endianess problem!!!!

[sandeepvignesh]

I have a small doubt regarding endianess. My system here is little endian and the board I am communicating with is big endian. Hence the data received by the board is not same as what I am sending. I have heard about htons and htonl,are they used only for IP address conversion or even for data? I just need to make sure that data should be matched both the sides,so can anybody please help me out!!!!Thanks in advance.......

[Rubberman]

The network-byte-order conversion functions are useful for any data that is in network byte order. You can use them on one end to convert the data to network-byte-order and on the other end to convert to the local representation. If you send the data directly, without conversion, then you will have to deal with the conversions yourself, just to be safe.

[sandeepvignesh]

That means i need to convert the data into big-endian before transmitting to board and then back to board's byte-order right?

[Rubberman]

If network-byte-order ( nbo ) is big-endian, then yes. It's been so long since I had to deal with that cruft that I forgot what order it is. The technique I mentioned is how you transmit data from one system to another when you don't know what the endian-ness of the receiving machine happens to be. Then sender encodes and the receiver decodes. If they are compatible with nbo, then that is a do-nothing operation with no performance hit since typically the htons/htonl calls are compiler macros. Of course, if you are sending data structures, you also have to accomodate structure padding issues which is why most protocols that deal with binary data have some means to marshal structural data in a way that can be unambiguously decoded at the receiving end.

[sandeepvignesh]

Thanks a lot.Will let you know if at all I face any kind of problem!!!!!

[nonemmaverick]

Hi San,
Did u face any kind of problem while implementing the above detail.I couldnt make out the exact procedural emphasis of the network-byte-order posted by rubberman.I have a query related to the same issue.My board is also facing the same problem.In case of latent information how will the encoder-decoder react?Even iam spending a lot of time on that.Please elucidate ur understanding on the whole scenario.
Thanks

[Rubberman]

Hi San,
Did u face any kind of problem while implementing the above detail.I couldnt make out the exact procedural emphasis of the network-byte-order posted by rubberman.I have a query related to the same issue.My board is also facing the same problem.In case of latent information how will the encoder-decoder react?Even iam spending a lot of time on that.Please elucidate ur understanding on the whole scenario.
Thanks

Whenever you send binary data between systems on a network, on the sending side you need to encode each component item into network byte order (NBO). On the receiving end, you need to decode from NBO to native representation. Doing so will assure you that the data is correct after accounting for endian-ness. IE, the integer 1234 on the sending side will still be 1234 on the receiving side. There are macros to help you do this. From the htonl man page:

BYTEORDER(3)               Linux Programmer’s Manual              BYTEORDER(3)

NAME
       htonl,  htons,  ntohl,  ntohs  - convert values between host and network byte
       order

SYNOPSIS
       #include <arpa/inet.h>

       uint32_t htonl(uint32_t hostlong);

       uint16_t htons(uint16_t hostshort);

       uint32_t ntohl(uint32_t netlong);

       uint16_t ntohs(uint16_t netshort);

DESCRIPTION
       The htonl() function converts the unsigned integer hostlong  from  host  byte
       order to network byte order.

       The  htons() function converts the unsigned short integer hostshort from host
       byte order to network byte order.

       The ntohl() function converts the unsigned integer netlong from network  byte
       order to host byte order.

       The  ntohs()  function converts the unsigned short integer netshort from net-
       work byte order to host byte order.

       On the i80x86 the host byte order is Least Significant  Byte  first,  whereas
       the  network  byte  order,  as used on the Internet, is Most Significant Byte
       first.

CONFORMING TO
       POSIX.1-2001.

       Some  systems  require   the   inclusion   of   <netinet/in.h>   instead   of
       <arpa/inet.h>.

SEE ALSO
       gethostbyname(3), getservent(3)

BSD                               1993-04-15                      BYTEORDER(3)

[nonemmaverick]

hi rubberman,
thanks a lot.that really helped.

[sandeepvignesh]

was about to reply to your Q,but i hope what rubberman xplained will do rite????