[Bug c++/25316] New: POD structures can have

[Bug c++/25316] New: POD structures can have

[mrs at apple dot com]

A user reported that this:

mrs $ cat > t98.c
        struct X {
                int a, b;
                X() : a(0), b(0) {}
        };

        static void f(const char *s, ...);

        int main()
        {
                X x;
                f("foo!", x);
                return 0;
        }

works on other C++ compilers (Metroworks), but on gcc:

mrs $ ./g++ -B./ -c t98.c
t98.c: In function 'int main()':
t98.c:11: warning: cannot pass objects of non-POD type 'struct X' through
'...'; call will abort at runtime

This, according the a reading of the standard is a POD type, no, really.  :-) 
Curious though, the same misreading of the text was done by the author of:

3 It is possible to transfer into  a  block,  but  not  in  a  way  that
  bypasses declarations with initialization.  A  program  that  jumps77)
  from a point where a local variable with automatic storage duration is
  not in scope to a point where it is in scope is ill-formed unless  the
  variable  has POD type (_basic.types_) and is declared without an ini-
  tializer (_dcl.init_).

as the intent was to not bypass a constructor call.

Also curious is the wording:

  To default-initialize an object of type T means:

  --if T is a non-POD class type (clause _class_), the default construc-
    tor  for  T is called (and the initialization is ill-formed if T has
    no accessible default constructor);

which again reinforces the idea that only non-PODs can have default
constructors called.

Seems like we need a DR to clarify this, if one doesn't aready exist, and then
to fix up the compiler, if any fixups need to be done.  I'd expect that the
compiler behavior is correct, but until DRed.


-- 
           Summary: POD structures can have
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mrs at apple dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25316

[Bug c++/25316] POD structures can have

[mrs at apple dot com]

------- Comment #1 from mrs at apple dot com  2005-12-08 20:51 -------
Ah, Geoff found it:

  The definition of 'aggregate' is in 8.5.1

I new it was there someplace.


-- 

mrs at apple dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID
            Summary|POD structures can have     |POD structures can have


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25316

[Bug c++/25316] POD structures can have

[gdr at integrable-solutions dot net]

------- Comment #2 from gdr at integrable-solutions dot net  2005-12-08 22:25 -------
Subject: Re:   New: POD structures can have

"mrs at apple dot com" <gcc-bugzilla@gcc.gnu.org> writes:

| A user reported that this:
| 
| mrs $ cat > t98.c
|         struct X {
|                 int a, b;
|                 X() : a(0), b(0) {}
|         };
| 
|         static void f(const char *s, ...);
| 
|         int main()
|         {
|                 X x;
|                 f("foo!", x);
|                 return 0;
|         }
| 
| works on other C++ compilers (Metroworks), but on gcc:
| 
| mrs $ ./g++ -B./ -c t98.c
| t98.c: In function 'int main()':
| t98.c:11: warning: cannot pass objects of non-POD type 'struct X' through
| '...'; call will abort at runtime
| 
| This, according the a reading of the standard is a POD type, no, really.  :-) 

Are you saying "struct X" is a POD?

-- Gaby


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25316

[Bug c++/25316] POD structures can have

[mrs at apple dot com]

------- Comment #3 from mrs at apple dot com  2005-12-08 23:53 -------
As I said, the prohibition is in 8.5.1 in the definition of aggregate.  This is
what makes it not a POD.  No DR needed, no gcc bug fix needed, the bug was in
the Metroworks compiler and in the users understanding.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25316