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From: john@viper.Lynx.MN.ORG (John Stanley)
Newsgroups: comp.sys.atari.st
Subject: Re: Megamax WON'T compile .... structures passed to functions
Message-ID: <1031@viper.Lynx.MN.ORG>
Date: Fri, 22-May-87 01:44:15 EDT
Article-I.D.: viper.1031
Posted: Fri May 22 01:44:15 1987
Date-Received: Sat, 23-May-87 14:47:26 EDT
References: <280@nikhefh.UUCP>
Reply-To: john@viper.UUCP (John Stanley)
Organization: DynaSoft Systems
Lines: 56
Keywords: megamax

In article <280@nikhefh.UUCP> gert@nikhefh.UUCP (Gert Poletiek) writes:
 >
 >In response to the denial of a few persons that Megamax won't accept 
 >passing of structures to functions: The Megamax compiler will accept the C
 >code. It will not issue any warning, but the code it generates it 
 >totally wrong!

  Passing a structure to a function is not supported in the definition
of how-C-works...  Take a look in your handy dandy K&R (page 121).  It
tells you that passing structures to a function is -not-supported-.

  The compilers that have been created since then handle the problem in
(unfortunately) one of three incompatable ways...

	1)  Since K&R said it was not supported, some compilers will
	flag a structure-parameter as an error... (nuf said, next...)

	2)  Since passing a structure isn't supported in K&R C, if you
	include a structure name in a parameter list, you must really
	mean to pass the address of that structure as a pointer.  The
	compiler thus handles structure and array references in the
	exact same way.  (A few of the compilers that do this 
	(unfortunately, not megamax) go the whole route and also
	convert a structure receiver on the functions side into a
	structure pointer and converts structure references within
	the function into indirect references to match.)  Most of
	the compilers in this class assume you have a struct pointer
	in the parameter list of the function.  If you have a struct
	instead, the compiler assumes you plan to reference the
	arguments as a structure for some purpose and the references
	to the structure elements reference the individual parameters...

	3)  Some "C" compilers take your word that you do, in fact,
	want to stick a copy of the entire structure on the stack and
	pass it to the function.

  Megamax is aparently one of the class 2 structure passing compilers,
but without the (slightly illegal) conversion on the function end of
things.

  Summery:  Yes, megamax isn't handling it correctly, but then, you
can't count on any program that passes structures to work on any
randomly selected C compiler...  Apparently you learned to write C 
on a class 3 compiler.  Anything you do that involves passing 
structures will-not-work on (at a guess) 75% of all compilers.  It's 
a habit you would be better off un-learning as soon as possible.

  Solution?  When you're learning a new compiler or trying to write
portable code, make the assumption that passing a struct doesn't 
work.  Pass a pointer to the structure or to a copy of the structure 
and have a much better chance of your code being portable (and running)...

--- 
John Stanley (john@viper.UUCP)
Software Consultant - DynaSoft Systems
UUCP: ...{amdahl,ihnp4,rutgers}!{meccts,dayton}!viper!john