[Bug c++/44841] New: Add suggestion to "undefined reference to `vtable for ...´"

["phresnel at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

It was today that I stumbled over the seemingly simple situation of tweaking
some bits of an interface class. 

Upon doing that, I got an undefined reference to a vtable.

I made clean and made my application. Nothing changed. Then I checked again the
interface and didn't find anything. Then I checked all derivations. Nothing.

Of course it was just me who has been a fool for not recognising a missing
character-tuple " = 0" behind a function signature, as in:

struct IFoo { 
    virtual ~IFoo() {}
    virtual void frob (); // <-- missing pure specifier
}; 
struct Foo : IFoo { virtual void frob () {} }; 
int main () {
    IFoo *f = new Foo();
    f->frob();
    delete f;
}


The exact error message was

  "undefined reference to `vtable for IFoo'"

As this costed me a not irrelevant amount of time, and I wouldn't describe me
as unexperienced, my proposal would be to add a suggestion in case of undefined
vtable, in the spirit of

  undefined reference to `vtable for IFoo'
  Suggestions:
   * Ensure that no (pure) member function of `IFoo' became unintentionally
non-pure because of a missing or deleted `= 0'
   * Ensure that all non-pure member functions are defined *and* linked

Of course there exist more reasons for such vtable errors, but I think it can
already improve productivity to just enumerate the most common mistakes. 

Of course I learned my lesson for now, but probably I'll forget it again in
some months, and then, "undefined reference to `vtable for IFoo'" alone will
again not be of much help, as described in the introduction to this report.


-- 
           Summary: Add suggestion to "undefined reference to `vtable for
                    ...´"
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: phresnel at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44841