endian(3) — Linux manual page

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | VERSIONS | STANDARDS | HISTORY | EXAMPLES | SEE ALSO | COLOPHON

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
   feature_test_macros(7)):

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

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

       None.

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>

       int
       main(void)
       {
           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));

           exit(EXIT_SUCCESS);
       }

SEE ALSO         top

       bswap(3), byteorder(3)

COLOPHON         top

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Linux man-pages 6.10            2024-07-23                      endian(3)

Pages that refer to this page: bswap(3)byteorder(3)