[Bug c++/55453] New: Bug with virtual methods and objects with dtors.

[blitzmunter at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55453

             Bug #: 55453
           Summary: Bug with virtual methods and objects with dtors.
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: blitzmunter@gmail.com


Hi,

Mingw G++ appears to have a bug involving multiple inheritance and virtual
methods that return objects with dtors.

I have tried on 3 ditros - nuwen, tdm and the official mingw distro - and it
happens on all g++ versions >= 4.7.0.

It does not appear to occur on Linux, although I've only been able to test with
kubuntu12 and mint14, both of which have g++ 4.7.2 installed.

Even though this appears to be mingw specific, I've already posted this bug
report on the mingw bug reports system and they told me to post it here.

Anyway, see below code: The problem occurs when the 'interface method'
LinkResolver is called by the markdown object. The correct method is invoked,
but the 'this' pointer is messed up.

The trigger seems to be the String dtor. Remove this, or have the interface
method return a simple type, and it works as expected.

Bye!
Mark

//***** CODE ******

#include <stdio.h>

struct String {
    ~String() { }
};

struct Object {
    virtual ~Object() { }
};

struct LinkResolver {
    virtual String ResolveLink() = 0;
};

struct Docs : public Object, public virtual LinkResolver {
    Docs() {
        printf("       Docs::Docs() this: %p\n", this);
    }

    virtual String ResolveLink() {
        printf("Docs::ResolveLink() this: %p\n", this);
        return String();
    }
};

struct Markdown {
    LinkResolver * _resolver;

    Markdown(LinkResolver * resolver) : _resolver(resolver) { }

    void Go() {
        _resolver->ResolveLink();
    }
};

int main() {
    printf("GCC %d.%d.%d\n", __GNUC__, __GNUC_MINOR__, __GNUC_PATCHLEVEL__);

    Docs d;

    printf("             main()   &d: %p\n", &d);

    d.ResolveLink();

    Markdown m(&d);

    m.Go();
}