() obsoleted?!

**Martijn** · Nov 14 '05, 08:32 PM

Re: () obsoleted?!

> Can somebody explain why the () function argument list with the[color=blue]
> semantics "any number of arguments of any type" has been obsoleted in
> C99? Is there a suitable replacements with the same semantics
> (something like: void f(...))?[/color]

Yes, you can use ellipses ( ... ) to indicate an unknown amount of arguments
(being zero or more), but this requires at least one known argument, so
something like this (prototype):

int f(int i, ...);

Then you use the va_ set of macros to extract the arguments. Note that some
types are converted to others and you need to have some way of knowing which
types of arguments to expect (and the compiler won't check this for you!)
You also need to include stdarg.h .

All further information is easily acquired using google.

Good luck,

--
Martijn

http://www.sereneconcepts.nl

**Zeljko Vrba** · Nov 14 '05, 08:32 PM

Re: () obsoleted?!

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In article <4247b89c$0$143 $e4fe514c@news. xs4all.nl>, Martijn wrote:[color=blue]
>
> Then you use the va_ set of macros to extract the arguments. Note that some
>[/color]
Not exactly what I'm having in mind. I had the situation like this (when
writing a language interpreter).

void interpret(void)
{
void (*op)();

while(1) {
/* fetch opcode and initialize op based on it */
op(arg1, arg2, ...);
}
}

Then each of the called-by-op functions had their real definition like:

void op1(int);
void op2(int, int);
void op3(int, double);
etc.

the interpreter loop is always calling via the pointer with correct number and
types of arguments.

In this case I didn't have to mess around with va_ macros, and everything
was 'cleaner'... Now the () feature is obsoleted in C99 with nothing to
replace it in future version of the standard...

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**Robert Bachmann** · Nov 14 '05, 08:32 PM

Re: () obsoleted?!

Zeljko Vrba wrote:[color=blue]
> Can somebody explain why the () function argument list with the semantics
> "any number of arguments of any type" has been obsoleted in C99? Is there a
> suitable replacements with the same semantics (something like: void f(...))?[/color]

AFAIK void f(...); wasn't a valid declaration in C89 either.
See http://www.eskimo.com/~scs/C-faq/q15.9.html:

| Question 15.9
|
| My compiler isn't letting me declare a function
|
| int f(...)
| {
| }
| i.e. with no fixed arguments.
|
| Standard C requires at least one fixed argument,
| in part so that you can hand it to va_start.
|
| References: ANSI Sec. 3.5.4, Sec. 3.5.4.3, Sec. 4.8.1.1
| ISO Sec. 6.5.4, Sec. 6.5.4.3, Sec. 7.8.1.1

--
Robert Bachmann <news@rbach.pri v.at>, PGP-Key ID: 0x8994A748

**pjp@plauger.com** · Nov 14 '05, 08:32 PM

Re: () obsoleted?!

>> Can somebody explain why the () function argument list with the
semantics
"any number of arguments of any type" has been obsoleted in C99?

[pjp] No. I just looked at the C99 Standard and it appears to still be
there. IIRC, the only thing that went away in this area was the ability
to call a function that had not been declared.

P.J. Plauger
Dinkumware, Ltd.

503 Service Unavailable

http://www.dinkumware.com

**Andrey Tarasevich** · Nov 14 '05, 08:33 PM

Re: () obsoleted?!

Zeljko Vrba wrote:[color=blue]
> ...
> In this case I didn't have to mess around with va_ macros, and everything
> was 'cleaner'... Now the () feature is obsoleted in C99 with nothing to
> replace it in future version of the standard...
> ...[/color]

What exactly do you mean by this? C99 refers to non-prototype function
declarations as an "obsolescen t feature". C89/90 refers to this feature
in exactly the same way. Nothing changed in this respect from C89/90 to
C99. Yet you are complaining about some change in C99. What change are
you talking about?

--
Best regards,
Andrey Tarasevich

**Zeljko Vrba** · Nov 14 '05, 08:34 PM

Re: () obsoleted?!

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In article <1112010684.373 410.221930@g14g 2000cwa.googleg roups.com>, pjp@plauger.com wrote:[color=blue]
>
> [pjp] No. I just looked at the C99 Standard and it appears to still be
> there. IIRC, the only thing that went away in this area was the ability
> to call a function that had not been declared.
>[/color]
Look at the following link:

makecontext

http://www.opengroup.org/onlinepubs/009695399/functions/makecontext.html

And quotes from the rationale:

"With the incorporation of the ISO/IEC 9899:1999 standard into this
specification it was found that the ISO C standard (Subclause 6.11.6)
specifies that the use of function declarators with empty parentheses is
an obsolescent feature."

