UTF-8

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UTF-8 (U from Universal Character Set + Transformation Format—8-bit[1]) is a character encoding capable of encoding all possible characters (called code points) in Unicode. The encoding is variable-length and uses 8-bit code units. It was designed for backward compatibility with ASCII and to avoid the complications of endianness and byte order marks in UTF-16 and UTF-32.

Graph indicating that UTF-8 (light blue) exceeded other main encodings of text on the Web in December 2007, and that by 2010 it was nearing 50% and up to 81% in 2014. Encodings were detected by examining the text, not from the encoding tag in the header,[2] thus does not include ASCII tagged as UTF-8. As ASCII is valid UTF-8 it could be added to the UTF-8 to get over 65% usage.

UTF-8 has become the dominant character encoding for the World Wide Web, accounting for 81.4% of all Web pages in November 2014 (with most popular East Asian encoding at 1.4% and all of them combined under 5%).[3][2][4] The Internet Mail Consortium (IMC) recommends that all e-mail programs be able to display and create mail using UTF-8.[5] The W3C recommends UTF-8 as default encoding in their main standards (XML and HTML).

UTF-8 encodes each of the 1,112,064 valid code points in the Unicode code space (1,114,112 code points minus 2,048 surrogate code points) using one to four 8-bit bytes (a group of 8 bits is known as an octet in the Unicode Standard). Code points with lower numerical values (i.e. earlier code positions in the Unicode character set, which tend to occur more frequently) are encoded using fewer bytes. The first 128 characters of Unicode, which correspond one-to-one with ASCII, are encoded using a single octet with the same binary value as ASCII, making valid ASCII text valid UTF-8-encoded Unicode as well.

The official IANA code for the UTF-8 character encoding is UTF-8.[6]

History[edit]

By early 1992, the search was on for a good byte-stream encoding of multi-byte character sets. The draft ISO 10646 standard contained a non-required annex called UTF-1 that provided a byte-stream encoding of its 32-bit code points. This encoding was not satisfactory on performance grounds, but did introduce the notion that bytes in the range of 0–127 continue representing the ASCII characters in UTF, thereby providing backward compatibility with ASCII.

In July 1992, the X/Open committee XoJIG was looking for a better encoding. Dave Prosser of Unix 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. This original proposal, the File System Safe UCS Transformation Format (FSS-UTF), was similar in concept to UTF-8, but lacked the crucial property of self-synchronization.[7][8]

In August 1992, this proposal was circulated by an IBM X/Open representative to interested parties. Ken Thompson of the Plan 9 operating system group at Bell Labs made a small but crucial modification to the encoding, making it very slightly less bit-efficient than the previous proposal but allowing it to be self-synchronizing, meaning that it was no longer necessary to read from the beginning of the string to find code point boundaries. Thompson's design was outlined on September 2, 1992, on a placemat in a New Jersey diner with Rob Pike. In the following days, Pike and Thompson implemented it and updated Plan 9 to use it throughout, and then communicated their success back to X/Open.[7]

UTF-8 was first officially presented at the USENIX conference in San Diego, from January 25 to 29, 1993.

Google reported that in 2008 UTF-8 (misleadingly labelled "Unicode") became the most common encoding for HTML files.[9][10]

Description[edit]

The design of UTF-8 can be seen in this table of the scheme as originally proposed by Dave Prosser and subsequently modified by Ken Thompson (the x characters are replaced by the bits of the code point):

Bits of
code point
First
code point
Last
code point
Bytes in
sequence
Byte 1Byte 2Byte 3Byte 4Byte 5Byte 6
  7U+0000U+007F10xxxxxxx
11U+0080U+07FF2110xxxxx10xxxxxx
16U+0800U+FFFF31110xxxx10xxxxxx10xxxxxx
21U+10000U+1FFFFF411110xxx10xxxxxx10xxxxxx10xxxxxx
The patterns below are not part of UTF-8, but were part of the first specification.
26U+200000U+3FFFFFF5111110xx10xxxxxx10xxxxxx10xxxxxx10xxxxxx
31U+4000000U+7FFFFFFF61111110x10xxxxxx10xxxxxx10xxxxxx10xxxxxx10xxxxxx

The original specification covered numbers up to 31 bits (the original limit of the Universal Character Set). In November 2003, UTF-8 was restricted by RFC 3629 to end at U+10FFFF, in order to match the constraints of the UTF-16 character encoding. This removed all 5- and 6-byte sequences, and about half of the 4-byte sequences.

The salient features of this scheme are as follows:

The first 128 characters (US-ASCII) need one byte. The next 1,920 characters need two bytes to encode. This covers the remainder of almost all Latin alphabets, and also Greek, Cyrillic, Coptic, Armenian, Hebrew, Arabic, Syriac and Tāna alphabets, as well as Combining Diacritical Marks. Three bytes are needed for characters in the rest of the Basic Multilingual Plane (which contains virtually all characters in common use[11]). Four bytes are needed for characters in the other planes of Unicode, which include less common CJK characters, various historic scripts, mathematical symbols, and emoji (pictographic symbols).

