UTF2(5) File Formats Manual UTF2(5)

utf2Universal character set Transformation Format encoding of runes


The UTF2 encoding has been deprecated in favour of UTF-8.

New applications should not use UTF2.

The UTF2 encoding is based on a proposed X-Open multibyte FSS-UCS-TF (File System Safe Universal Character Set Transformation Format) encoding as used in . Although it is capable of representing more than 16 bits, the current implementation is limited to 16 bits as defined by the Unicode Standard.

UTF2 representation is backwards compatible with ASCII, so 0x00-0x7f refer to the ASCII character set. The multibyte encoding of runes between 0x0080 and 0xffff consist entirely of bytes whose high order bit is set. The actual encoding is represented by the following table:

[0x0000 - 0x007f] [00000000.0bbbbbbb] -> 0bbbbbbb
[0x0080 - 0x07ff] [00000bbb.bbbbbbbb] -> 110bbbbb, 10bbbbbb
[0x0800 - 0xffff] [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 (but the longer ones will be correctly decoded).

The final three encodings provided by X-Open:

[00000000.000bbbbb.bbbbbbbb.bbbbbbbb] ->
	11110bbb, 10bbbbbb, 10bbbbbb, 10bbbbbb

[000000bb.bbbbbbbb.bbbbbbbb.bbbbbbbb] ->
	111110bb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb

[0bbbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb] ->
	1111110b, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb

which provides for the entire proposed ISO-10646 31 bit standard are currently not implemented.

mklocale(1), setlocale(3), utf8(5)

October 11, 2002 macOS 14.4