void argument

[PengYu.UT@gmail.com]

Hi,

I know that there is a difference (in C) between

int fun(void);

int fun();

The first one takes no arguments. The second can take any number of
arguments, including 0.

I'm wondering if this difference is still hold in C++.

Thanks,
Peng

[Jacques Labuschagne]

Re: void argument

PengYu.UT@gmail .com wrote:[color=blue]
> Hi,
>
> I know that there is a difference (in C) between
>
> int fun(void);
>
> int fun();
>
> The first one takes no arguments. The second can take any number of
> arguments, including 0.
>
> I'm wondering if this difference is still hold in C++.[/color]

Nope, they're exactly the same thing in C++: fun takes no arguments. For
a function taking any number of arguments use ellipses, e.g. void fun(...);

Jacques.

[Cy Edmunds]

Re: void argument

<PengYu.UT@gmai l.com> wrote in message
news:1128811195 .034220.292210@ g44g2000cwa.goo glegroups.com.. .[color=blue]
> Hi,
>
> I know that there is a difference (in C) between
>
> int fun(void);
>
> int fun();
>
> The first one takes no arguments. The second can take any number of
> arguments, including 0.
>
> I'm wondering if this difference is still hold in C++.
>
> Thanks,
> Peng
>[/color]

No, in C++ they mean the same: a function which takes no arguments. The
business about taking any number of arguments is disallowed in C++. Because
of overloading, the argument types are part of the function's signature.

--
Cy

http://home.rochester.rr.com/cyhome/

[Nan Li]

Re: void argument

No.

[nan@athena test]$ cat test2.c
void foo()
{
}
int main()
{
foo(1,2);
return 1;
}
[nan@athena test]$ g++ -Wall -x c test2.c
[nan@athena test]$ g++ -Wall -x c++ test2.c
test2.c: In function `int main()':
test2.c:2: error: too many arguments to function `void foo()'
test2.c:7: error: at this point in file

[Chris Hills]

Re: void argument

In article <1128812307.838 583.9210@f14g20 00cwb.googlegro ups.com>, Nan Li
<nan.li.g@gmail .com> writes[color=blue]
>No.[/color]

No what?

If you are replying top something quote the message you are replying to.

If you are using the broken google interface to usenet please set the
options properly.




--
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
\/\/\/\/\ Chris Hills Staffs England /\/\/\/\/
/\/\/ chris@phaedsys. org www.phaedsys.org \/\/\
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/

[ben]

Re: void argument

PengYu.UT@gmail .com wrote:[color=blue]
> Hi,
>
> I know that there is a difference (in C) between
>
> int fun(void);
>
> int fun();
>
> The first one takes no arguments. The second can take any number of
> arguments, including 0.
>
> I'm wondering if this difference is still hold in C++.
>
> Thanks,
> Peng
>[/color]


No. In C++, the above two prototypes are exactly the same.

Ben

[Clark S. Cox III]

Re: void argument

On 2005-10-08 18:48:19 -0400, Jacques Labuschagne
<jacques@clawsh rimp.com> said:
[color=blue]
> PengYu.UT@gmail .com wrote:[color=green]
>> Hi,
>>
>> I know that there is a difference (in C) between
>>
>> int fun(void);
>>
>> int fun();
>>
>> The first one takes no arguments. The second can take any number of
>> arguments, including 0.
>>
>> I'm wondering if this difference is still hold in C++.[/color]
>
> Nope, they're exactly the same thing in C++: fun takes no arguments.
> For a function taking any number of arguments use ellipses, e.g. void
> fun(...);[/color]

Actually, no. You cannot define a function taking any number of
arguments that way. Using the ellipsis (even in C), requires at least
one non variadic parameter, i.e.:

/* This function requires at least one int argument, but can take any
number of additional, non-POD arguments */
void fun(int, ...)
{
}

/* This function definition is illegal:*/
void fun2(...)
{
}

--
Clark S. Cox, III
clarkcox3@gmail .com

[Alf P. Steinbach]

Re: void argument

* Clark S. Cox III:[color=blue]
> On 2005-10-08 18:48:19 -0400, Jacques Labuschagne
> <jacques@clawsh rimp.com> said:
>[color=green]
> > PengYu.UT@gmail .com wrote:[color=darkred]
> >> Hi,
> >>
> >> I know that there is a difference (in C) between
> >>
> >> int fun(void);
> >>
> >> int fun();
> >>
> >> The first one takes no arguments. The second can take any number of
> >> arguments, including 0.
> >>
> >> I'm wondering if this difference is still hold in C++.[/color]
> >
> > Nope, they're exactly the same thing in C++: fun takes no arguments.
> > For a function taking any number of arguments use ellipses, e.g. void
> > fun(...);[/color]
>
> Actually, no. You cannot define a function taking any number of
> arguments that way. Using the ellipsis (even in C), requires at least
> one non variadic parameter, i.e.:[/color]

Not in C++ (I don't know about C).

There are two forms of parameter-declaration-clause,

parameter-declaration-list[OPT] ...[OPT]
parameter-declaration-list, ...

