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Re: variadic function

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Tim Rentsch <txr@alumni.caltech.edu> writes:
> Keith Thompson <kst-u@mib.org> writes:
>
>> [snip]
>>
>> If the standard did have the requirement you mention: "Do not call
>> va_end after va_start unless va_arg has been called to process
>> every argument in the calling sequence", what great inconvenience
>> would it cause?
>
> The problem is it requires us to know things that we may
> not know, namely, the number and types of arguments remaining.
> Even if a motivating example isn't immediately obvious, that's
> a chilling prospect.

The quoted discussion was a while ago, but I think what I had in mind is
that calling va_end "too soon" would have undefined behavior.  For
example (assuming printf uses the <stdarg.h> mechanism), this:

    printf("%s\n", "arg1", "ignored");

has well defined behavior; with the hypothetical rule, its behavior
would be undefined.  If the language were changed in this way, no
implementations would have to change; the existing behavior would still
be conforming.

I do not advocate such a change; I was merely speculating on the
consequences if the language had been defined that way from the
beginning (or at least from 1989).  As I wrote before, passing excess
arguments to a variadic function is almost certainly a programming
error; making such a call's behavior undefined would not be a great
burden.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
    Will write code for food.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

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Thread

variadic function Quentin Pope <qp19433@hotmail.NOSPAM.com> - 2011-11-05 22:32 +0000
  Re: variadic function Keith Thompson <kst-u@mib.org> - 2011-11-05 15:50 -0700
    Re: variadic function Quentin Pope <qp19433@hotmail.NOSPAM.com> - 2011-11-07 17:41 +0000
  Re: variadic function James Kuyper <jameskuyper@verizon.net> - 2011-11-05 18:53 -0400
    Re: variadic function Keith Thompson <kst-u@mib.org> - 2011-11-05 16:35 -0700
      Re: variadic function Kaz Kylheku <kaz@kylheku.com> - 2011-11-06 01:36 +0000
  Re: variadic function Kaz Kylheku <kaz@kylheku.com> - 2011-11-06 01:31 +0000
  Re: variadic function Barry Schwarz <schwarzb@dqel.com> - 2011-11-06 09:45 -0800
    Re: variadic function Keith Thompson <kst-u@mib.org> - 2011-11-06 11:38 -0800
      Re: variadic function Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-24 23:24 -0800
        Re: variadic function Keith Thompson <kst-u@mib.org> - 2012-01-25 02:54 -0800
          Re: variadic function Tim Rentsch <txr@alumni.caltech.edu> - 2012-01-31 18:22 -0800
            Re: variadic function Keith Thompson <kst-u@mib.org> - 2012-01-31 21:50 -0800
              Re: variadic function James Kuyper <jameskuyper@verizon.net> - 2012-02-01 07:55 -0500
              Re: variadic function Eric Sosman <esosman@ieee-dot-org.invalid> - 2012-02-01 08:06 -0500
                Re: variadic function Keith Thompson <kst-u@mib.org> - 2012-02-01 11:42 -0800
              Re: variadic function Willem <willem@toad.stack.nl> - 2012-02-01 16:15 +0000
                Re: variadic function Keith Thompson <kst-u@mib.org> - 2012-02-01 11:41 -0800
              Re: variadic function Shao Miller <sha0.miller@gmail.com> - 2012-02-01 13:41 -0500
                Re: variadic function blp@cs.stanford.edu (Ben Pfaff) - 2012-02-01 10:45 -0800
              Re: variadic function Tim Rentsch <txr@alumni.caltech.edu> - 2012-03-08 10:30 -0800
                Re: variadic function Keith Thompson <kst-u@mib.org> - 2012-03-08 13:57 -0800
                Re: variadic function Tim Rentsch <txr@alumni.caltech.edu> - 2012-03-09 13:10 -0800
                Re: variadic function jgk@panix.com (Joe keane) - 2012-03-11 07:56 +0000
                Re: variadic function Tim Rentsch <txr@alumni.caltech.edu> - 2012-03-11 13:01 -0700
                Re: variadic function jgk@panix.com (Joe keane) - 2012-03-12 19:04 +0000
                Re: variadic function Tim Rentsch <txr@alumni.caltech.edu> - 2012-03-13 15:05 -0700

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