1ENDIAN(3) Linux Programmer's Manual ENDIAN(3)
2
6 htobe16, htole16, be16toh, le16toh, htobe32, htole32, be32toh, le32toh,
7 htobe64, htole64, be64toh, le64toh - convert values between host and
8 big-/little-endian byte order
9
11 #define _BSD_SOURCE
12 #include <endian.h>
13 uint16_t htobe16(uint16_t host_16bits);
15 uint16_t htole16(uint16_t host_16bits);
16 uint16_t be16toh(uint16_t big_endian_16bits);
17 uint16_t le16toh(uint16_t little_endian_16bits);
18 uint32_t htobe32(uint32_t host_32bits);
20 uint32_t htole32(uint32_t host_32bits);
21 uint32_t be32toh(uint32_t big_endian_32bits);
22 uint32_t le32toh(uint32_t little_endian_32bits);
23 uint64_t htobe64(uint64_t host_64bits);
25 uint64_t htole64(uint64_t host_64bits);
26 uint64_t be64toh(uint64_t big_endian_64bits);
27 uint64_t le64toh(uint64_t little_endian_64bits);
28
30 These functions convert the byte encoding of integer values from the
31 byte order that the current CPU (the "host") uses, to and from little-
32 endian and big-endian byte order.
33 The number, nn, in the name of each function indicates the size of
35 integer handled by the function, either 16, 32, or 64 bits.
36 The functions with names of the form "htobenn" convert from host byte
38 order to big-endian order.
39 The functions with names of the form "htolenn" convert from host byte
41 order to little-endian order.
42 The functions with names of the form "benntoh" convert from big-endian
44 order to host byte order.
45 The functions with names of the form "lenntoh" convert from little-
47 endian order to host byte order.
48
50 These function were added to glibc in version 2.9.
51
53 These functions are non-standard. Similar functions are present on the
54 BSDs, where the required header file is <sys/endian.h> instead of
55 <endian.h>. Unfortunately, NetBSD, FreeBSD, and glibc haven't followed
56 the original OpenBSD naming convention for these functions, whereby the
57 nn component always appears at the end of the function name (thus, for
58 example, in NetBSD, FreeBSD, and glibc, the equivalent of OpenBSDs
59 "betoh32" is "be32toh").
60
62 These functions are similar to the older byteorder(3) family of func‐
63 tions. For example, be32toh() is identical to ntohl().
64 The advantage of the byteorder(3) functions is that they are standard
66 functions available on all Unix systems. On the other hand, the fact
67 that they were designed for use in the context of TCP/IP means that
68 they lack the 64-bit and little-endian variants described in this page.
69
71 The program below display the results of converting an integer from
72 host byte order to both little-endian and big-endian byte order. Since
73 host byte order is either little-endian or big-endian, only one of
74 these conversions will have an effect. When we run this program on a
75 little-endian system such as x86-32, we see the following:
76 $ ./a.out
78 x.u32 = 0x44332211
79 htole32(x.u32) = 0x44332211
80 htobe32(x.u32) = 0x11223344
81 Program source
83 #include <endian.h>
85 #include <stdint.h>
86 #include <stdio.h>
87 #include <stdlib.h>
88 int
90 main(int argc, char *argv[])
91 {
92 union {
93 uint32_t u32;
94 uint8_t arr[4];
95 } x;
96 x.arr[0] = 0x11; /* Lowest-address byte */
98 x.arr[1] = 0x22;
99 x.arr[2] = 0x33;
100 x.arr[3] = 0x44; /* Highest-address byte */
101 printf("x.u32 = 0x%x\n", x.u32);
103 printf("htole32(x.u32) = 0x%x\n", htole32(x.u32));
104 printf("htobe32(x.u32) = 0x%x\n", htobe32(x.u32));
105 exit(EXIT_SUCCESS);
107 }
108
110 byteorder(3)
111
113 This page is part of release 3.22 of the Linux man-pages project. A
114 description of the project, and information about reporting bugs, can
115 be found at http://www.kernel.org/doc/man-pages/.
116GNU 2009-01-19 ENDIAN(3)