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

["mrs at apple dot com" <gcc-bugzilla at gcc dot gnu dot org>]

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