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UTF-8 is a variable width character encoding capable of encoding all 1,  valid code points in Unicode using one to four 8-bit bytes. Code points with lower numerical values, which tend to occur more frequently, are encoded using fewer bytes.
UTF-8 has been the dominant character encoding for the World Wide Web sinceas it's most popular in every country,  and as of April accounts for Since the restriction of the Unicode code-space to bit values inUTF-8 is defined to encode code points in one to four bytes, depending on the number of significant bits in the numerical value of the code point.
The following table shows the structure of the encoding. The x characters are replaced by the bits of the code point. The next 1, characters need two bytes to encode, which covers the remainder of almost all Latin-script alphabetsand also GreekCyrillicCopticArmenianHebrewArabicSyriacThaana and N'Ko alphabets, as well as Combining Diacritical Marks. Three bytes are needed for characters in the rest of the Basic Multilingual Planeh using convert with binary and character database contains virtually all characters in common use  including most Chinese, Japanese and Korean characters.
Four bytes are needed for characters in the other planes of Unicodewhich include less common CJK charactersvarious historic scripts, mathematical symbols, and emoji pictographic symbols.
The three bytes 10 00 10 10 can be more concisely written in hexadecimal, as E2 82 AC. Since UTF-8 uses groups of six bits, it is sometimes useful to use octal notation which uses 3-bit groups.
With a calculator which can convert between hexadecimal and octal it can be easier to manually create or interpret UTF-8 compared with using binary. The following table summarises this conversion, as well as others with different lengths in UTF The colors indicate how bits from the code point are distributed among the UTF-8 bytes. Additional bits added by the UTF-8 encoding process are shown in black. The following table summarizes usage of UTF-8 code units individual bytes or octets in a code page format.
Orange cells with a large dot are continuation bytes. White cells are the leading bytes for a sequence of multiple bytes, the length shown at the left edge of the row. The text shows the Unicode blocks encoded by sequences starting with this byte, and the hexadecimal code point shown in the cell is the lowest character value encoded using that leading byte. Red cells must never appear in a valid UTF-8 sequence. The first two red cells C0 and C1 could be used only for a two-byte encoding of a 7-bit ASCII character which should be encoded in one byte; as described below such "overlong" sequences are disallowed.
Pink cells are the leading bytes for a sequence of multiple bytes, h using convert with binary and character database which some, but not all, possible continuation sequences are valid.
E0 and F0 could start overlong encodings, in this case the lowest non-overlong-encoded code point is shown. In principle, it would be possible to h using convert with binary and character database the number of bytes in an encoding by padding the code point with leading 0s. This is called an overlong encoding.
The standard specifies that the correct encoding of a code point use only the minimum number of bytes required to hold the significant bits of the h using convert with binary and character database point. Longer encodings are called overlong and are not valid UTF-8 representations of the code point. This rule maintains a one-to-one correspondence between code points and their valid encodings, so that there is h using convert with binary and character database unique valid encoding for each code point.
This ensures that string comparisons and searches are well-defined. This allows the byte 00 to be used as a string terminator. Many earlier decoders would happily try to decode these. This guarantees that it will neither interpret nor emit an ill-formed code unit sequence.
Many UTF-8 decoders throw exceptions on encountering errors. Early versions of Python 3. More recent converters translate the first byte of an invalid sequence to a replacement character and continue parsing with the next byte. These error bytes will always have the high bit set. This avoids denial-of-service bugs, and it is very common in text rendering such as browser display, since mangled text is probably more useful than nothing for helping the user figure out what the string was supposed to contain.
These replacement algorithms are " lossy ", as more than one sequence is translated to the same code point. This means that it would not be possible to reliably convert back to the original encoding, therefore losing information. But this runs into practical difficulties: The large number of invalid byte sequences provides the advantage of making it easy to have a program accept both UTF-8 and legacy encodings such as ISO Software can check for UTF-8 correctness, and if that fails assume the input to be in the legacy encoding.
To preserve these invalid UTF sequences, their corresponding UTF-8 encodings are sometimes allowed by implementations despite the above rule. This spelling is used in all the Unicode Consortium documents relating to the encoding.
