Re: malloc/free & new/delete balance

[mrs at wrs dot com (Mike Stump)]

> To: Carlo Wood <carlo@runaway.xs4all.nl>
> Cc: egcs@cygnus.com (egcs@cygnus.com)
> From: Alexandre Oliva <oliva@dcc.unicamp.br>
> Date: 29 Jun 1998 21:54:36 -0300

> > This unbalance between calling `::operator new(size_t)' and
> > `free(void *)' is causing troubles when `operator new(size_t)' and
> > `operator delete(void *)' are overloaded

> Agreed, but, for some reason, the FDIS [lib.new.delete.array]
> defines operator new[](size_t) as returning operator new(size_t) by
> default, while it states that operator delete[](void*) frees

Can you provide an exact quote of this?  I can't find it.  I'll quote
from the FDIS below.

> the pointer it is given.  So, I'd say the implementation is correct,
> and calling operator delete(void*) is non-standard.  Too bad. :-(

The next stage of your learning is to be able to say when the standard
is wrong.  :-)

Also, I think we are staring at different papers.  Does yours have the
number 14882 or X3J16/97-0079 on it?  If not, that isn't the FDIS, and
you should not call it that.

>From the real FDIS:

void operator delete[](void* ptr) throw();
void operator delete[](void* ptr, const std::nothrow_t&) throw();

-9- Effects: The deallocation function
 (basic.stc.dynamic.deallocation) called by the array form of a
 delete-expression to render the value of ptr invalid.

-10- Replaceable: a C++ program can define a function with this
 function signature that displaces the default version defined by the
 C++ Standard library.

-11- Required behavior: accept a value of ptr that is null or that was
returned by an earlier call to operator new[](std::size_t) or operator
new[](std::size_t,const std::nothrow_t&).

-12- Default behavior: 

       For a null value of ptr , does nothing. 

       Any other value of ptr shall be a value returned earlier by a
       call to the default operator new[](std::size_t).*

              [Footnote: The value must not have been invalidated by
              an intervening call to operator delete[](void*)
              (lib.res.on.arguments). --- end foonote]

       For such a non-null value of ptr , reclaims storage allocated
       by the earlier call to the default operator new[].

-13- It is unspecified under what conditions part or all of such
reclaimed storage is allocated by a subsequent call to operator new or
any of calloc, malloc, or realloc, declared in <cstdlib>.


Note the word above, ``reclaims.''  The calls should be symmetric as
one would guess without reading the standard.  In fact, it is a bug
that the standard doesn't refine the language and say exactly that it
must call delete.