Re: Encoding of primitives for binary serialization
Tom Anderson wrote:
On Thu, 9 Apr 2009, kb wrote:
I'm implementing binary serialization for primitive data types both in
java and c++. Also I need to handle serialization/de-serialization
across java and c++ i.e. serialization from java and de-serialization
in c++ and vice-versa.
For this I need to decide an encoding for primitive data types which
is independent of language and platform. Does any one have some idea
about such an encoding format.
Use the formats used in internet protocols - see pretty much any
low-level RFC for details. The TCP and IP ones would do. Bytes are
bytes, 16- and 32-bit numbers are written out byte by byte in 'network
byte order', ie most significant first. In java, use
Data{Out,In}putStream for that, and in C, the htons/ntohs and
htonl/ntohl functions from arpa/inet.h. Not sure what you do about
64-bit numbers. You can do signed and unsigned, but be aware that in
java, which has no native unsigned types, you'll need to use the next
bigger type to hold unsigneds, eg an unsigned short will need an int to
hold.
It is not that hard to code htonll and ntphll (or whatever one will call
them) if 64 bit integers (long long's) are available - and these
functions would probably not be needed if they were not.
Floating-point numbers are harder; you might be better off avoiding them
altogether if possible, but if not, use the IEEE 754 32- and 64-bit
formats. Again, in java the Data*putStreams do that. I'm not aware of
standard functions to do it in C, though - if you're on a machine which
uses 754 natively, you can just pun the float as an int and write that
out (through the htonl function, i think). On one that doesn't, like an
x86, you'll need to find a machine-specific library with an encoding
function in it.
x86 uses IEEE floating point.
Most real computers do today. Old IBM mainframes and DEC VAX'es did not.
Alternatively, relax the 'binary' requirement and use JSON.
Or XML.
Arne