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From: sakkinen@tukki.jyu.fi (Markku Sakkinen)
Newsgroups: comp.lang.c++
Subject: Re: Change to delete is in order
Message-ID: <3743@tukki.jyu.fi>
Date: 14 Mar 90 07:54:54 GMT
References: <5136@odin.SGI.COM> <25FC0210.26173@paris.ics.uci.edu>
Reply-To: sakkinen@jytko.jyu.fi (Markku Sakkinen)
Organization: University of Jyvaskyla, Finland
Lines: 37

In article <25FC0210.26173@paris.ics.uci.edu> rfg@ics.uci.edu (Ronald Guilmette) writes:
>In article <5136@odin.SGI.COM> shap@delrey.sgi.com (Jonathan Shapiro) writes:
>>I believe that a small change to the definition of the delete operator
>>is worth considering.  The change would have no effect on correct
>>programs, but would help find incorrect programs in some circumstances.
>>
>>	delete should be defined to zero the pointer it is handed
>>	after freeing the associated store.
>
>That would be a swell idea, except that I don't believe that the value
>in a delete statement is required to be an lvalue.  What should the compiler
>do if the value is *not* an lvalue?  Punt?

Right: If the delete operator is redefined for a class, then according
to the C++ 2.0 Reference Manual it will be like
   void operator delete (void*)
(possibly with a second argument). Thus it only gets a _copy_ of the
pointer value.

Shapiro's proposal is nevertheless sensible, and would make 'new' and
'delete' more symmetric. The zeroing could be done _if_ the operand
is an lvalue. For a redefined delete operator, this could be done
_before_ it is actually invoked, but after the destructor (if any)
is invoked.

Of course one can keep many pointers to a dynamic object,
but in the majority of cases in "typical" code there is probably
only one pointer to each object, and so zeroing it automatically
would help a lot, e.g. prevent trivial errors.

Markku Sakkinen
Department of Computer Science
University of Jyvaskyla (a's with umlauts)
Seminaarinkatu 15
SF-40100 Jyvaskyla (umlauts again)
Finland
          SAKKINEN@FINJYU.bitnet (alternative network address)