Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!lll-winken!uunet!mitel!sce!sunray!jimp
From: jimp@sunray.UUCP (Jim Patterson)
Newsgroups: comp.lang.c
Subject: Re: printf() problem
Keywords: C printf
Message-ID: <6006@sunray.UUCP>
Date: 29 Apr 89 20:43:54 GMT
References: <11657@hodge.UUCP> <89Apr26.092233edt.18850@me.utoronto.ca>
Reply-To: jimp@cognos.UUCP (Jim Patterson)
Organization: Cognos Inc., Ottawa, Canada
Lines: 20

In article <89Apr26.092233edt.18850@me.utoronto.ca> zougas@hammer.me.UUCP (Athanasios(Tom) Zougas) writes:
>C puts its function parameters on the stack in "reverse" order, i.e.
>the last item is on top (this allows variable number of parameters
>for user defined functions). It would happen in any C.

It doesn't happen in "any" C.  While reverse order is commonly chosen
by C implementations, in fact the order is deliberately left
unspecified by the language.  Other implementations will choose to
evaluate parameters in first to last order, or they could use first,
third, fourth, second in a given instance, etc.  A good compiler
might generate two results in registers, in order, and push them with
a single instruction. (I think the VAX/VMS C compiler might actually
do this using a VAX PUSHQ instruction). In short, don't rely on
evaluation order (and in particular avoid side-effect dependencies
like in the printf(getc(),getc()) example).
-- 
Jim Patterson                              Cognos Incorporated
UUCP:decvax!utzoo!dciem!nrcaer!cognos!jimp P.O. BOX 9707    
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