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 -- Mihai RUSU Email: dizzy@roedu.net "Linux is obsolete" -- AST