Re: [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(a)online.no>
To: "ReactOS Development List" <ros-dev(a)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(a)reactos.com>
>  > To: "ReactOS Development List" <ros-dev(a)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
> > >  _______________________________________________
> > >  Ros-dev mailing list
> > >  Ros-dev(a)reactos.org
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> >
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