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

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

       #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);

       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.

       These function were added to glibc in version 2.9.

       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  func-
       tion  name  (thus,  for  example,  in  NetBSD,  FreeBSD,  and  glibc,  the  equivalent of OpenBSDs "betoh32" is

       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.

       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  conver-
       sions  will have an effect.  When we run this program on a little-endian system such as x86-32, we see the fol-

           $ ./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>

       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));



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GNU                               2009-01-19                         ENDIAN(3)