endianess question

I want to write a unix socket program for two different machine
architectures(Sparc & x86). I know that Internet protocols follow big
endian architecture. Hence when do a send() from x86 architecture will
send() implicilty convert buffer into big endian or I have to do htonl()
explicitly before doing a send ?

Tejas Kokje
University of Southern California

Tejas Arun Kokje wrote:
> I want to write a unix socket program for two different machine
> architectures(Sparc & x86). I know that Internet protocols follow big
> endian architecture. Hence when do a send() from x86 architecture will
> send() implicilty convert buffer into big endian or I have to do htonl()
> explicitly before doing a send ?

IP packets use big endian order. A socket just sends bytes and knows nothing
about what type of data is actually being sent.

It is up to you to decide whether to use big or little endian order in your
messages, and convert when needed. I would decide if most of your machines will
be big or little endian, and then choose the most used one so that most machines
will not need to convert the data.

> Tejas Kokje
> University of Southern California

--
Phil Frisbie, Jr.
Hawk Software
http://www.hawksoft.com

On Thu, 09 Sep 2004 15:34:04 +0000, Tejas Arun Kokje wrote:

>
> I want to write a unix socket program for two different machine
> architectures(Sparc & x86). I know that Internet protocols follow big
> endian architecture. Hence when do a send() from x86 architecture will
> send() implicilty convert buffer into big endian or I have to do htonl()
> explicitly before doing a send ?
>
> Tejas Kokje
> University of Southern California

If you always do hton__ and ntoh__, you will have no problems, and your
code will be portable.

"Phil Frisbie, Jr." <(E-Mail Removed)> wrote in message
news:x750d.12919$(E-Mail Removed)...
> Tejas Arun Kokje wrote:
> > I want to write a unix socket program for two different machine
> > architectures(Sparc & x86). I know that Internet protocols follow big
> > endian architecture. Hence when do a send() from x86 architecture will
> > send() implicilty convert buffer into big endian or I have to do htonl()
> > explicitly before doing a send ?
>
> IP packets use big endian order. A socket just sends bytes and knows
nothing
> about what type of data is actually being sent.
>
> It is up to you to decide whether to use big or little endian order in
your
> messages, and convert when needed. I would decide if most of your machines
will
> be big or little endian, and then choose the most used one so that most
machines
> will not need to convert the data.

There are some really good books on TCP/IP programming that will walk you
through it. Search for things like hton and ntoh

Tejas Arun Kokje <(E-Mail Removed)> writes:

> I want to write a unix socket program for two different machine
> architectures(Sparc & x86). I know that Internet protocols follow big
> endian architecture. Hence when do a send() from x86 architecture will
> send() implicilty convert buffer into big endian or I have to do htonl()
> explicitly before doing a send ?

send does not convert anything. How could it? It doesn't know what
kind of data you're sending!

Always use htonl and ntohl explicitely on _binary_ _data_.

Of course, you could rather use an ASCII protocol:

- since you have to convert with htonl or ntohl, converting to and
from ascii (printf and scanf) won't seem harder.

- you will be able to connect and try your server and client code
with telnet.

- you will be able to see what's going "on the wire" with tcpdump
or other tools with no need of decrypting hex dumps.

- you could end with less data to be transmited! For example,
geographic data (which consists mainly of numbers) is quite
smaller when expressed in ASCII than when put in binary.



--
__Pascal Bourguignon__ http://www.informatimago.com/

Our enemies are innovative and resourceful, and so are we. They never
stop thinking about new ways to harm our country and our people, and
neither do we.