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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
       #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 lit-
       tle-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 non-standard.  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  fol-
       lowing:

           $ ./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 3.22 of the Linux man-pages project.  A description of
       the project, and information about reporting bugs, can be found at  http://www.ker-
       nel.org/doc/man-pages/.



GNU                               2009-01-19                         ENDIAN(3)

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