ENDIAN(3)                           Linux Programmer's Manual                           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

SYNOPSIS
       #define _BSD_SOURCE             /* See feature_test_macros(7) */
       #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);

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
       These functions were added to glibc in version 2.9.

CONFORMING TO
       These functions are nonstandard.  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 func‐
       tions,  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").

NOTES
       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.

EXAMPLE
       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(int argc, char *argv[])
       {
           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 = 0x%x\n", x.u32);
           printf("htole32(x.u32) = 0x%x\n", htole32(x.u32));
           printf("htobe32(x.u32) = 0x%x\n", htobe32(x.u32));

           exit(EXIT_SUCCESS);
       }

SEE ALSO
       byteorder(3)

COLOPHON
       This page is part of release 3.74 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at http://www.kernel.org/doc/man-pages/.



GNU                                         2010-09-10                                  ENDIAN(3)