Examples[edit]

Consider the encoding of the Euro sign, €.

  1. The Unicode code point for "€" is U+20AC.
  2. According to the scheme table above, this will take three bytes to encode, since it is between U+0800 and U+FFFF.
  3. Hexadecimal 20AC is binary 0010000010101100. The two leading zeros are added because, as the scheme table shows, a three-byte encoding needs exactly sixteen bits from the code point.
  4. Because it is a three-byte encoding, the leading byte starts with three 1s, then a 0 (1110 ...)
  5. The remaining bits of this byte are taken from the code point (11100010), leaving ... 000010101100.
  6. Each of the continuation bytes starts with 10 and takes six bits of the code point (so 10000010, then 10101100).

The three bytes 11100010 10000010 10101100 can be more concisely written in hexadecimal, as E2 82 AC.

The following table summarises this conversion, as well as others with different lengths in UTF-8. 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.

CharacterBinary code pointBinary UTF-8Hexadecimal UTF-8
$U+002401001000010010024
¢U+00A2000 1010001011000010 10100010C2 A2
U+20AC00100000 1010110011100010 10000010 10101100E2 82 AC
𤭢U+24B6200010 01001011 0110001011110000 10100100 10101101 10100010F0 A4 AD A2

Codepage layout[edit]

UTF-8
_0_1_2_3_4_5_6_7_8_9_A_B_C_D_E_F
 
0_
 
NUL
0000
0
SOH
0001
1
STX
0002
2
ETX
0003
3
EOT
0004
4
ENQ
0005
5
ACK
0006
6
BEL
0007
7
BS
0008
8
HT
0009
9
LF
000A
10
VT
000B
11
FF
000C
12
CR
000D
13
SO
000E
14
SI
000F
15
 
1_
 
DLE
0010
16
DC1
0011
17
DC2
0012
18
DC3
0013
19
DC4
0014
20
NAK
0015
21
SYN
0016
22
ETB
0017
23
CAN
0018
24
EM
0019
25
SUB
001A
26
ESC
001B
27
FS
001C
28
GS
001D
29
RS
001E
30
US
001F
31
 
2_
 
SP
0020
32
!
0021
33
"
0022
34
#
0023
35
$
0024
36
%
0025
37
&
0026
38
'
0027
39
(
0028
40
)
0029
41
*
002A
42
+
002B
43
,
002C
44
-
002D
45
.
002E
46
/
002F
47
 
3_
 
0
0030
48
1
0031
49
2
0032
50
3
0033
51
4
0034
52
5
0035
53
6
0036
54
7
0037
55
8
0038
56
9
0039
57
:
003A
58
;
003B
59
<
003C
60
=
003D
61
>
003E
62
?
003F
63
 
4_
 
@
0040
64
A
0041
65
B
0042
66
C
0043
67
D
0044
68
E
0045
69
F
0046
70
G
0047
71
H
0048
72
I
0049
73
J
004A
74
K
004B
75
L
004C
76
M
004D
77
N
004E
78
O
004F
79
 
5_
 
P
0050
80
Q
0051
81
R
0052
82
S
0053
83
T
0054
84
U
0055
85
V
0056
86
W
0057
87
X
0058
88
Y
0059
89
Z
005A
90
[
005B
91
\
005C
92
]
005D
93
^
005E
94
_
005F
95
 
6_
 
`
0060
96
a
0061
97
b
0062
98
c
0063
99
d
0064
100
e
0065
101
f
0066
102
g
0067
103
h
0068
104
i
0069
105
j
006A
106
k
006B
107
l
006C
108
m
006D
109
n
006E
110
o
006F
111
 
7_
 
p
0070
112
q
0071
113
r
0072
114
s
0073
115
t
0074
116
u
0075
117
v
0076
118
w
0077
119
x
0078
120
y
0079
121
z
007A
122
{
007B
123
|
007C
124
}
007D
125
~
007E
126
DEL
007F
127
 
