Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!elroy.jpl.nasa.gov!decwrl!infopiz!lupine!rfg
From: rfg@NCD.COM (Ron Guilmette)
Newsgroups: comp.lang.c++
Subject: Re: Use of Ellipsis on c++
Message-ID: <5131@lupine.NCD.COM>
Date: 19 Apr 91 15:59:01 GMT
References: <1991Apr18.203147.19510@bingvaxu.cc.binghamton.edu>
Organization: Network Computing Devices, Inc., Mt. View, CA
Lines: 53

In article <1991Apr18.203147.19510@bingvaxu.cc.binghamton.edu> consp06@bingsuns.cc.binghamton.edu (Robert Konigsberg) writes:
>I'm writing my first c++ Class - Matrices (Ooooohh)
>
>The Constructor is defined as follows:
>
>void Matrix(unsigned xv=1, yv=1, ...) {Alloc(xv,yv); SetZero();
>                                       Values(...);};
>
>See?  It initializes the size in Alloc.  It sets all the values to
>zero in SetZero, and then takes the values from ... in inserts them
>into the matrix...

You have apparently uncovered an interesting bug in your C++ language
processor (which I suspect is cfront, but I'm not sure).

An ellipsis (i.e. `...') is *not*, I repeat *not* a variable nor is it
anything even remotely like a variable.  Thus, it is also not a formal
parameter and it should be illegal to try to "pass" an ellipsis to
another function.

The ellipsis is a special token whose only legitimate use is as a way
of indicating that a given function may (or may not) take additional
parameters (beyond those listed to the left of the ellipsis), all of
which have unspecified types.

In order to access these additional *actual* parameter values (if any)
you must use the va_start, va_arg, and va_end macros.  (See your local
manpage under `stdarg' or your ANSI C standard document.)

So the long and the short of it is that you have done something (i.e.
trying to "pass" an ellipsis) which is illegal in both ANSI C and in
C++.

The fact that your C++ language processor let you get away with this
indicates that there is bug in that product.

(Note that some C compilers produced by AT&T have an interesting implementation
of the va_start macro which assumes that the underlying C compiler *does*
allow one to say:

		&...

within the body of a function.  I suspect that the ability to refer to `...'
within the body of a function may have been carried over into other AT&T
products, but I have no way of knowing. Cfront 2.1 properly complains if
you try to "pass" an ellipsis.)

So what C++ language processor *are* you using?
-- 

// Ron ("Loose Cannon") Guilmette
// Internet: rfg@ncd.com      uucp: ...uunet!lupine!rfg
// New motto:  If it ain't broke, try using a bigger hammer.