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utf8 (5) Table of Contents
Nameutf8 - UTF-8, a transformation format of ISO 10646
SynopsisENCODING UTF-8"
DescriptionThe 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 ASCII, so 0x00-0x7f refer to the ASCII character set. The multibyte encoding of non-ASCII characters consist entirely of bytes whose high order bit is set. The actual encoding is represented by the following table:
[0x00000000 - 0x0000007f] [00000000.0bbbbbbb] -> 0bbbbbbb
[0x00000080 - 0x000007ff] [00000bbb.bbbbbbbb] -> 110bbbbb, 10bbbbbb
[0x00000800 - 0x0000ffff] [bbbbbbbb.bbbbbbbb] ->
1110bbbb, 10bbbbbb, 10bbbbbb
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.
CompatibilityThe utf8 encoding supersedes the utf2(4) encoding. The only differences between the two are that utf8 handles the full 31-bit character set of ISO 10646 whereas utf2(4) is limited to a 16-bit character set, and that utf2(4) accepts redundant, non-``shortest form'' representations of characters.
See Also
Rob Pike and Ken Thompson, Hello World", Proceedings of the Winter 1993 USENIX Technical Conference, USENIX Association, January 1993.
F. Yergeau, UTF-8, a transformation format of ISO 10646, January 1998, RFC 2279.
The Unicode Standard, Version 3.0, The Unicode Consortium, 2000, as amended by the Unicode Standard Annex #27: Unicode 3.1 and by the Unicode Standard Annex #28: Unicode 3.2.
StandardsThe utf8 encoding is compatible with RFC 2279 and Unicode 3.2.
BugsByte order marker (BOM) characters are neither added nor removed from UTF-8-encoded wide character stdio(3) streams.
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