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Subject: H5Part development and discussion

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[H5part] Re: error handling in H5hut

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  • From: Achim Gsell <achim.gsell AT>
  • To: Mark Howison <MHowison AT>
  • Cc: h5part AT
  • Subject: [H5part] Re: error handling in H5hut
  • Date: Fri, 2 Jul 2010 09:02:24 +0200
  • List-archive: <>
  • List-id: H5Part development and discussion <>

On Jul 1, 2010, at 10:44 PM, Mark Howison wrote:

> Hmm, so I'm confused about how the (ptr_diff) cast will work... if
> h5priv_alloc returns
> return (void*)(H5_ERR);
> isn't the cast to void* going to convert -1 to some bogus non-negative
> value? Why would (ptr_diff) convert it back to -1?

May be (void*)((char*)NULL + H5_ERR) is more save. But (void*)(H5_ERR) should
be save on all two-complement systems.

The 32bit two-complement representation of -1 is 0xffffffff. This is a valid
value for a pointer, even it will never be used. So the cast of H5_ERR to
void* gives 0xffffffff, which is a valid pointer difference. ptrdiff_t is a
signed integral type, and as such can be casted to compatible fundamental
data types. So

(int64_t)(ptrdiff_t)(void*)(H5_ERR) =
(int64_t)(ptrdiff_t)(void*)(-1) =
(int64_t)(ptrdiff_t)(0xffffffff) =
(int64_t)(ptrdiff_t)(-1) =


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