Path: utzoo!attcan!uunet!taumet!steve
From: steve@taumet.com (Stephen Clamage)
Newsgroups: comp.lang.c
Subject: Re: 'void' arguments (Yet Another Feature Proposal)
Message-ID: <565@taumet.com>
Date: 23 Jan 91 16:15:48 GMT
References: <943@tuura.UUCP>
Distribution: comp
Organization: Taumetric Corporation, San Diego
Lines: 45

risto@tuura.UUCP (Risto Lankinen) writes:

>Suppose there's function...

>   SetThisMode( int iMode,int iValue1,int iValue2,int iValue3 );

>also suppose the documentation says that 'when iMode==<xyz>, then none of
>the iValue:s have any effect'.  In code you'd then write:

>   SetThisMode( <xyz>,0,0,0 ); or SetThisMode( <xyz>,<your-age-in-days>,
>      <temperature-in-Kelvins>,<number-of-emptied-Coke-cans-this-week> );

>when you could be doing...

>   SetThisMode( <xyz>,(int)any,(int)any,(int)any );

>where the 'any' is my proposal for a keyword (as promised in the header).
>It could be any other, too, for that matter - I actually tried some 'void'
>derivatives, to check out whether there already were a legal way to do so.

This problem is already solved in two different ways in C++.

1.  Default parameters.  You may specify default values for any (or all)
trailing parameters in the prototype.  Any of the rightmost parameters
with default values may be omitted in a call:
	SetThisMode( int iMode, int iValue1=0, int iValue2=0, int iValue3=0);
can be called as any of
	SetThisMode(fee>);
	SetThisMode(fie>, 1);
	SetThisMode(foh>, 1, 2);
	SetThisMode(fum>, 1, 2, 3);
This does not address your efficiency concern.

2.  Overloaded functions.  You may define more than one function with the
same name, as long as their calling sequences are different:
	SetThisMode( int iMode);
	SetThisMode( int iMode, int iValue1);
	SetThisMode( int iMode, int iValue1, int iValue2);
	SetThisMode( int iMode, int iValue1, int iValue2, int iValue3);
The compiler calls version of the function with the matching calling sequence.
Since only the supplied parameters are passed, you get the most efficient
possible call.
-- 

Steve Clamage, TauMetric Corp, steve@taumet.com