🚀 go-pugleaf

In article <xsod973w4m5.fsf@glob.cs.rpi.edu> vandevod@cs.rpi.edu
(David Vandevoorde) writes:

|> >>>>> "KK" == Kerry Kimbrough <kk@onr.com> writes:
|> KK> Joe Buck wrote:
|> KK>>  You can, of course, call the C realloc().

|> KK> But then crash? My understanding is that mixture of alloc/free and
|> KK> friends with new/delete is not guaranteed to be valid and
|> KK> therefore is discouraged.  Not true?
|> [...]

|> Since you can provide your own new operators etc., you can ensure that
|> it's safe to use realloc with new/delete (or you can provide a function
|> based on realloc with similar functionality).

I don't think you can make it safe even providing your own operator
new/delete (or rather operator new[]/delete[], since realloc only
makes sense on arrays).  There are two problems:

1. It is, in fact, impossible to obtain the address actually returned
by operator new[].  The implementation is allowed to (and most do) ask
for extra memory in order to maintain the number of elements.
Typically, this memory will be in front of the first element, so the
compiler will `fix up' the address returned by operator new[] before
you ever see it.

2. The implementation is allowed to save this address in some sort of
cache.  For example, an alternate implementation of a new expression
for an array would be for the implementation to maintain an
associative array of addresses to counts.

--
James Kanze         Tel.: (+33) 88 14 49 00        email: kanze@gabi-soft.fr
GABI Software, Sarl., 8 rue des Francs-Bourgeois, F-67000 Strasbourg, France
Conseils, études et réalisations en logiciel orienté objet --
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