Re: Overloading operator delete problem

From:
"Greg Herlihy" <greghe@pacbell.net>
Newsgroups:
comp.lang.c++.moderated
Date:
28 Aug 2006 08:29:33 -0400
Message-ID:
<1156739751.269002.182580@74g2000cwt.googlegroups.com>
albrecht.fritzsche wrote:

Hi,

I've overloaded operator new and operator delete like in the appended
code but don't know how to trigger a call to the nothrow-delete.

....

At least on Vis C++ the appended code compiles but uses for the last
delete the throwing-delete version. How do I have to specify the
std::nothrow? Where is this actually documented in the standard?

And, why do I get a strange error from Comeau (online) with exactly
this code saying

"ComeauTest.c", line 6: error: exception specification is incompatible with that of
          previous function "operator delete(void *)" (declared at line 67 of
          "new.stdh"):
            previously specified: no exceptions will be thrown
  void operator delete(void* memory) throw(std::bad_alloc) {


#include <new>
#include <cstdlib>

....

void operator delete(void* memory) throw(std::bad_alloc) {
     free(memory);
}


This declaration of delete() is incorrect. After all, how could delete
have a problem allocating memory when all that the function does is to
free memory? Furthermore, since throwing exceptions while destructing
objects is usually fatal to a program, it turns out that neither the
nothrow or non-nothrow delete() throws exceptions:

     void operator delete(void* memory) throw() {
           free(memory);
     }

Of course one may well wonder why a nothrow version of delete() exists
at all - since its behavior seems to be indistinguishable from the
non-nothrow version.

Greg

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