NetNews Usenet Archive 1992 #19/NN_1992_19.iso/spool/comp/lang/cplus/13308

Internet Message Format | 1992-09-07 | 2.6 KB

Path: sparky!uunet!van-bc!rsoft!agate!stanford.edu!ames!sun-barr!cs.utexas.edu!ut-emx!jamshid
From: [e-mail] (Jamshid Afshar)
Newsgroups: comp.lang.c++
Subject: Re: Explicit Calls to Destructors (SunCC=ok, gcc=not)
Summary: use "this->~T()" ("this->T::~T() to workaround gcc bug)
Keywords: destructors
Message-ID: <[e-mail]>
Date: 4 Sep 92 19:31:23 GMT
References: <[e-mail]>
Reply-To: [e-mail]
Organization: The University of Texas at Austin; Austin, Texas
Lines: 61

In article <[e-mail]> [e-mail] (Darrell Schiebel) writes:
>    In the Sun (SC1.0 w/ cfront 2.1 (I think)), an explicit call
>    to a class' destructor from within a one of the class' member
>    functions works:
>
>    void Tess::cleanup(Bool abort) {
>      Tess::~Tess();
>        }

That's not the correct way to call a dtor.  It probably doesn't work
under later versions of cfront.

>    However, in gcc-2.2.2 this does not work ...
>
>    Other nonworking variations:
>
>    this->~Tess();            AND
>    (*this).~Tess();        WITH THE ERROR MESSAGE: ...

Both of these are correct -- you've encountered a gcc-2.2.2 bug.
Btw, it is also legal (since the ARM) to explicitly destroy built-in
types (it's a no-op, of course).  This makes it easier to instantiate
templates which explicitly destroy their objects with built-in types.
Note, BC++ 3.0 didn't implement this feature, and BC++ 3.1 only allows
one form of the syntax:

    int i;
    int* p = &i;
    i.~int();  // correct, but BC++ error
    p->~int();  // correct, but BC++ error
    i.int::~int();  // correct, but BC++ error
    p->int::~int();  // correct and BC++ allows

The difference between:
    p->~T();
and
    p->T::~T();
is that the second overrides the "virtualness" of the dtor (if it is
virtual).  You should therefore almost always use the first form.  Besides,
it's less characters and not any slower if ~T() isn't virtual.

>    and finally:
>
>    ~Tess();            WITH:

You must explicitly use a "." or "->" whenever calling the dtor, even
from within a member function.  'this' is not assumed.  The above
tries to create a temporary Tess and call it's unary ~ operator (see
ARM 12.4).

>    Is there some way to get around this in gcc? Its exactly what
>    I want to do; I don't want to force users of my class to call
>    parent ``cleanup'' functions, in children. Explicit calls to
>    destructors is permitted, ARM p.278, sec 12.4.

I think someone said "this->Tess::~Tess()" works under gcc.  Just
remember that this will not call the destructor of derived class
(I'm assuming ~Tess() is declared virtual).

Jamshid Afshar
[e-mail]