Re: 20000927: CPP Friend problem on IBM AIX

Hi Dan,

You asked:

> I found the CPP workaround for the friend problem.  Did anyone from
> your organization report the problem to IBM?

I assume you're referring to workarounds in the the answer to Harsh Passi 
appended to this message.

No one here reported the problem to IBM, because we didn't know who to 
report it to, but we probably should have looked harder.  Please feel
free to report this bug if you know who to tell to get it fixed.  I
didn't feel confident enough of my waning C++ knowledge (mostly replaced by
Java) to make a convincing argument that the AIX compiler behaviour
violates the standard ...

--Russ

-----------------------------------
<Answer>
>From: Harsh Anand <address@hidden>
>Subject: netcdf 3.5-beta3 installation problem on IBM SP
>Organization: LBNL/NERSC
>Keywords: 200008022147.e72LljT08254 netCDF 3.5-beta3

Hi Harsh,

> I got  errors like
> 
>        xlC -c  -I../libsrc -I.  -DNDEBUG netcdf.cpp
> "netcdfcpp.h", line 156.10: 1540-0133 (S) The attributes "friend" are
> not allowed.
> 
> installing C++ interface on the IBM SP3  we have at NERSC Lawrence
> Berkeley Lab:
> 
>  FYI  -- IBM tech support folks tell me that  it is not a bug. According
> to the
> standard   "The attributes "friend" are not allowed".    Could you
> please suggest any workaround for this problem?
> I have successfully compiled this program using  KAI C++ compiler.

See a previous message for a workaround:

  http://www.unidata.ucar.edu/glimpse/netcdf/3814

But I don't understand how this could be non-standard C++.  The draft
standard available from

  http://www.cygnus.com/misc/wp/dec96pub/access.html includes the

following example:

 4 When a friend declaration refers to an overloaded  name  or  operator,
   only  the  function specified by the parameter types becomes a friend.
   A member function of a class X can be a friend of a class  Y.   [Exam-
   ple:
           class Y {
               friend char* X::foo(int);
               // ...
           };

which uses the same syntax we use.  Is it that you can't declare a
private constructor to be a friend?  If so, I haven't seen that
restriction explicitly stated anywhere.  Can you find out where in the
standard this syntax is disallowed, since no other C++ compiler we
have tried objects to it?

A less heavy-handed workaround would be to declare the whole NcFile
class to be a friend rather than just particular member functions,
that is use

  friend NcFile;

instead of

  friend NcFile::NcFile( const char *, FileMode, size_t*, size_t);
  friend NcBool NcFile::sync( void );
  friend NcDim* NcFile::add_dim( NcToken, long );
    // to delete dimensions, since destructor is private
  friend NcBool NcFile::close( void );

and similarly for other places where the compiler objects to the
declarations of particular member functions as friends.  But I don't
understand why this should be necessary ...
</Answer>

--Russ