endian(3) — Linux manual page


endian(3)               Library Functions Manual               endian(3)

NAME         top

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

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <endian.h>

       uint16_t htobe16(uint16_t host_16bits);
       uint16_t htole16(uint16_t host_16bits);
       uint16_t be16toh(uint16_t big_endian_16bits);
       uint16_t le16toh(uint16_t little_endian_16bits);

       uint32_t htobe32(uint32_t host_32bits);
       uint32_t htole32(uint32_t host_32bits);
       uint32_t be32toh(uint32_t big_endian_32bits);
       uint32_t le32toh(uint32_t little_endian_32bits);

       uint64_t htobe64(uint64_t host_64bits);
       uint64_t htole64(uint64_t host_64bits);
       uint64_t be64toh(uint64_t big_endian_64bits);
       uint64_t le64toh(uint64_t little_endian_64bits);

   Feature Test Macro Requirements for glibc (see

       htobe16(), htole16(), be16toh(), le16toh(), htobe32(), htole32(),
       be32toh(), le32toh(), htobe64(), htole64(), be64toh(), le64toh():
           Since glibc 2.19:
           In glibc up to and including 2.19:

DESCRIPTION         top

       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         top

       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         top


HISTORY         top

       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         top

       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:

           $ ./a.out
           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>

           union {
               uint32_t u32;
               uint8_t arr[4];
           } x;

           x.arr[0] = 0x11;    /* Lowest-address byte */
           x.arr[1] = 0x22;
           x.arr[2] = 0x33;
           x.arr[3] = 0x44;    /* Highest-address byte */

           printf("x.u32 = %#x\n", x.u32);
           printf("htole32(x.u32) = %#x\n", htole32(x.u32));
           printf("htobe32(x.u32) = %#x\n", htobe32(x.u32));


SEE ALSO         top

       bswap(3), byteorder(3)

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