8_
 

+00
128

+01
129

+02
130

+03
131

+04
132

+05
133

+06
134

+07
135

+08
136

+09
137

+0A
138

+0B
139

+0C
140

+0D
141

+0E
142

+0F
143
 
9_
 

+10
144

+11
145

+12
146

+13
147

+14
148

+15
149

+16
150

+17
151

+18
152

+19
153

+1A
154

+1B
155

+1C
156

+1D
157

+1E
158

+1F
159
 
A_
 

+20
160

+21
161

+22
162

+23
163

+24
164

+25
165

+26
166

+27
167

+28
168

+29
169

+2A
170

+2B
171

+2C
172

+2D
173

+2E
174

+2F
175
 
B_
 

+30
176

+31
177

+32
178

+33
179

+34
180

+35
181

+36
182

+37
183

+38
184

+39
185

+3A
186

+3B
187

+3C
188

+3D
189

+3E
190

+3F
191
 
2-byte
C_
 
2-byte
inval

(0000)
192
2-byte
inval

(0040)
193
Latin-1
0080
194
Latin-1
00C0
195
Latin
Ext-A

0100
196
Latin
Ext-A

0140
197
Latin
Ext-B

0180
198
Latin
Ext-B

01C0
199
Latin
Ext-B

0200
200
IPA
0240
201
IPA
0280
202
Spaci
Modif

02C0
203
Combi
Diacr

0300
204
Combi
Diacr

0340
205
Greek
0380
206
Greek
03C0
207
 
2-byte
D_
 
Cyril
0400
208
Cyril
0440
209
Cyril
0480
210
Cyril
04C0
211
Cyril
0500
212
Armen
0540
213
Hebrew
0580
214
Hebrew
05C0
215
Arabic
0600
216
Arabic
0640
217
Arabic
0680
218
Arabic
06C0
219
Syriac
0700
220
Arabic
0740
221
Thaana
0780
222
N'Ko
07C0
223
 
3-byte
E_
 
Indic
0800*
224
Misc.
1000
225
Symbol
2000
226
Kana
CJK

3000
227
CJK
4000
228
CJK
5000
229
CJK
6000
230
CJK
7000
231
CJK
8000
232
CJK
9000
233
Asian
A000
234
Hangul
B000
235
Hangul
C000
236
Hangul
Surr

D000
237
Priv Use
E000
238
Forms
F000
239
 
4-byte
F_
 
Ancient
Sym,CJK

10000*
240
unall
40000
241
unall
80000
242
Tags
Priv

C0000
243
Priv
Use

100000
244
4-byte
inval

140000
245
4-byte
inval

180000
246
4-byte
inval

1C0000
247
5-byte
inval

200000*
248
5-byte
inval

1000000
249
5-byte
inval

2000000
250
5-byte
inval

3000000
251
6-byte
inval

4000000*
252
6-byte
inval

40000000
253


254


255

Legend: Yellow cells are control characters, blue cells are punctuation, purple cells are digits and green cells are ASCII letters.

Orange cells with a large dot are continuation bytes. The hexadecimal number shown after a "+" plus sign is the value of the 6 bits they add.

White cells are the start 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 start byte. When a start byte could form both overlong and valid encodings, the lowest non-overlong-encoded code point is shown, marked by an asterisk "*".

Red cells must never appear in a valid UTF-8 sequence. The first two (C0 and C1) could only be used for overlong encoding of basic ASCII characters (i.e., trying to encode a 7-bit ASCII value between 0 and 127 using 2 bytes instead of 1). The remaining red cells indicate start bytes of sequences that could only encode numbers larger than the 0x10FFFF limit of Unicode. The byte 244 (hex 0xF4) could also encode some values greater than 0x10FFFF; such a sequence would also be invalid if the subsequent bytes attempted to encode a value higher than 0x10FFFF.

Overlong encodings[edit]

In principle, it would be possible to inflate the number of bytes in an encoding by padding the code point with leading 0s. To encode the Euro sign € from the above example in four bytes instead of three, it could be padded with leading 0s until it was 21 bits long—000 000010 000010 101100, and encoded as 11110000 10000010 10000010 10101100 (or F0 82 82 AC in hexadecimal). 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 code 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 a unique valid encoding for each code point, this makes string comparisons and searches well-defined.

Modified UTF-8 uses the 2-byte overlong encoding of U+0000 (the NUL character), 11000000 10000000 (hex C0 80), rather than 00000000 (hex 00). This allows the byte 00 to be used as a string terminator.

Invalid byte sequences[edit]

Not all sequences of bytes are valid UTF-8. A UTF-8 decoder should be prepared for:

Many earlier decoders would happily try to decode these. Carefully crafted invalid UTF-8 could make them either skip or create ASCII characters such as NUL, slash, or quotes. Invalid UTF-8 has been used to bypass security validations in high profile products including Microsoft's IIS web server[12] and Apache's Tomcat servlet container.[13]

RFC 3629 states "Implementations of the decoding algorithm MUST protect against decoding invalid sequences."[14] The Unicode Standard requires decoders to "...treat any ill-formed code unit sequence as an error condition. This guarantees that it will neither interpret nor emit an ill-formed code unit sequence."

Many UTF-8 decoders throw exceptions on encountering errors.[15] This can turn what would otherwise be harmless errors (producing a message such as "no such file") into a denial of service bug. Early versions of Python 3.0 would exit immediately if the command line or environment variables contained invalid UTF-8,[16] making it impossible to handle such errors.

