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@(#)utf2.4 8.1 (Berkeley) 6/4/93
$FreeBSD: head/lib/libc/locale/utf8.5 104828 2002-10-10 22:56:18Z tjr $
.Dd October 10, 2002 .Dt UTF8 5 .Os .Sh NAME .Nm utf8 .Nd "UTF-8, a transformation format of ISO 10646" .Sh SYNOPSIS .Nm ENCODING .Qq UTF-8 .Sh DESCRIPTION The .Nm UTF-8 encoding represents UCS-4 characters as a sequence of octets, using between 1 and 6 for each character. It is backwards compatible with .Tn ASCII , so 0x00-0x7f refer to the .Tn ASCII character set. The multibyte encoding of non- .Tn ASCII characters consist entirely of bytes whose high order bit is set. The actual encoding is represented by the following table: d -literal [0x00000000 - 0x0000007f] [00000000.0bbbbbbb] -> 0bbbbbbb [0x00000080 - 0x000007ff] [00000bbb.bbbbbbbb] -> 110bbbbb, 10bbbbbb [0x00000800 - 0x0000ffff] [bbbbbbbb.bbbbbbbb] -> 1110bbbb, 10bbbbbb, 10bbbbbb [0x00010000 - 0x001fffff] [00000000.000bbbbb.bbbbbbbb.bbbbbbbb] -> 11110bbb, 10bbbbbb, 10bbbbbb, 10bbbbbb [0x00200000 - 0x03ffffff] [000000bb.bbbbbbbb.bbbbbbbb.bbbbbbbb] -> 111110bb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb [0x04000000 - 0x7fffffff] [0bbbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb] -> 1111110b, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb .Ed
p If more than a single representation of a value exists (for example, 0x00; 0xC0 0x80; 0xE0 0x80 0x80) the shortest representation is always used. Longer ones are detected as an error as they pose a potential security risk, and destroy the 1:1 character:octet sequence mapping. .Sh COMPATIBILITY The .Nm encoding supersedes the .Xr utf2 4 encoding. The only differences between the two are that .Nm handles the full 31-bit character set of .Tn ISO 10646 whereas .Xr utf2 4 is limited to a 16-bit character set, and that .Xr utf2 4 accepts redundant, non-"shortest form" representations of characters. .Sh SEE ALSO .Xr euc 4 , .Xr utf2 4 .Rs .%A "F. Yergeau" .%T "UTF-8, a transformation format of ISO 10646" .%O "RFC 2279" .%D "January 1998" .Re .Sh STANDARDS The .Nm encoding is compatible with RFC 2279. .Sh BUGS Byte order marker (BOM) characters are neither added nor removed from UTF-8-encoded wide character .Xr stdio 3 streams.