BYTEORDER(3)

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

SYNOPSIS
#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);

DESCRIPTION
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:

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

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

l   Long (32-bit, used in conjunction with forms involving ‘n’).
s   Short (16-bit, used in conjunction with forms involving ‘n’).
16  16-bit.
32  32-bit.
64  64-bit.

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 (‘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).

SEE ALSO
gethostbyname(3), getservent(3)

STANDARDS
The htonl(), htons(), ntohl(), and ntohs() functions conform to p1003.1. The other functions are extensions that should not be used when portability is required.

HISTORY
The byteorder functions appeared in 4.2BSD.

BUGS
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.