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]

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?

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.

 

[Ron Natalie]

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.

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]

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?

An object can, but only if the object is of POD type. A reference
probably cannot.

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

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

Yes, class A is a POD.

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?

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

Victor