Conference turris::c_plus_plus

3560.0. "%LINK-W-USEUNDEF when compiled /debug" by CSC32::V_HAVER () Fri May 02 1997 22:16

Following code compiles and links fine if you do:

$ cxx test
$ link test

class A {
private:
  static int m_nStatic;
};

int main() {
  return 0;
}

But it gets errors if you use /debug

$ cxx/deb/noopt test
$ link/deb test
%LINK-W-NUDFSYMS, 1 undefined symbol:
%LINK-I-UDFSYM,         M_NSTATIC__1A
%LINK-W-USEUNDEF, undefined symbol M_NSTATIC__1A referenced
        in debug or traceback record
        in module TEST file DKB500:[V_HAVER]TEST.OBJ;11

Using /deb without /noopt makes no difference.  Also tried /names=as_is, and
other combinations.

There are some related notes, but they seem to have to do with templates,
functions, name mangling, etc.  Sorry if this has been discussed before.

It's as if the reference is optimized away regardless, but the debug record
needs to see that it is defined.

Without using /debug it would be nice to know there are unreferenced
symbols.

Tested on DEC C++ V5.5-017, OpenVMS Alpha V7.0

    This has been logged as CXXC_BUGS 4335.
    
    For the time being, my suggestion is to define the static data member.
    Note that the linker gives warnings, not errors; the program will still
    run perfectly fine.  I'm still looking into this, and will write more
    later.

    It's not that it's optimized away, it's that you don't use that static
    data member anywhere.  If you were to change the program to the
    following, you would get link warnings regardless (but this program
    would not run correctly, as you actually use the data member):

    ---------------------                                         
    class A {
    public:
      static int m_nStatic;
    };

    int main() {
      return A::m_nStatic;
    }
    ---------------------

    Re warnings: We always used to put out linker warnings for undefined 
    static data members, but we were inundated with complaints from customers; 
    we don't warn anymore.

    							- Matt