"There is no way in the ISO C standard to specify a non-obsolescent function
prototype indicating that a function will be called with an arbitrary number
(including zero) of arguments of arbitrary types (including integers, pointers
to data, pointers to functions, and composite types)."

While it did not go away, it is marked obsoleted. That was my only original
claim. Which this paragraph expresses puts more succintly and clearly. And
the question, of course, remains: why it was obsoleted?

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**Keith Thompson** · Nov 14 '05, 08:34 PM

Re: () obsoleted?!

Zeljko Vrba <first.last@oss .unist.hr> writes:[color=blue]
> In article <1112010684.373 410.221930@g14g 2000cwa.googleg roups.com>,
> pjp@plauger.com wrote:[color=green]
>>
>> [pjp] No. I just looked at the C99 Standard and it appears to still be
>> there. IIRC, the only thing that went away in this area was the ability
>> to call a function that had not been declared.
>>[/color]
> Look at the following link:
> http://www.opengroup.org/onlinepubs/...kecontext.html
>
> And quotes from the rationale:
>
> "With the incorporation of the ISO/IEC 9899:1999 standard into this
> specification it was found that the ISO C standard (Subclause 6.11.6)
> specifies that the use of function declarators with empty parentheses is
> an obsolescent feature."
>
> "There is no way in the ISO C standard to specify a non-obsolescent
> function prototype indicating that a function will be called with an
> arbitrary number (including zero) of arguments of arbitrary types
> (including integers, pointers to data, pointers to functions, and
> composite types)."
>
> While it did not go away, it is marked obsoleted. That was my only original
> claim. Which this paragraph expresses puts more succintly and clearly. And
> the question, of course, remains: why it was obsoleted?[/color]

"Obsolescen t" does not been obsolete. It merely means that it could
(not necessarily that it will) become obsolete in a future standard.

C90 6.9.4 says:

The use of function declarators with empty parentheses (not
prototype-format parameter type declarators) is an obsolescent
feature.

C99 6.11.6 says exactly the same thing:

The use of function declarators with empty parentheses (not
prototype-format parameter type declarators) is an obsolescent
feature.

The feature is still fully supported by the C90 and C99 standards.

--
Keith Thompson (The_Other_Keit h) kst-u@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

**CBFalconer** · Nov 14 '05, 08:34 PM

Re: () obsoleted?!

Zeljko Vrba wrote:[color=blue]
>[/color]
.... snip ...[color=blue]
>
> And quotes from the rationale:
>[/color]
.... snip ...[color=blue]
>
> "There is no way in the ISO C standard to specify a non-obsolescent
> function prototype indicating that a function will be called with
> an arbitrary number (including zero) of arguments of arbitrary
> types (including integers, pointers to data, pointers to functions,
> and composite types)."
>
> While it did not go away, it is marked obsoleted. That was my only
> original claim. Which this paragraph expresses puts more succintly
> and clearly. And the question, of course, remains: why it was
> obsoleted?[/color]

Because it is a security risk and doesn't prevent writing any
correct code. You always have varargs and its insecurities
available. It should be obvious that the requirement for one known
parameter is not a bind, since such is necessary to transfer
information about any further parameters in all cases.

--
"If you want to post a followup via groups.google.c om, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson

**Andrey Tarasevich** · Nov 14 '05, 08:34 PM

Re: () obsoleted?!

Zeljko Vrba wrote:[color=blue][color=green]
>>[/color]
> Look at the following link:
> http://www.opengroup.org/onlinepubs/...kecontext.html
>
> And quotes from the rationale:
>
> "With the incorporation of the ISO/IEC 9899:1999 standard into this
> specification it was found that the ISO C standard (Subclause 6.11.6)
> specifies that the use of function declarators with empty parentheses is
> an obsolescent feature."[/color]

I don't know why ISO/IEC 9899:1999 is mentioned there. As it was said
before, this type of declaration was referred to as "obsolescen t" in the
C89/90 standard as well. Nothing really changed in C99. Apparently,
authors of the above document didn't know this fact. Instead of taking a
minute to verify it they jumped to conclusion that this was a new
addition to C99.
[color=blue]
> That was my only original
> claim. Which this paragraph expresses puts more succintly and clearly. And
> the question, of course, remains: why it was obsoleted?[/color]

It probably become obsolescent "in transition" from K&R to C89/90 as
something that falls into the same family as K&R-style function
definitions (which are also obsolescent).

--
Best regards,
Andrey Tarasevich

**Peter Nilsson** · Nov 14 '05, 08:35 PM

Re: () obsoleted?!

