1.\" Copyright (c) 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" Paul Borman at Krystal Technologies. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 4. Neither the name of the University nor the names of its contributors 16.\" may be used to endorse or promote products derived from this software 17.\" without specific prior written permission. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 23.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" @(#)utf2.4 8.1 (Berkeley) 6/4/93 32.\" $FreeBSD: head/lib/libc/locale/utf8.5 165903 2007-01-09 00:28:16Z imp $ 33.\" 34.Dd April 7, 2004 35.Dt UTF8 5 36.Os 37.Sh NAME 38.Nm utf8 39.Nd "UTF-8, a transformation format of ISO 10646" 40.Sh SYNOPSIS 41.Nm ENCODING 42.Qq UTF-8 43.Sh DESCRIPTION 44The 45.Nm UTF-8 46encoding represents UCS-4 characters as a sequence of octets, using 47between 1 and 6 for each character. 48It is backwards compatible with 49.Tn ASCII , 50so 0x00-0x7f refer to the 51.Tn ASCII 52character set. 53The multibyte encoding of 54.No non- Ns Tn ASCII 55characters 56consist entirely of bytes whose high order bit is set. 57The actual 58encoding is represented by the following table: 59.Bd -literal 60[0x00000000 - 0x0000007f] [00000000.0bbbbbbb] -> 0bbbbbbb 61[0x00000080 - 0x000007ff] [00000bbb.bbbbbbbb] -> 110bbbbb, 10bbbbbb 62[0x00000800 - 0x0000ffff] [bbbbbbbb.bbbbbbbb] -> 63 1110bbbb, 10bbbbbb, 10bbbbbb 64[0x00010000 - 0x001fffff] [00000000.000bbbbb.bbbbbbbb.bbbbbbbb] -> 65 11110bbb, 10bbbbbb, 10bbbbbb, 10bbbbbb 66[0x00200000 - 0x03ffffff] [000000bb.bbbbbbbb.bbbbbbbb.bbbbbbbb] -> 67 111110bb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb 68[0x04000000 - 0x7fffffff] [0bbbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb] -> 69 1111110b, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb 70.Ed 71.Pp 72If more than a single representation of a value exists (for example, 730x00; 0xC0 0x80; 0xE0 0x80 0x80) the shortest representation is always 74used. 75Longer ones are detected as an error as they pose a potential 76security risk, and destroy the 1:1 character:octet sequence mapping. 77.Sh SEE ALSO 78.Xr euc 5 79.Rs 80.%A "Rob Pike" 81.%A "Ken Thompson" 82.%T "Hello World" 83.%J "Proceedings of the Winter 1993 USENIX Technical Conference" 84.%Q "USENIX Association" 85.%D "January 1993" 86.Re 87.Rs 88.%A "F. Yergeau" 89.%T "UTF-8, a transformation format of ISO 10646" 90.%O "RFC 2279" 91.%D "January 1998" 92.Re 93.Rs 94.%Q "The Unicode Consortium" 95.%T "The Unicode Standard, Version 3.0" 96.%D "2000" 97.%O "as amended by the Unicode Standard Annex #27: Unicode 3.1 and by the Unicode Standard Annex #28: Unicode 3.2" 98.Re 99.Sh STANDARDS 100The 101.Nm 102encoding is compatible with RFC 2279 and Unicode 3.2. 103