[Bug c++/21917] New: Missing warning? (or error?)

[Bug c++/21917] New: Missing warning? (or error?)

[igodard at pacbell dot net]

struct  virt { virt() : i(2) {} virt(int i) : i(i){} int i;  };
struct der1 : public virtual virt { der1(int i) : virt(i) {} };
struct der2 : public virtual virt { der2(int i) : virt(i) {} };
struct top : public der1, public der2 {
    top () : der1(0), der2(1) {} };
int main() { top t; }


Compiles without comment. However, the null constructor for "virt" is called
rather than the explicit constructor that is indicated by the constructor chain
from top. In fact, the der* constructors say " : virt(i)" but that
sub-constructor will never be called because virt is a virtual base class.

I don't know if it is actually an error to try to explicitly construct a virtual
base, but is sure is misleading and I think deserves at least a warning.

-- 
           Summary: Missing warning? (or error?)
           Product: gcc
           Version: 3.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: igodard at pacbell dot net
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21917

[Bug c++/21917] Missing warning? (or error?)

[igodard at pacbell dot net]

------- Additional Comments From igodard at pacbell dot net  2005-06-04 22:22 -------
p.s. I suppose that if there is only a single path to the virtual base then
explicit construction is meaningful and the explicit construction in the der*
classes is not wrong. But in the constructor for "top" the compiler knows that
there are multiple derivations from virt (it has to or it couldn't know to call
the null constructor), so the warning could be issued in "top". Something like
"base constructor virt(int) in der1(int) bypassed, virt() used instead"?

Ivan

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21917

[Bug c++/21917] Missing warning? (or error?)

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-06-05 03:02 -------
This is how C++ is done, maybe a warning can be emitted but it seems like it will emitt too much for 
valid C++ code.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21917

[Bug c++/21917] Missing warning?

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|Missing warning? (or error?)|Missing warning?


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21917

[Bug c++/21917] Missing warning?

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21917

[Bug c++/21917] Missing warning?

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21917