CBFalconer wrote:[color=blue]
> Zeljko Vrba wrote:[color=green]
> > Re: () obsoleted?!
> >
> > While it did not go away, it is marked obsoleted. That was my
> > only original claim. Which this paragraph expresses puts more
> > succintly and clearly. And the question, of course, remains:
> > why it was obsoleted?[/color]
>
> Because it is a security risk and doesn't prevent writing any
> correct code. You always have varargs and its insecurities
> available. It should be obvious that the requirement for one
> known parameter is not a bind, since such is necessary to
> transfer information about any further parameters in all cases.[/color]

Hmmm...

I wouldn't say in _all_ cases. One has to ask why function macros
can be declared identifier(...) in C99, but functions can't.

C++ allows (...) functions as a 'catch all'.

It's not beyond possibility that C programmers have occasionally
wished for such a facility to be available in C. Of course, C
doesn't have function overloading, so the need is considerably
less.

But that doesn't mean the requirement for one known parameter in
variadic functions is ("obviously" ) _never_ a bind. (IMO)

--
Peter

**CBFalconer** · Nov 14 '05, 08:35 PM

Re: () obsoleted?!

Peter Nilsson wrote:[color=blue]
>[/color]
.... snip ...[color=blue]
>
> But that doesn't mean the requirement for one known parameter in
> variadic functions is ("obviously" ) _never_ a bind. (IMO)[/color]

Because you have to be able to transmit something in order to
describe how many things are being transmitted. It's not a bind
because it is absolutely necessary.

--
"If you want to post a followup via groups.google.c om, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson

**Peter Nilsson** · Nov 14 '05, 08:35 PM

Re: () obsoleted?!

CBFalconer wrote:[color=blue]
> Peter Nilsson wrote:[color=green]
> >[/color]
> ... snip ...[color=green]
> >
> > But that doesn't mean the requirement for one known parameter
> > in variadic functions is ("obviously" ) _never_ a bind. (IMO)[/color]
>
> Because you have to be able to transmit something in order to
> describe how many things are being transmitted.[/color]

What if the function wants to ignore all the parameters and
do nothing?
[color=blue]
> It's not a bind because it is absolutely necessary.[/color]

Why?

[The discussion (snipped above) is why the standard says
it is necessary for functions. It isn't necessary for
function macros in C99.]

--
Peter

**Ben Pfaff** · Nov 14 '05, 08:35 PM

Re: () obsoleted?!

CBFalconer <cbfalconer@yah oo.com> writes:
[color=blue]
> Peter Nilsson wrote:[color=green]
>> But that doesn't mean the requirement for one known parameter in
>> variadic functions is ("obviously" ) _never_ a bind. (IMO)[/color]
>
> Because you have to be able to transmit something in order to
> describe how many things are being transmitted. It's not a bind
> because it is absolutely necessary.[/color]

It is not absolutely necessary, e.g. I can pass a null-terminated
list of pointers.
--
"Some programming practices beg for errors;
this one is like calling an 800 number
and having errors delivered to your door."
--Steve McConnell

**Arthur J. O'Dwyer** · Nov 14 '05, 08:35 PM

Re: () obsoleted?!

On Tue, 29 Mar 2005, Ben Pfaff wrote:[color=blue]
> CBFalconer <cbfalconer@yah oo.com> writes:[color=green]
>> Peter Nilsson wrote:[color=darkred]
>>> But that doesn't mean the requirement for one known parameter in
>>> variadic functions is ("obviously" ) _never_ a bind. (IMO)[/color]
>>
>> Because you have to be able to transmit something in order to
>> describe how many things are being transmitted. It's not a bind
>> because it is absolutely necessary.[/color]
>
> It is not absolutely necessary, e.g. I can pass a null-terminated
> list of pointers.[/color]

Even a null-terminated list has to contain at least one element (namely,
a null pointer). I agree with CBFalconer in practice, but with the other
side in theory; certainly there's nothing intrinsically /wrong/ with

void foo(...) {
/* ignore all arguments and */ return;
}

or even [UNTESTED PSEUDO-C]

int bar_type;
int bar(...) {
va_list ap;
va_start(ap);
switch (bar_type) { /* set by the user before this call */
case 0: printf("%d", va_arg(ap, int)); break;
case 1: printf("%s", va_arg(ap, const char*)); break;
case 2: printf("%g", va_arg(ap, double)); break;
}
va_end(ap);
return bar_type;
}

The standard just arbitrarily disallows such constructions. I think
the restriction has absolutely no effect on /real-world/ programs, but
it is kind of weird and non-orthogonal, if you ask me.

my $.02,
-Arthur