4102 utf 16be unicode iso iec 10646

A: UTF-8 is most common on the web. UTF is used by Java and Windows. The conversions between all of them are algorithmically based, fast and lossless. This makes it easy to support data input or output in multiple formats, while using a particular UTF for internal storage or processing. The BE form uses big-endian byte serialization most significant byte first , the LE form uses little-endian byte serialization least significant byte first and the unmarked form uses big-endian byte serialization by default, but may include a byte order mark at the beginning to indicate the actual byte serialization used.

Therefore, it works well in any environment where ASCII characters have a significance as syntax characters, e. This format is not standard for text files, but well defined in the framework of the languages in question, primarily for source files.

Again, these are not standard for plain text files, but well defined within the framework of these markup languages. This format compresses Unicode into 8-bit format, preserving most of ASCII, but using some of the control codes as commands for the decoder. A: That depends on the circumstances: Of these four approaches, d uses the least space, but cannot be used transparently in most 8-bit environments.

A: All four require that the receiver can understand that format, but a is considered one of the three equivalent Unicode Encoding Forms and therefore standard. The use of b , or c out of their given context would definitely be considered non-standard, but could be a good solution for internal data transmission.

The use of SCSU is itself a standard for compressed data streams but few general purpose receivers support SCSU, so it is again most useful in internal data transmission. A: UTF-8 is the byte-oriented encoding form of Unicode. For details of its definition, see Section 2. Make sure you refer to the latest version of the Unicode Standard, as the Unicode Technical Committee has tightened the definition of UTF-8 over time to more strictly enforce unique sequences and to prohibit encoding of certain invalid characters.

Q: Is the UTF-8 encoding scheme the same irrespective of whether the underlying processor is little endian or big endian? A: Yes. Since UTF-8 is interpreted as a sequence of bytes, there is no endian problem as there is for encoding forms that use bit or bit code units. A: There is only one definition of UTF As one 4-byte sequence or as two separate 3-byte sequences? A: The definition of UTF-8 requires that supplementary characters those using surrogate pairs in UTF be encoded with a single 4-byte sequence.

However, there is a widespread practice of generating pairs of 3-byte sequences in older software, especially software which pre-dates the introduction of UTF or that is interoperating with UTF environments under particular constraints. Such an encoding is not conformant to UTF-8 as defined. When using CESU-8, great care must be taken that data is not accidentally treated as if it was UTF-8, due to the similarity of the formats.

A different issue arises if an unpaired surrogate is encountered when converting ill-formed UTF data. By representing such an unpaired surrogate on its own as a 3-byte sequence, the resulting UTF-8 data stream would become ill-formed. While it faithfully reflects the nature of the input, Unicode conformance requires that encoding form conversion always results in a valid data stream.

Therefore a converter must treat this as an error. A: UTF uses a single bit code unit to encode the most common 63K characters, and a pair of bit code units, called surrogates, to encode the 1M less commonly used characters in Unicode.

Originally, Unicode was designed as a pure bit encoding, aimed at representing all modern scripts. Ancient scripts were to be represented with private-use characters. Over time, and especially after the addition of over 14, composite characters for compatibility with legacy sets, it became clear that bits were not sufficient for the user community. Out of this arose UTF A: Surrogates are code points from two special ranges of Unicode values, reserved for use as the leading, and trailing values of paired code units in UTF They are called surrogates, since they do not represent characters directly, but only as a pair.

A: The Unicode Standard used to contain a short algorithm, now there is just a bit distribution table. Here are three short code snippets that translate the information from the bit distribution table into C code that will convert to and from UTF The next snippet does the same for the low surrogate.

Finally, the reverse, where hi and lo are the high and low surrogate, and C the resulting character. A caller would need to ensure that C, hi, and lo are in the appropriate ranges. A: There is a much simpler computation that does not try to follow the bit distribution table. They are well acquainted with the problems that variable-width codes have caused. In SJIS, there is overlap between the leading and trailing code unit values, and between the trailing and single code unit values.

