Re: [boost] [serialization] patch for portable_binary_oarchive.hpp

From: David Abrahams (dave_at_[hidden])
Date: 2007-11-02 16:33:45

on Fri Nov 02 2007, "Boris Gubenko" <Boris.Gubenko-AT-hp.com> wrote:

> Two serialization library tests: test_demo_portable_archive[_dll] fail
> to compile on many platforms with invalid type conversion error. I did
> not check all the platforms, but I'd expect it to fail on any big endian
> platform. 

I can't imagine how your change would fix an endianness problem.
Also, your change relies on the nonportable (implementation-defined)
behavior of reinterpret_cast.

I think the correct change to silence the type conversion error is

  char * first = static_cast<char *>(static_cast<void *>(const_cast<long*>(& l)));

However the code in itself invokes undefined behavior by modifying a
constant object (l).  The byte reversal needs to be done in a separate
buffer.

> The patch below fixes the problem, verified on HP-UX with
> both aC++ and gcc.
>
> Ok to commit?
>
> Index: example/portable_binary_oarchive.hpp
> ===================================================================
> --- example/portable_binary_oarchive.hpp        (revision 40687)
> +++ example/portable_binary_oarchive.hpp        (working copy)
> @@ -76,7 +76,7 @@
>
>          // we choose to use litle endian
>          #ifdef BOOST_BIG_ENDIAN
> -            char * first = static_cast<char *>(static_cast<void *>(& l));
> +            char * first = reinterpret_cast<char *>(const_cast<long *>(& l));
>              char * last = first + sizeof(l) - 1;
>              for(;first < last;++first, --last){
>                  char x = *last;
>
> Thanks,
>   Boris
>
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-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com