Endian issues in TCP/IP Post: 16429

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Top Forums UNIX for Advanced & Expert Users Endian issues in TCP/IP Post 16429 by Perderabo on Friday 1st of March 2002 09:24:26 AM

03-01-2002

Administrator Emeritus

Your question is very confusing. I don't know if you are trying to port software or write a TCP/IP program.

Endian-ness is decided by the hardware not the the software. If an OS wants to use integer arithmetic, it must go along with what the hardware designers did. A very few cpu's are, um, bi-endian, but most have a preference.

HP hardware is big-endian.

TCP/IP does not even assume that computers have 8 bit bytes, which is why it calls 8 bits an "octet". 32 bit and 16 bit quantities travel over the network in big endian form. But portable programs access them via macros defined in the include file arpa/inet.h. The macros are ntohl, ntohs, htonl, htons. They stand for stuff like "network to host short". With big endian computers, these macros are null. But you should still use them. That way your code works on other computers. Only the macros need to be rewritten.

Perderabo

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LEARN ABOUT OSX

ntohs

BYTEORDER(3)						   BSD Library Functions Manual 					      BYTEORDER(3)

NAME

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

LIBRARY

     Standard C Library (libc, -lc)

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

     These routines convert 16 and 32 bit quantities between network byte order and host byte order.  (Network byte order is big endian, or most
     significant byte first.)  On machines which have a byte order which is the same as the network order, routines are defined as null macros.

     These routines are most often used in conjunction with Internet addresses and ports as returned by gethostbyname(3) and getservent(3).

SEE ALSO

     gethostbyname(3), getservent(3)

STANDARDS

     The byteorder functions are expected to conform with IEEE Std POSIX.1-200x (``POSIX.1'').

HISTORY

     The byteorder functions appeared in 4.2BSD.

BUGS

     On the VAX bytes are handled backwards from most everyone else in the world.  This is not expected to be fixed in the near future.

BSD
								   June 4, 1993 							       BSD