ENDIAN(3)                                           Linux Programmer's Manual                                          ENDIAN(3)



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

SYNOPSIS
       #define _BSD_SOURCE
       #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 function 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 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").

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 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



GNU                                                        2009-01-19                                                  ENDIAN(3)