From: dizzy (dizzy_at_[hidden])
Date: 2008-05-23 07:46:54
On Friday 23 May 2008 14:05:56 Roland Schwarz wrote:
> Neil Mayhew wrote:
> > This code is still in the vault, but I'd like to see it in the main part
> > of boost. What needs to be done to make this happen?
> >
> > The endian library is exactly what I've been looking for, and I would
> > really like to use it in my work, but I can't justify that to my
> > colleagues if it's not an official part of boost.
>
> This is an interesting library indeed! Thank you for having this
> brought up on the list again.
>
> However I have some concerns about usefulness when it comes to
> compiler independence and platform independence.
>
> One of the goals of such a library to be useful (for me at least) would
> be to be able to create compiler/platform independent binary files.
>
> I can see two problems here:
>
> 1) struct layout.
> The standard gives no provisions for struct layout. So e.g. for
>
> struct foo {
> big8_t a;
> big32_t b;
> };
>
> one cannot predict the alignment of the members. (Or am I wrong
> in this respect?)
Correct, which is why protocol binary structures are never mapped directly in
memory (you can with some compiler extensions but you won't gain anything
since I/O is the bottleneck in such cases and not memory copy). Instead a
serialization aproach should solve such issues.
> 2) The standard makes no provision for object representation, so
> writing out a bit pattern (which essentially is object
> representation) cannot be guaranteed to be read in on another
> platform. (Irresepective of endianess.) The only way to do
> this is to map object values to a stream of chars.
> One way to implement this mapping is to convert to ASCII
> representation (this is what the standard lib provides), but
> as I believe this is not the only mapping possible.
> I can imagine a mapping to char values that is less computing
> intensive and will resemble binary a little closer.
>
> In an attempt to solve issue 1) I came up with something like:
>
> struct foo
> {
> foo(char* begin, char* end)
>
> : x(begin)
>
> , y(begin)
> , z(begin)
> {}
>
> field<int, bigint32_t, 0> x;
> field<short int, bigint16_t, 32> y;
> field<short int, bigint16_t, 48> z;
> };
That kinda looks like reinventing boost.serialization although with a
different API (I did something similar in my code).
I'm not sure if boost.serialization allows read/write on different platforms
right now, if not, something could be added to it to do so (a new kind of
archive type maybe).
-- Mihai RUSU Email: dizzy_at_[hidden] "Linux is obsolete" -- AST