[ros-dev] [ros-diffs] [greatlrd] 22195: make malloc, calloc and some other function return NULL if size is 0

[Magnus Olsen]

HI
Malloc(0) did not reaturn NULL;
that was the fix for. I am reading the IEEE spec
how malloc should work, and it exists two diffent
implement of it. and some exprenet on diffent windows
platfrom show diffent behvior about malloc(0)


----- Original Message ----- 
From: "Gunnar Dalsnes" <hardon at online.no>
To: "ReactOS Development List" <ros-dev at reactos.org>
Sent: Saturday, June 03, 2006 6:16 PM
Subject: Re: [ros-dev] [ros-diffs] [greatlrd] 22195: make malloc,calloc and
some other function return NULL if size is 0


> Was the changes made to fix something? If not: don't fix whats not broken.
>
> MSDN: The return value is NULL if the size is zero and the buffer
> argument is not NULL, or if there is not enough available memory to
> expand the block to the given size. In the first case, the original
> block is freed. In the second, the original block is unchanged.
>
> Magnus Olsen wrote:
> > Maybe we should add free to realloc and expand
> > to avoid memmory leak ??
>
> NO!!!!!!!!!!!!! MSDN says the memory will not be freed if the call
> fails, so the caller is free to continue to use the memory for whatever
> he likes.
>
> >
> > I know realloc fail in windows it can create memory leak
>
> MSDN: The return value is NULL if the size is zero and the buffer
> argument is not NULL, or if there is not enough available memory to
> expand the block to the given size. In the first case, the original
> block is freed. In the second, the original block is unchanged.
>
> So, if realloc fails in windows it WILL ALWAYS create a memory leak
> (unless you free the memory urself offcourse:-)
>
> >
> > text from internet how malloc should work
>
> With Internet do you mean MSDN? Every implementation of malloc behave
> different. We only want it to behave like the Windows version...
>
> >
> > " If the size of the space requested is 0, the behavior is
> > implementation-defined:
> >   the value returned shall be either a null pointer or a unique
pointer."
> >
>
> MSDN: If size is 0, malloc allocates a zero-length item in the heap and
> returns a valid pointer to that item.
>
> >
> > But most devloper assume malloc will return NULL if size is 0
> >  But some windows platfroms it return vaild pointer.
> >
> > The question is how should we handle it in reactos,
> > return NULL or vaild pointer  for this case ?
> >
>
> Don't try to be smart, just do it like it says on MSDN.
>
> BTW: The original code looks correct to me.
>
> >
> >
> > ----- Original Message ----- 
> > From: "Thomas Weidenmueller" <w3seek at reactos.com>
> > To: "ReactOS Development List" <ros-dev at reactos.org>
> > Sent: Saturday, June 03, 2006 4:39 PM
> > Subject: Re: [ros-dev] [ros-diffs] [greatlrd] 22195: make malloc, calloc
and
> > some other function return NULL if size is 0
> >
> >
> >> Royce Mitchell III wrote:
> >>>> @@ -60,6 +66,9 @@
> >>>>  */
> >>>> void* realloc(void* _ptr, size_t _size)
> >>>> {
> >>>> +   if ( _size == 0)
> >>>> +       return NULL;
> >>>> +
> >>>>    if (!_ptr) return malloc(_size);
> >>>>    if (_size) return HeapReAlloc(hHeap, 0, _ptr, ROUND_SIZE(_size));
> >>>>    free(_ptr);
> >>>> @@ -71,6 +80,9 @@
> >>>>  */
> >>>>
> >>>>
> >>> umm... shouldn't we call free() if we're going to return NULL because
> >>> size is 0?
> >> realloc never frees the memory if it fails.
> >>
> >>> Also, the free() at the bottom is never called now.
> >> it's wrong and shouldn't even be there ;)
> >>
> >>>> void* _expand(void* _ptr, size_t _size)
> >>>> {
> >>>> +   if ( _size == 0)
> >>>> +       return NULL;
> >>>> +
> >>>>    return HeapReAlloc(hHeap, HEAP_REALLOC_IN_PLACE_ONLY, _ptr,
> > ROUND_SIZE(_size));
> >>>> }
> >>>>
> >>>>
> >>> Again, shouldn't we free the existing buffer if we're returning NULL
> >>> because size is 0?
> >> no, same as with realloc.
> >>
> >> - Thomas
> >> _______________________________________________
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> >
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> >
> >
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