Other descriptions that omit the hyphen or replace it with a space, such as "utf8" or "UTF 8", are not accepted as correct by the governing standards. Supported Windows versions, i. Windows 7 and later, have codepageas a synonym for UTF-8 with better support than in older Windows and Microsoft has a script for Windows 10, to enable it by default for its notepad program.
The following implementations show slight differences from the UTF-8 specification. In such programs each half of a UTF surrogate pair is encoded as its own three-byte UTF-8 encoding, resulting in six-byte sequences rather than four bytes for characters outside the Basic Multilingual Plane. Although this non-optimal encoding is generally not deliberate, a supposed benefit is that it preserves UTF binary sorting order when CESU-8 is binary sorted.
In normal usage, the Java programming language supports standard UTF-8 when reading and writing strings through InputStreamReader and OutputStreamWriter if it is the platform's default character set or as requested by the program.
However it uses Modified UTF-8 for object serialization  among other applications of DataInput and DataOutputfor the Java Native Interface and for embedding constant strings in class files.
Many systems that deal with UTF-8 work this way without considering it a different encoding, as it is simpler. Software that is not aware of multibyte encodings will display the BOM as three garbage characters at the start of the document, e. The Unicode Standard neither requires nor recommends the use of the BOM for UTF-8, but warns that it may be encountered at the start of a file as a transcoding artifact. H using convert with binary and character database earlythe search was on for a good byte stream encoding of multi-byte character sets.
The draft ISO standard contained a non-required annex called UTF-1 that provided a byte stream encoding of its bit code points. This encoding was not satisfactory on performance grounds, among other problems, and the biggest problem was probably that it did h using convert with binary and character database have a clear separation between ASCII and non-ASCII: The table below was derived from a textual description in the annex.
Dave Prosser of H using convert with binary and character database System Laboratories submitted a proposal for one that had faster implementation characteristics and introduced the improvement that 7-bit ASCII characters would only represent themselves; all multibyte sequences would include only bytes where the high bit was set. A modification by Ken Thompson of the Plan 9 operating system group at Bell Labs made it somewhat less bit-efficient than the previous proposal but crucially allowed it to be self-synchronizingletting a reader start anywhere and immediately detect byte sequence boundaries.
It also abandoned the use of biases and instead added the rule that only the shortest possible encoding is allowed; the additional loss in compactness is relatively insignificant, but readers now have to look out for invalid encodings to avoid reliability and especially security issues. Thompson's design was outlined on September 2,on a placemat in a New Jersey diner with Rob Pike. They are all the same in their general mechanics, with the main differences being on issues such as allowed range of code point values and safe handling of invalid input.
From Wikipedia, the free encyclopedia. UTF-8 historyFrom: Wed, 30 Apr UTF-8 was designed, in front of my eyes, on a placemat in a New Jersey diner one night in September or so So that night Ken wrote packing and unpacking code and I started h using convert with binary and character database into the C and graphics libraries.
The next day all the code was done The Unicode Standard 6. Mountain View, California, US: Archived from the original on The Basic Multilingual Plane BMP, or Plane 0 contains the common-use characters for all the modern scripts of the world as well as many historical and rare characters.
By far the majority of all Unicode characters for almost all textual data can be found in the BMP. Internet Engineering Task Force. UTF-8, and why it need not matter". Internet Assigned Numbers Authority. Significant limitations do remain - in particular redirection and piping still fail under codepage Nevertheless, the added support opens up some new exciting possibilities.
Java virtual machine UTF-8 strings never have embedded nulls. Object Serialization Stream Protocol, section 2: Android Open Source Project. UTF-8 bit by bit Revision 6 ". The Unicode Standard 1. Archived PDF from the original on Scripts and symbols in Unicode. Combining marks Diacritics Punctuation Space Numbers. Plan 9 from Bell Labs Inferno. Newsqueak Limbo Go Sawzall.
Unix Plan 9 from Bell Labs. Belle ed grep sam Space Travel Thompson shell. Retrieved from " https: CS1 Japanese-language sources ja All articles with unsourced statements Articles with unsourced statements from August Articles with unsourced statements from March Articles with unsourced statements h using convert with binary and character database December Pages using RFC magic links.