BYTEORDER(3) AerieBSD 1.0 Refernce Manual BYTEORDER(3)


htonlhtons, ntohl, ntohs, htobe64, htobe32, htobe16, betoh64, betoh32, betoh16, htole64, htole32, htole16, letoh64, letoh32, letoh16, swap64, swap32, swap16 convert values between different byte orderings


#include <sys/types.h>

u_int32_t htonl(u_int32_t host32);

u_int16_t htons(u_int16_t host16);

u_int32_t ntohl(u_int32_t net32);

u_int16_t ntohs(u_int16_t net16);

u_int64_t htobe64(u_int64_t host64);

u_int32_t htobe32(u_int32_t host32);

u_int16_t htobe16(u_int16_t host16);

u_int64_t betoh64(u_int64_t big64);

u_int32_t betoh32(u_int32_t big32);

u_int16_t betoh16(u_int16_t big16);

u_int64_t htole64(u_int64_t host64);

u_int32_t htole32(u_int32_t host32);

u_int16_t htole16(u_int16_t host16);

u_int64_t letoh64(u_int64_t little64);

u_int32_t letoh32(u_int32_t little32);

u_int16_t letoh16(u_int16_t little16);

u_int64_t swap64(u_int64_t val64);

u_int32_t swap32(u_int32_t val32);

u_int16_t swap16(u_int16_t val16);


These routines convert 16, 32 and 64-bit quantities between different byte orderings. The “swap” functions reverse the byte ordering of the given quantity; the others convert either from/to the native byte order used by the host to/from either little- or big-endian (a.k.a network) order.

Apart from the swap functions, the names can be described by this form: {src-order}to{dst-order}{size}. Both {src-order} and {dst-order} can take the following forms:

Host order.
Network order (big-endian).
Big-endian (most significant byte first).
Little-endian (least significant byte first).

One of the specified orderings must be ‘h’. {size} will take these forms:

Long (32-bit, used in conjunction with forms involving ‘n)’.
Short (16-bit, used in conjunction with forms involving ‘n)’.

The swap functions are of the form: swap{size}.

Names involving ‘n’ convert quantities between network byte order and host byte order. The last letter .Pf ( Sq s or ‘l’) is a mnemonic for the traditional names for such quantities, short and long, respectively. Today, the C concept of short and long integers need not coincide with this traditional misunderstanding. On machines which have a byte order which is the same as the network order, routines are defined as null macros.

The functions involving either “be”, “le”, or “swap” use the numbers 16, 32, or 64 for specifying the bitwidth of the quantities they operate on. Currently all supported architectures are either big- or little-endian so either the “be” or “le” variants are implemented as null macros.

The routines mentioned above which have either {src-order} or {dst-order} set to ‘n’ are most often used in conjunction with Internet addresses and ports as returned by gethostbyname(3) and getservent(3).


gethostbyname(3), getservent(3)


The htonl();, htons();, ntohl();, and ntohs(); functions conform to The other functions are extensions that should not be used when portability is required.


The byteorder functions appeared in 4.2BSD.


On the vax, alpha, i386, and some mips architectures, bytes are handled backwards from most everyone else in the world. This is not expected to be fixed in the near future.

AerieBSD 1.0 Reference Manual May 26 2009 BYTEORDER(3)