Mail Archives: cygwin-developers/1998/03/27/10:29:55
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The only size effect in declaring a destructor as virtual is that it
lengthens an objects vtable by sizeof(void*), admittedly 4-bytes is
not an issue. However, in a class that has no virtual functions it
also adds a vtable to the class and a vtable pointer to all of the
objects of that class. This increases the size of the objects by
sizeof(void*). This is only becomes a memory issue for small classes
that have a large number of instances.
By all means if a class has subclasses that contain explicitly
declared destructors, the superclass should have a virtual destructor.
See my previous message for more information on the need of virtual
destructors.
-----Original Message-----
From: Larry Hall [mailto:lhall AT rfk DOT com]
Sent: Wednesday, March 25, 1998 8:04 AM
To: Geoffrey Noer; cygwin32-developers AT cygnus DOT com
Cc: noer AT cygnus DOT com
Subject: Re: Mark ~fhandler_base virtual?
At 06:39 PM 3/24/98 -0800, Geoffrey Noer wrote:
>I've been cleaning up warnings generated by compiling cygwin32 with
>-Wall. One of them is that fhandler.h declares virtual functions
but
>has a non-virtual destructor.
>
>Should I make ~fhandler_base virtual? I *think* it's not necessary
>but wouldn't hurt either. The function set_name (which is the only
>thing that calls new and thus needs the destructor) is only called
by
>fhandler_base functions.
>
>--
>Geoffrey Noer
>noer AT cygnus DOT com
>
I haven't looked at fhandler_base but assuming its name is indicative
of
its function and the fact that there are virtual functions on this
class,
a virtual destructor is recommended. In general, if a class is a base
class, its destructor should be virtual. Also, there is no harm in
making
a destructor virtual even if the class is not a base class (or isn't
"yet").
Larry Hall lhall AT rfk DOT com
RFK Partners, Inc. (781) 239-1053
8 Grove Street (781) 239-1655 - FAX
Wellesley, MA 02181 http://www.rfk.com
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