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From: tuck@jason.cs.unc.edu (Russ Tuck)
Newsgroups: comp.lang.c++
Subject: virt base c'tor -- my error or CC bug?
Keywords: CC, cfront, 2.0, multiple inheritance, virtual base class
Message-ID: <11582@thorin.cs.unc.edu>
Date: 22 Jan 90 17:41:10 GMT
Sender: news@thorin.cs.unc.edu
Reply-To: tuck@jason.cs.unc.edu (Russ Tuck)
Distribution: na
Organization: University Of North Carolina, Chapel Hill
Lines: 38

I think I've found a bug in the AT&T C++ 2.0 compiler, cfront, but I'm 
willing to be shown the error in my code.  On p. 82, section 12.6.2, of
the C++ (2.0) Reference Manual (AT&T select code 307-146), it says:
"All sub-objects for virtual base classes are initialized by the constructor
of the most derived class.  If a constructor of the most derived class
does not specify a mem-initializer for a virtual base class then that
virtual base class must have a default constructor or no constructors."

The example in the manual following the quote above shows the case of
no mem-initializer in the most derived class's constructor, where the
virtual base class has a default constructor.  I would like to use the
other case described in the quote: a mem-initializer in the most derived
class's constructor and no default initializer in the virtual base class.
Here's a trivial example program showing this case.

  class V { public: V(int); };

  class A : public virtual V { public: A(); };

  A::A() : V(1) {}

  V v(1);
  A a;

CC (cfront 2.0, running on any of Sun4, DEC 3100, VAX 785) gives these 
error messages when compiling the above code:

CC  t.c:
"t.c", line 3: error: virtual base V has no default initializer
"t.c", line 5: error: unexpected argument list: no base class V 
2 errors

Is there something wrong with this code, or is this indeed a compiler bug?

Russ Tuck		               tuck@cs.unc.edu
UNC Dept. of Computer Science          ...!mcnc!unc!tuck
CB 3175, Sitterson Hall
Chapel Hill, NC 27599-3175, USA        (919) 962-1755 or 962-1700