
| >
| > Of course, this
| > can lead to a great deal of copying so most of the time you're better off
| > arranging things for the function to have type STRUCT * instead.
| > 
| 
| I can't agree with this too strongly.  Passing entire structures back
| and forth is almost always a serious waste of time and stack space.
| Indeed, there are circumstances where it is necessary, (i.e communications)
| but most of the time you're much better off with the structure pointer.
| Also, some implementations of C won't even let you try.  Code portability
| alone works for me.

But a clever compiler could optimize:

	struct foo func(), var;

	var = func();

and pass the address of var (assuming it returns structures by passing
a pointer as a hidden argument), so that a temporary and a structure
copy are not required.
--
Michael Meissner	email: meissner@osf.org		phone: 617-621-8861
Open Software Foundation, 11 Cambridge Center, Cambridge, MA

Catproof is an oxymoron, Childproof is nearly so