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UTF-32 (32-bit Unicode Transformation Format), sometimes called UCS-4, is a fixed-length encoding used to encode Unicode code points that uses exactly 32 bits (four bytes) per code point (but a number of leading bits must be zero as there are far fewer than 2 32 Unicode code points, needing actually only 21 bits). [1]
UTF-8, UTF-16, UTF-32 and UTF-EBCDIC have these important properties but UTF-7 and GB 18030 do not. Fixed-size characters can be helpful, but even if there is a fixed byte count per code point (as in UTF-32), there is not a fixed byte count per displayed character due to combining characters. Considering these incompatibilities and other quirks ...
encoding of non-ASCII characters in one of the Unicode transforms; negotiating the use of UTF-8 encoding in email addresses and reply codes ; sending the information about the content-transfer encoding and the Unicode transform used so that the message can be correctly displayed by the recipient (see Mojibake).
UCS-2 is an obsolete subset of UTF-16; UCS-4 and UTF-32 are functionally equivalent. UTF encodings include: UTF-8, which uses one to four 8-bit units per code point, [note 3] and has maximal compatibility with ASCII; UTF-16, which uses one 16-bit unit per code point below U+010000, and a surrogate pair of two 16-bit units per code point in the ...
The BOM for little-endian UTF-32 is the same pattern as a little-endian UTF-16 BOM followed by a UTF-16 NUL character, an unusual example of the BOM being the same pattern in two different encodings. Programmers using the BOM to identify the encoding will have to decide whether UTF-32 or UTF-16 with a NUL first character is more likely.
For UTF-8, the BOM is optional, while it is a must for the UTF-16 and the UTF-32 encodings. (Note: UTF-16 and UTF-32 without the BOM are formally known under different names, they are different encodings, and thus needs some form of encoding declaration – see UTF-16BE, UTF-16LE, UTF-32LE and UTF-32BE.) The use of the BOM character (U+FEFF ...
A code point is represented by a sequence of code units. The mapping is defined by the encoding. Thus, the number of code units required to represent a code point depends on the encoding: UTF-8: code points map to a sequence of one, two, three or four code units. UTF-16: code units are twice as long as 8-bit code units.
Unicode also adopted UTF-16, but in Unicode terminology, the high-half zone elements become "high surrogates" and the low-half zone elements become "low surrogates". [clarification needed] Another encoding, UTF-32 (previously named UCS-4), uses four bytes (total 32 bits) to encode a single character of the codespace. UTF-32 thereby permits a ...