Help: C++ virtual tables not created

Help: C++ virtual tables not created

[Klaus Kaempf]

This one really bugs me. EGCS (and gcc 2.8.0) on openVMS/Alpha fail
to generate virtual tables in the assembler output. When checking iostream.obj
from libio with 'nm --demangle', I get:
                 U istream::ios virtual table
                 U ostream::ios virtual table
                 U iostream::ios virtual table

However, if I compile a sunos-pre(!)compiled version of iostream.cc on
openVMS, I get:
0000000000009638 D istream::ios virtual table
0000000000009648 D ostream::ios virtual table
0000000000009628 D iostream::ios virtual table

So to me, this looks like a bug in cpp and not in cc1plus ?!
Question is, what makes the c++-compiler generate virtual tables. I can't
get a clue from 'diff'ing the preprocessor outputs.

Klaus
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Re: Help: C++ virtual tables not created

[Martin von Loewis]

> So to me, this looks like a bug in cpp and not in cc1plus ?!

Quite unlikely. More likely, you are getting the wrong header files
on openVMS.

> Question is, what makes the c++-compiler generate virtual tables. I can't
> get a clue from 'diff'ing the preprocessor outputs.

AFAIK, g++ looks for some attributes of the class, and implements the
VT in the file which also has the attribute. A possible list is:
- first virtual function is implemented here
- first static member data is implemented here
- first non-inline constructor is implemented here
or the like. These are not the actual criteria used by g++, but you
get the idea.

Regards,
Martin