endian(3)

NAME#

htobe16, htole16, be16toh, le16toh, htobe32, htole32, be32toh, le32toh, htobe64, htole64, be64toh, le64toh - convert values between host and big-/little-endian byte order

LIBRARY#

Standard C library (libc, -lc)

SYNOPSIS#

#include <endian.h>

uint16_t htobe16(uint16_t \nhost_16bits\n);\n
\nuint16_t htole16(uint16_t \nhost_16bits\n);\n
\nuint16_t be16toh(uint16_t \nbig_endian_16bits\n);\n
\nuint16_t le16toh(uint16_t \nlittle_endian_16bits\n);

uint32_t htobe32(uint32_t \nhost_32bits\n);\n
\nuint32_t htole32(uint32_t \nhost_32bits\n);\n
\nuint32_t be32toh(uint32_t \nbig_endian_32bits\n);\n
\nuint32_t le32toh(uint32_t \nlittle_endian_32bits\n);

uint64_t htobe64(uint64_t \nhost_64bits\n);\n
\nuint64_t htole64(uint64_t \nhost_64bits\n);\n
\nuint64_t be64toh(uint64_t \nbig_endian_64bits\n);\n
\nuint64_t le64toh(uint64_t \nlittle_endian_64bits\n);

htobe16(), htole16(), be16toh(), le16toh(), htobe32(), htole32(), be32toh(), le32toh(), htobe64(), htole64(), be64toh(), le64toh():

\n
    Since glibc 2.19:
\n
        _DEFAULT_SOURCE
\n
    In glibc up to and including 2.19:
\n
        _BSD_SOURCE

DESCRIPTION#

These functions convert the byte encoding of integer values from the byte order that the current CPU (the "host") uses, to and from little-endian and big-endian byte order.

The number, nn, in the name of each function indicates the size of integer handled by the function, either 16, 32, or 64 bits.

The functions with names of the form "htobenn" convert from host byte order to big-endian order.

The functions with names of the form "htolenn" convert from host byte order to little-endian order.

The functions with names of the form "benntoh" convert from big-endian order to host byte order.

The functions with names of the form "lenntoh" convert from little-endian order to host byte order.

VERSIONS#

Similar functions are present on the BSDs, where the required header file is <sys/endian.h> instead of <endian.h>. Unfortunately, NetBSD, FreeBSD, and glibc haven't followed the original OpenBSD naming convention for these functions, whereby the nn component always appears at the end of the function name (thus, for example, in NetBSD, FreeBSD, and glibc, the equivalent of OpenBSDs "betoh32" is "be32toh").

STANDARDS#

None.

HISTORY#

glibc 2.9.

These functions are similar to the older byteorder(3) family of functions. For example, be32toh() is identical to ntohl().

The advantage of the byteorder(3) functions is that they are standard functions available on all UNIX systems. On the other hand, the fact that they were designed for use in the context of TCP/IP means that they lack the 64-bit and little-endian variants described in this page.

EXAMPLES#

The program below display the results of converting an integer from host byte order to both little-endian and big-endian byte order. Since host byte order is either little-endian or big-endian, only one of these conversions will have an effect. When we run this program on a little-endian system such as x86-32, we see the following:

$ \n./a.out\n
x.u32 = 0x44332211
htole32(x.u32) = 0x44332211
htobe32(x.u32) = 0x11223344

Program source#

#include <endian.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
int
main(void)
{
\n
    union {
\n
        uint32_t u32;
\n
        uint8_t arr[4];
\n
    } x;
\n
    x.arr[0] = 0x11;	/* Lowest-address byte */
\n
    x.arr[1] = 0x22;
\n
    x.arr[2] = 0x33;
\n
    x.arr[3] = 0x44;	/* Highest-address byte */
\n
    printf("x.u32 = %#x\n", x.u32);
\n
    printf("htole32(x.u32) = %#x\n", htole32(x.u32));
\n
    printf("htobe32(x.u32) = %#x\n", htobe32(x.u32));
\n
    exit(EXIT_SUCCESS);
}

SEE ALSO#

bswap(3), byteorder(3)