Objects in var. length arguments (?)

[Alvaro Segura]

Hello,

I have this doubt that I find no answer for:

Can an object or a reference to an object be passed as an argument to a
variable length arguments function? And if so, how does it work?

// suppose we have:
void f(int x, ...);
class A {};

// and we do:
A a;
f(3, a); // is this OK?

I recently found that MSVC++ was not complaining when I accidentally did
something like that, but I thought it was wrong. What about the standard?

[Michael Kochetkov]

Re: Objects in var. length arguments (?)


"Alvaro Segura" <asegura.NO_SPA M_@vicomtech.es > wrote in message
news:bod9vo$902 $2@unbe.sarenet .es...[color=blue]
> Hello,
>
> I have this doubt that I find no answer for:
>
> Can an object or a reference to an object be passed as an argument to a
> variable length arguments function? And if so, how does it work?
>
> // suppose we have:
> void f(int x, ...);
> class A {};
>
> // and we do:
> A a;
> f(3, a); // is this OK?
>
> I recently found that MSVC++ was not complaining when I accidentally did
> something like that, but I thought it was wrong. What about the standard?[/color]
Your code is OK. It is the f's problem to find A object on the stack. The
common solution is to pass a kind of a format information to f.

--
Michael Kochetkov.

[Ron Natalie]

Re: Objects in var. length arguments (?)


"Michael Kochetkov" <Michael.Kochet kov@synartra.co mmmm> wrote in message news:3faa6e4a@n ews.telekom.ru. ..
[color=blue]
> Your code is OK. It is the f's problem to find A object on the stack. The
> common solution is to pass a kind of a format information to f.[/color]

In this case, since A is of POD type, it is ok.
Had the class A been been a little bit more elaborate (so as to make it non-POD)
it would have been undefined behavior.

[Victor Bazarov]

Re: Objects in var. length arguments (?)

"Alvaro Segura" <asegura.NO_SPA M_@vicomtech.es > wrote...[color=blue]
> I have this doubt that I find no answer for:
>
> Can an object or a reference to an object be passed as an argument to a
> variable length arguments function? And if so, how does it work?[/color]

An object can, but only if the object is of POD type. A reference
probably cannot.
[color=blue]
> // suppose we have:
> void f(int x, ...);
> class A {};
>
> // and we do:
> A a;
> f(3, a); // is this OK?[/color]

Yes, class A is a POD.
[color=blue]
> I recently found that MSVC++ was not complaining when I accidentally did
> something like that, but I thought it was wrong. What about the standard?[/color]

The Standard says that if it's not POD, the behaviour is undefined.
See 5.2.2/7.

Victor