This causes a number of problems: It causes false matches. It prevents efficient random access. To know whether you are on a character boundary, you have to search backwards to find a known boundary. It makes the text extremely fragile. If a unit is dropped from a leading-trailing code unit pair, many following characters can be corrupted. In UTF, the code point ranges for high and low surrogates, as well as for single units are all completely disjoint.

None of these problems occur: There are no false matches. The location of the character boundary can be directly determined from each code unit value. The vast majority of SJIS characters require 2 units, but characters using single units occur commonly and often have special importance, for example in file names.

With UTF, relatively few characters require 2 units. The vast majority of characters in common use are single code units. Certain documents, of course, may have a higher incidence of surrogate pairs, just as phthisique is an fairly infrequent word in English, but may occur quite often in a particular scholarly text. Both Unicode and ISO have policies in place that formally limit future code assignment to the integer range that can be expressed with current UTF 0 to 1,, Even if other encoding forms i.

Over a million possible codes is far more than enough for the goal of Unicode of encoding characters, not glyphs. Unicode is not designed to encode arbitrary data. A: Unpaired surrogates are invalid in UTFs. A: Not at all. Noncharacters are valid in UTFs and must be properly converted.

For more details on the definition and use of noncharacters, as well as their correct representation in each UTF, see the Noncharacters FAQ. Q: Because most supplementary characters are uncommon, does that mean I can ignore them? A: Most supplementary characters expressed with surrogate pairs in UTF are not too common.

However, that does not mean that supplementary characters should be neglected. Among them are a number of individual characters that are very popular, as well as many sets important to East Asian procurement specifications. Among the notable supplementary characters are:. A: Compared with BMP characters as a whole, the supplementary characters occur less commonly in text. This remains true now, even though many thousands of supplementary characters have been added to the standard, and a few individual characters, such as popular emoji, have become quite common.

The relative frequency of BMP characters, and of the ASCII subset within the BMP, can be taken into account when optimizing implementations for best performance: execution speed, memory usage, and data storage. Such strategies are particularly useful for UTF implementations, where BMP characters require one bit code unit to process or store, whereas supplementary characters require two.

Strategies that optimize for the BMP are less useful for UTF-8 implementations, but if the distribution of data warrants it, an optimization for the ASCII subset may make sense, as that subset only requires a single byte for processing and storage in UTF This term should now be avoided. UCS-2 does not describe a data format distinct from UTF, because both use exactly the same bit code unit representations.

However, UCS-2 does not interpret surrogate code points, and thus cannot be used to conformantly represent supplementary characters. Sometimes in the past an implementation has been labeled "UCS-2" to indicate that it does not support supplementary characters and doesn't interpret pairs of surrogate code points as characters. Such an implementation would not handle processing of character properties, code point boundaries, collation, etc.

This single 4 code unit corresponds to the Unicode scalar value, which is the abstract number associated with a Unicode character. For more information, see Section 3. A: This depends. However, the downside of UTF is that it forces you to use bits for each character, when only 21 bits are ever needed.

The number of significant bits needed for the average character in common texts is much lower, making the ratio effectively that much worse. In many situations that does not matter, and the convenience of having a fixed number of code units per character can be the deciding factor. These features were enough to swing industry to the side of using Unicode UTF While a UTF representation does make the programming model somewhat simpler, the increased average storage size has real drawbacks, making a complete transition to UTF less compelling.

With UTF APIs the low level indexing is at the storage or code unit level, with higher-level mechanisms for graphemes or words specifying their boundaries in terms of the code units.

This provides efficiency at the low levels, and the required functionality at the high levels. Hope this help to answer your questions. Alert Moderator. Alerting is not available for unauthorized users. Assigned Tags. Similar Blog Posts. Related Questions. Be the first to leave a comment. You must be Logged on to comment or reply to a post. Link Text. Open link in a new tab.

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