man3/endian.3

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  28 .TH ENDIAN 3  2016-10-08 "GNU" "Linux Programmer's Manual"
  29 .SH NAME
  30 htobe16, htole16, be16toh, le16toh, htobe32, htole32, be32toh, le32toh,
  31 htobe64, htole64, be64toh, le64toh \-
  32 convert values between host and big-/little-endian byte order
  33 .SH SYNOPSIS
  34 .nf
  35 .B #include <endian.h>
  36
  37 .BI "uint16_t htobe16(uint16_t " host_16bits );
  38 .BI "uint16_t htole16(uint16_t " host_16bits );
  39 .BI "uint16_t be16toh(uint16_t " big_endian_16bits );
  40 .BI "uint16_t le16toh(uint16_t " little_endian_16bits );
  41
  42 .BI "uint32_t htobe32(uint32_t " host_32bits );
  43 .BI "uint32_t htole32(uint32_t " host_32bits );
  44 .BI "uint32_t be32toh(uint32_t " big_endian_32bits );
  45 .BI "uint32_t le32toh(uint32_t " little_endian_32bits );
  46
  47 .BI "uint64_t htobe64(uint64_t " host_64bits );
  48 .BI "uint64_t htole64(uint64_t " host_64bits );
  49 .BI "uint64_t be64toh(uint64_t " big_endian_64bits );
  50 .BI "uint64_t le64toh(uint64_t " little_endian_64bits );
  51 .fi
  52 .sp
  53 .in -4n
  54 Feature Test Macro Requirements for glibc (see
  55 .BR feature_test_macros (7)):
  56 .in
  57 .sp
  58 .BR htobe16 (),
  59 .BR htole16 (),
  60 .BR be16toh (),
  61 .BR le16toh (),
  62 .BR htobe32 (),
  63 .BR htole32 (),
  64 .BR be32toh (),
  65 .BR le32toh (),
  66 .BR htobe64 (),
  67 .BR htole64 (),
  68 .BR be64toh (),
  69 .BR le64toh ():
  70 .nf
  71     Since glibc 2.19:
  72         _DEFAULT_SOURCE
  73     In glibc up to and including 2.19:
  74         _BSD_SOURCE
  75 .fi
  76 .SH DESCRIPTION
  77 These functions convert the byte encoding of integer values from
  78 the byte order that the current CPU (the "host") uses,
  79 to and from little-endian and big-endian byte order.
  80
  81 The number,
  82 .IR nn ,
  83 in the name of each function indicates the size of
  84 integer handled by the function, either 16, 32, or 64 bits.
  85
  86 The functions with names of the form "htobe\fInn\fP" convert
  87 from host byte order to big-endian order.
  88
  89 The functions with names of the form "htole\fInn\fP" convert
  90 from host byte order to little-endian order.
  91
  92 The functions with names of the form "be\fInn\fPtoh" convert
  93 from big-endian order to host byte order.
  94
  95 The functions with names of the form "le\fInn\fPtoh" convert
  96 from little-endian order to host byte order.
  97 .SH VERSIONS
  98 These functions were added to glibc in version 2.9.
  99 .SH CONFORMING TO
 100 These functions are nonstandard.
 101 Similar functions are present on the BSDs,
 102 where the required header file is
 103 .I <sys/endian.h>
 104 instead of
 105 .IR <endian.h> .
 106 Unfortunately,
 107 NetBSD, FreeBSD, and glibc haven't followed the original
 108 OpenBSD naming convention for these functions,
 109 whereby the
 110 .I nn
 111 component always appears at the end of the function name
 112 (thus, for example, in NetBSD, FreeBSD, and glibc,
 113 the equivalent of OpenBSDs "betoh32" is "be32toh").
 114 .SH NOTES
 115 These functions are similar to the older
 116 .BR byteorder (3)
 117 family of functions.
 118 For example,
 119 .BR be32toh ()
 120 is identical to
 121 .BR ntohl ().
 122
 123 The advantage of the
 124 .BR byteorder (3)
 125 functions is that they are standard functions available
 126 on all UNIX systems.
 127 On the other hand, the fact that they were designed
 128 for use in the context of TCP/IP means that
 129 they lack the 64-bit and little-endian variants described in this page.
 130 .SH EXAMPLE
 131 The program below display the results of converting an integer
 132 from host byte order to both little-endian and big-endian byte order.
 133 Since host byte order is either little-endian or big-endian,
 134 only one of these conversions will have an effect.
 135 When we run this program on a little-endian system such as x86-32,
 136 we see the following:
 137 .in +4n
 138 .nf
 139
 140 $ \fB./a.out\fP
 141 x.u32 = 0x44332211
 142 htole32(x.u32) = 0x44332211
 143 htobe32(x.u32) = 0x11223344
 144 .fi
 145 .in
 146 .SS Program source
 147 \&
 148 .nf
 149 #include <endian.h>
 150 #include <stdint.h>
 151 #include <stdio.h>
 152 #include <stdlib.h>
 153
 154 int
 155 main(int argc, char *argv[])
 156 {
 157     union {
 158         uint32_t u32;
 159         uint8_t arr[4];
 160     } x;
 161
 162     x.arr[0] = 0x11;    /* Lowest-address byte */
 163     x.arr[1] = 0x22;
 164     x.arr[2] = 0x33;
 165     x.arr[3] = 0x44;    /* Highest-address byte */
 166
 167     printf("x.u32 = 0x%x\\n", x.u32);
 168     printf("htole32(x.u32) = 0x%x\\n", htole32(x.u32));
 169     printf("htobe32(x.u32) = 0x%x\\n", htobe32(x.u32));
 170
 171     exit(EXIT_SUCCESS);
 172 }
 173 .fi
 174 .SH SEE ALSO
 175 .BR bswap (3),
 176 .BR byteorder (3)