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 #include <endian.h>
12 uint16_t htobe16(uint16_t host_16bits);
14 uint16_t htole16(uint16_t host_16bits);
15 uint16_t be16toh(uint16_t big_endian_16bits);
16 uint16_t le16toh(uint16_t little_endian_16bits);
17 uint32_t htobe32(uint32_t host_32bits);
19 uint32_t htole32(uint32_t host_32bits);
20 uint32_t be32toh(uint32_t big_endian_32bits);
21 uint32_t le32toh(uint32_t little_endian_32bits);
22 uint64_t htobe64(uint64_t host_64bits);
24 uint64_t htole64(uint64_t host_64bits);
25 uint64_t be64toh(uint64_t big_endian_64bits);
26 uint64_t le64toh(uint64_t little_endian_64bits);
27 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
29 htobe16(), htole16(), be16toh(), le16toh(), htobe32(), htole32(),
31 be32toh(), le32toh(), htobe64(), htole64(), be64toh(), le64toh():
32 Since glibc 2.19:
33 _DEFAULT_SOURCE
34 In glibc up to and including 2.19:
35 _BSD_SOURCE
36
38 These functions convert the byte encoding of integer values from the
39 byte order that the current CPU (the "host") uses, to and from little-
40 endian and big-endian byte order.
41 The number, nn, in the name of each function indicates the size of in‐
43 teger handled by the function, either 16, 32, or 64 bits.
44 The functions with names of the form "htobenn" convert from host byte
46 order to big-endian order.
47 The functions with names of the form "htolenn" convert from host byte
49 order to little-endian order.
50 The functions with names of the form "benntoh" convert from big-endian
52 order to host byte order.
53 The functions with names of the form "lenntoh" convert from little-en‐
55 dian order to host byte order.
56
58 These functions were added to glibc in version 2.9.
59
61 These functions are nonstandard. Similar functions are present on the
62 BSDs, where the required header file is <sys/endian.h> instead of <en‐
63 dian.h>. Unfortunately, NetBSD, FreeBSD, and glibc haven't followed
64 the original OpenBSD naming convention for these functions, whereby the
65 nn component always appears at the end of the function name (thus, for
66 example, in NetBSD, FreeBSD, and glibc, the equivalent of OpenBSDs "be‐
67 toh32" is "be32toh").
68
70 These functions are similar to the older byteorder(3) family of func‐
71 tions. For example, be32toh() is identical to ntohl().
72 The advantage of the byteorder(3) functions is that they are standard
74 functions available on all UNIX systems. On the other hand, the fact
75 that they were designed for use in the context of TCP/IP means that
76 they lack the 64-bit and little-endian variants described in this page.
77
79 The program below display the results of converting an integer from
80 host byte order to both little-endian and big-endian byte order. Since
81 host byte order is either little-endian or big-endian, only one of
82 these conversions will have an effect. When we run this program on a
83 little-endian system such as x86-32, we see the following:
84 $ ./a.out
86 x.u32 = 0x44332211
87 htole32(x.u32) = 0x44332211
88 htobe32(x.u32) = 0x11223344
89 Program source
91 #include <endian.h>
93 #include <stdint.h>
94 #include <stdio.h>
95 #include <stdlib.h>
96 int
98 main(int argc, char *argv[])
99 {
100 union {
101 uint32_t u32;
102 uint8_t arr[4];
103 } x;
104 x.arr[0] = 0x11; /* Lowest-address byte */
106 x.arr[1] = 0x22;
107 x.arr[2] = 0x33;
108 x.arr[3] = 0x44; /* Highest-address byte */
109 printf("x.u32 = %#x\n", x.u32);
111 printf("htole32(x.u32) = %#x\n", htole32(x.u32));
112 printf("htobe32(x.u32) = %#x\n", htobe32(x.u32));
113 exit(EXIT_SUCCESS);
115 }
116
118 bswap(3), byteorder(3)
119
121 This page is part of release 5.12 of the Linux man-pages project. A
122 description of the project, information about reporting bugs, and the
123 latest version of this page, can be found at
124 https://www.kernel.org/doc/man-pages/.
125GNU 2021-03-22 ENDIAN(3)