It seems you've focused only the second form.

You might ask, what would something like void foo(...){} be good for, since
there's no argument there to anchor the argument retrieval?

And one answer is that the ellipsis ... ranks lowest of all possible matches
for an actual argument, and for this usage it would just be silly to require
an extra argument in front.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[Branimir Maksimovic]

Re: void argument


<PengYu.UT@gmai l.com> wrote in message
news:1128811195 .034220.292210@ g44g2000cwa.goo glegroups.com.. .[color=blue]
> Hi,
>
> I know that there is a difference (in C) between
>
> int fun(void);
>
> int fun();
>
> The first one takes no arguments. The second can take any number of
> arguments, including 0.
>
> I'm wondering if this difference is still hold in C++.[/color]

No, and that is a very good thing.
When I was C beginner, that lack of prototyping in C was a real problem
for me (and I dind't know that one should always prototype functions
back in 1987.).

int main()
{
int i = malloc(32);
int *p = malloc(32);
free(i);
free(p);
return 0;
}

This C code compiles and links without problem, but causes lot of trouble.

Greetings, Bane.

[Rolf Magnus]

Re: void argument

Alf P. Steinbach wrote:
[color=blue]
> You might ask, what would something like void foo(...){} be good for,
> since there's no argument there to anchor the argument retrieval?[/color]

My question would be how to retrieve the arguments, since va_start needs the
last fixed argument, which in this case doesn't exist.

[Bob Hairgrove]

Re: void argument

On Sun, 09 Oct 2005 00:53:30 GMT, alfps@start.no (Alf P. Steinbach)
wrote:
[color=blue]
>You might ask, what would something like void foo(...){} be good for, since
>there's no argument there to anchor the argument retrieval?[/color]

I've only seen this syntax used in catch statements (i.e. as a
"catch-all" last resort). It is sometimes dangerous, though --
depending on the platform, it could be a source of memory leaks if
used indiscriminatel y.

--
Bob Hairgrove
NoSpamPlease@Ho me.com

[Alf P. Steinbach]

Re: void argument

* Rolf Magnus:[color=blue]
> Alf P. Steinbach wrote:
>[color=green]
> > You might ask, what would something like void foo(...){} be good for,
> > since there's no argument there to anchor the argument retrieval?[/color]
>
> My question would be how to retrieve the arguments, since va_start needs the
> last fixed argument, which in this case doesn't exist.[/color]

That's the same question; already answered. ;-)

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[Jay Nabonne]

Re: void argument

On Sat, 08 Oct 2005 15:58:27 -0700, Nan Li wrote:
[color=blue]
> No.
>
> [nan@athena test]$ cat test2.c
> void foo()
> {
> }
> int main()
> {
> foo(1,2);
> return 1;
> }
> [nan@athena test]$ g++ -Wall -x c test2.c
> [nan@athena test]$ g++ -Wall -x c++ test2.c
> test2.c: In function `int main()':
> test2.c:2: error: too many arguments to function `void foo()'
> test2.c:7: error: at this point in file[/color]

There's a difference between a function prototype ("declaratio n") and a
function definition.

Change the above "foo" to:

extern void foo();

and it will work fine. The assumption is that there is a real function
somewhere that has some sort of arguments. The danger is you're not
matching the real argument definition, so the compiler has to guess based
on the arguments you pass.

Of course, that's all C, so I may have a detail or two wrong...

- Jay

[Branimir Maksimovic]

Re: void argument


"Jay Nabonne" <jay_nabonne@so nicNOSPAM.com> wrote in message
news:pan.2005.1 0.09.19.55.51.1 6000@sonicNOSPA M.com...[color=blue]
> On Sat, 08 Oct 2005 15:58:27 -0700, Nan Li wrote:
>[color=green]
>> No.
>>
>> [nan@athena test]$ cat test2.c
>> void foo()
>> {
>> }
>> int main()
>> {
>> foo(1,2);
>> return 1;
>> }
>> [nan@athena test]$ g++ -Wall -x c test2.c
>> [nan@athena test]$ g++ -Wall -x c++ test2.c
>> test2.c: In function `int main()':
>> test2.c:2: error: too many arguments to function `void foo()'
>> test2.c:7: error: at this point in file[/color]
>
> There's a difference between a function prototype ("declaratio n") and a
> function definition.
>
> Change the above "foo" to:
>
> extern void foo();
>
> and it will work fine. The assumption is that there is a real function
> somewhere that has some sort of arguments. The danger is you're not
> matching the real argument definition, so the compiler has to guess based
> on the arguments you pass.
>
> Of course, that's all C, so I may have a detail or two wrong...[/color]

function definition with empty parenthesis in c also means no arguments.
this is valid only for declaration, so you are right, but g++ would compile
it
as c++ anyway; one must use gcc for c compiling.

void foo();

int main()
{
foo(1);
foo(1,'c',3.2);
return 0;
}

void foo()
{
}

compiles with no problem in c.

Greetings, Bane.