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
STANDARDS
The htonl(),
htons(), ntohl(), and
ntohs() functions conform to IEEE
Std 1003.1 (“POSIX.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, amd64, i386, and some mips and arm architectures, bytes are handled backwards from most everyone else in the world. This is not expected to be fixed in the near future.