1 .\" Copyright (C) 2009, Linux Foundation, written by Michael Kerrisk
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4 .\" Copyright (C) 2008, Nanno Langstraat <nal@ii.nl>
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26 .TH ENDIAN 3 2009-01-19 "GNU" "Linux Programmer's Manual"
28 htobe16, htole16, be16toh, le16toh, htobe32, htole32, be32toh, le32toh,
29 htobe64, htole64, be64toh, le64toh \-
30 convert values between host and big-/little-endian byte order
33 .B #define _BSD_SOURCE
34 .B #include <endian.h>
36 .BI "uint16_t htobe16(uint16_t " host_16bits );
37 .BI "uint16_t htole16(uint16_t " host_16bits );
38 .BI "uint16_t be16toh(uint16_t " big_endian_16bits );
39 .BI "uint16_t le16toh(uint16_t " little_endian_16bits );
41 .BI "uint32_t htobe32(uint32_t " host_32bits );
42 .BI "uint32_t htole32(uint32_t " host_32bits );
43 .BI "uint32_t be32toh(uint32_t " big_endian_32bits );
44 .BI "uint32_t le32toh(uint32_t " little_endian_32bits );
46 .BI "uint64_t htobe64(uint64_t " host_64bits );
47 .BI "uint64_t htole64(uint64_t " host_64bits );
48 .BI "uint64_t be64toh(uint64_t " big_endian_64bits );
49 .BI "uint64_t le64toh(uint64_t " little_endian_64bits );
52 These functions convert the byte encoding of integer values from
53 the byte order that the current CPU (the "host") uses,
54 to and from little-endian and big-endian byte order.
58 in the name of each function indicates the size of
59 integer handled by the function, either 16, 32, or 64 bits.
61 The functions with names of the form "htobe\fInn\fP" convert
62 from host byte order to big-endian order.
64 The functions with names of the form "htole\fInn\fP" convert
65 from host byte order to little-endian order.
67 The functions with names of the form "be\fInn\fPtoh" convert
68 from big-endian order to host byte order.
70 The functions with names of the form "le\fInn\fPtoh" convert
71 from little-endian order to host byte order.
73 These function were added to glibc in version 2.9.
75 These functions are nonstandard.
76 Similar functions are present on the BSDs,
77 where the required header file is
82 NetBSD, FreeBSD, and glibc haven't followed the original
83 OpenBSD naming convention for these functions,
86 component always appears at the end of the function name
87 (thus, for example, in NetBSD, FreeBSD, and glibc,
88 the equivalent of OpenBSDs "betoh32" is "be32toh").
90 These functions are similar to the older
100 functions is that they are standard functions available
102 On the other hand, the fact that they were designed
103 for use in the context of TCP/IP means that
104 they lack the 64-bit and little-endian variants described in this page.
106 The program below display the results of converting an integer
107 from host byte order to both little-endian and big-endian byte order.
108 Since host byte order is either little-endian or big-endian,
109 only one of these conversions will have an effect.
110 When we run this program on a little-endian system such as x86-32,
111 we see the following:
117 htole32(x.u32) = 0x44332211
118 htobe32(x.u32) = 0x11223344
130 main(int argc, char *argv[])
137 x.arr[0] = 0x11; /* Lowest-address byte */
140 x.arr[3] = 0x44; /* Highest-address byte */
142 printf("x.u32 = 0x%x\\n", x.u32);
143 printf("htole32(x.u32) = 0x%x\\n", htole32(x.u32));
144 printf("htobe32(x.u32) = 0x%x\\n", htobe32(x.u32));