Re: [boost] offset_cast proposal

From: Terje Slettebø (tslettebo_at_[hidden])
Date: 2002-11-24 07:26:05

>From: "Pavol Droba" <droba_at_[hidden]>

> I have developed a simple cast function which I found very useful. Here it
is:
>
> template< typename T >
> inline T offset_cast( void* p, unsigned int  offset=0 )
> {
> return reinterpret_cast< T >( static_cast<unsigned char*>( p )+offset );
> }
>
> template< typename T >
> inline T offset_cast( const void* p, unsigned int offset=0 )
> {
> return reinterpret_cast< T >( static_cast<const unsigned char*>(
p )+offset );
> }
>
> Its purposes is to simplify a mapping of C-like structure onto binary
data. Here is
> the example: Assume thath you have a network packet in raw format, and you
want
> to read IP-header information. You could do following:
>
> ip_header* ip=offset_cast<ip_header>( packet, ip_header_offset );
>
> instead of ugly pointer arithmetic.

Uhm, I think pointer arithmetic could be preferrable to casts, particularly
reinterpret_cast, as pointer arithmetic is at least not
implementation-dependent, unlike the reinterpret_cast.

Also, I find nothing ugly about pointer arithmetic - in fact, STL is based
on it, except that it's abstracted as "iterators". int array[10];
std::for_each(array,array+10,f) is pointer arithmetic. Do you find that
ugly, as well?

"Ugly" is typically more used for casts. Whether they are wrapped in a
function, like the above, or not. This because they circumvent the type
system. This is something pointer arithmetic doesn't do.

Regards,

Terje