Re: Passing class objects through ... with egcs (g++)

[Doug Semler <doug@seaspace.com>]

> Hi,
> 
>   I'm porting an application from AIX/xlC to Linux/g++.
> 
>   I'm using egcs-1.0.2 and am having problems compiling some functions
>   which allow class objects to be passed as variable # of arguments (...).
> 
>   I get the following compile warning:
> 
>      warning: cannot pass objects of type `XXX' through `...'
> 
>   where XXX is my class type.
> 
>   Is this something that is allowed in a newer version of egcs or is there
>   some command line option I can specify to allow this to work?
> 
>   I realize I can use function overloading to get around this but in my
>   case where different objects types may be passed, it would get real ugly.
> 
>   I notice it is just a warning. Does the compiler still correctly place
>   the entire object on the stack?

Probably not....

My guess is you're passing a non-POD class  (plain ol' data) through the
va_list...

5.2.2:
  When there is no parameter for a given argument ... ,
  if the argument ... has a non-POD class type(9), the behavior is
  undefined.

9:

 A POD-struct is an aggregate class that has no non-static data members of
 type pointer to member, non-POD-struct, non-POD-union (or array of such
 types) or reference, and has no user-defined copy assignment operator and
 no user-defined destructor.  Similarly, a POD-union is an aggregate union
 that has no non-static data members of type pointer to member, 
 non-POD-struct, non-POD-union (or array of such types) or reference, 
 and has no user-defined copy assignment operator and no user-defined
 destructor. A POD class is a class that is either a POD-struct or POD-union.

So your code may be broken;  if your class exhibits any of the above non-POD
class characteristics, it is.  Probably the reason you get the error now
is that egcs is more strict regarding the C++ standard than older versions
of gcc and more than likely, your AIX compiler :)

---
Doug Semler                       | doug@seaspace.com
SeaSpace Corporation              | Garbage In -- Gospel Out
Least Senior Software Developer;  | Minister of things to do Next Quarter
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