htobe16, htole16, be16toh, le16toh, htobe32, htole32, be32toh, le32toh, htobe64, htole64, be64toh,

       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.

       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

   Programsource

       #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);
       }

       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.

       Standard C library (libc, -lc)

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

bswap(3), byteorder(3)

Linux man-pages 6.9.1                              2024-06-15                                          endian(3)

       None.

#include<endian.h>uint16_thtobe16(uint16_thost_16bits);uint16_thtole16(uint16_thost_16bits);uint16_tbe16toh(uint16_tbig_endian_16bits);uint16_tle16toh(uint16_tlittle_endian_16bits);uint32_thtobe32(uint32_thost_32bits);uint32_thtole32(uint32_thost_32bits);uint32_tbe32toh(uint32_tbig_endian_32bits);uint32_tle32toh(uint32_tlittle_endian_32bits);uint64_thtobe64(uint64_thost_64bits);uint64_thtole64(uint64_thost_64bits);uint64_tbe64toh(uint64_tbig_endian_64bits);uint64_tle64toh(uint64_tlittle_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

       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").