Re: Serializing binary data for use accross different platforms
On 5 May, 20:36, "Peter Olcott" <NoS...@OCR4Screen.com> wrote:
"James Kanze" <james.ka...@gmail.com> wrote in message
news:e311c699-c55c-466e-9041-41f16d97ba2b@s29g2000yqd.googlegroups.com...
On May 5, 7:51 pm, Victor Bazarov
<v.baza...@comcast.invalid> wrote:
On 5/5/2010 2:40 PM, Peter Olcott wrote:
If only integer base types are used, then it seems that
serializing data for cross platform use requires only two
things:
(1) Decomposing aggregate types into sequences of
integral types.
(2) Accounting for Endianess (Big, Little, Mixed).
Endianess can be determined at run time by casting known
values (such as 0x12345678, and 0x1234) for unsigned int
and unsigned short into char*.
Is there anything that I am missing here?
Uh... Only the possible problems with different
representations of negative values (one's complement vs
two's complement vs signed magnitude).
And the fact that the number of bits in a char can vary, and
that the size isn't always 2,4,8... And that there can be
bits
I think that this may be rare enough to ignore.
It depends on your requirements. You specifically asked about
cross platform stuff. For many applications, they are rare
enough to ignore. For many applications, everything but PC's
are "rare enough to ignore"; for many others, PC's and a few
mainstream Unix (Linux on PC, Solaris on Sparc, etc.) will
suffice. For others, IBM mainframes must be considered (with
non IEEE floating point and EBCDIC characters). And at least
one commercial mainframe today uses 48 bit sign-magnitude ints,
and another 36 bit 1's complement.
which don't contribute to the representation, but must have
some particular value. And that even for a 4 byte 2's
complement, there are quite a few different orderings
possible: I've seen at least three on popular machines.
Are you talking about byte orderings, Endianess?
Byte order. There are 24 different ways to order 4 bytes. In
practice, I've only seen three. But treating such ints as
values always works, regardless of the representation and byte
order.
--
James Kanze