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. Popular replacements include:

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.

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-8859-1. Thus, the software can check for UTF-8 correctness, and if that fails assume the input to be in the legacy encoding. It is technically true that this may detect an ISO-8859-1 string as UTF-8, but this is very unlikely if it contains any 8-bit bytes as they all have to be in unusual patterns of two or more in a row, such as "£".

Invalid code points[edit]

According to the UTF-8 definition (RFC 3629) the high and low surrogate halves used by UTF-16 (U+D800 through U+DFFF) are not legal Unicode values, and their UTF-8 encoding should be treated as an invalid byte sequence.

Whether an actual application should do this is debatable, as it makes it impossible to store invalid UTF-16 (that is, UTF-16 with unpaired surrogate halves) in a UTF-8 string. This is necessary to store unchecked UTF-16 such as Windows filenames as UTF-8. It is also incompatible with CESU encoding (described below).

Sample code[edit]

This code assumes ungetc can be called more than once. It translates any encoding errors into 0xDCxx, where xx is the value of the error byte.

 void write_utf8(unsigned code_point) {   if (code_point < 0x80) {     putchar(code_point);   } else if (code_point <= 0x7FF) {     putchar((code_point >> 6) + 0xC0);     putchar((code_point & 0x3F) + 0x80);   } else if (code_point <= 0xFFFF) {     putchar((code_point >> 12) + 0xE0);     putchar(((code_point >> 6) & 0x3F) + 0x80);     putchar((code_point & 0x3F) + 0x80);   } else if (code_point <= 0x10FFFF) {     putchar((code_point >> 18) + 0xF0);     putchar(((code_point >> 12) & 0x3F) + 0x80);     putchar(((code_point >> 6) & 0x3F) + 0x80);     putchar((code_point & 0x3F) + 0x80);   } else {     error("invalid code_point");   } }   unsigned read_code_point_from_utf8() {   int code_unit1, code_unit2, code_unit3, code_unit4;     code_unit1 = getchar();   if (code_unit1 < 0x80) {     return code_unit1;   } else if (code_unit1 < 0xC2) {     /* continuation or overlong 2-byte sequence */     goto ERROR1;   } else if (code_unit1 < 0xE0) {     /* 2-byte sequence */     code_unit2 = getchar();     if ((code_unit2 & 0xC0) != 0x80) goto ERROR2;     return (code_unit1 << 6) + code_unit2 - 0x3080;   } else if (code_unit1 < 0xF0) {     /* 3-byte sequence */     code_unit2 = getchar();     if ((code_unit2 & 0xC0) != 0x80) goto ERROR2;     if (code_unit1 == 0xE0 && code_unit2 < 0xA0) goto ERROR2; /* overlong */     code_unit3 = getchar();     if ((code_unit3 & 0xC0) != 0x80) goto ERROR3;     return (code_unit1 << 12) + (code_unit2 << 6) + code_unit3 - 0xE2080;   } else if (code_unit1 < 0xF5) {     /* 4-byte sequence */     code_unit2 = getchar();     if ((code_unit2 & 0xC0) != 0x80) goto ERROR2;     if (code_unit1 == 0xF0 && code_unit2 < 0x90) goto ERROR2; /* overlong */     if (code_unit1 == 0xF4 && code_unit2 >= 0x90) goto ERROR2; /* > U+10FFFF */     code_unit3 = getchar();     if ((code_unit3 & 0xC0) != 0x80) goto ERROR3;     code_unit4 = getchar();     if ((code_unit4 & 0xC0) != 0x80) goto ERROR4;     return (code_unit1 << 18) + (code_unit2 << 12) + (code_unit3 << 6) + code_unit4 - 0x3C82080;   } else {     /* > U+10FFFF */     goto ERROR1;   }     ERROR4:     ungetc(code_unit4, stdin);   ERROR3:     ungetc(code_unit3, stdin);   ERROR2:     ungetc(code_unit2, stdin);   ERROR1:     return code_unit1 + 0xDC00; } 

Official name and variants[edit]

The official name is "UTF-8". All letters are upper-case, and the name is hyphenated. This spelling is used in all the Unicode Consortium documents relating to the encoding.

Alternatively, the name "utf-8" may be used by all standards conforming to the Internet Assigned Numbers Authority (IANA) list (which include CSS, HTML, XML, and HTTP headers),[19] as the declaration is case insensitive.[20]

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.[14] Despite this, most agents such as browsers can understand them, and so standards intended to describe existing practice (such as HTML5) may effectively require their recognition.

Unofficially, UTF-8-BOM or UTF-8-NOBOM are sometimes used to refer to text files which contain or lack a byte order mark (BOM). In Japan especially, UTF-8 encoding without BOM is sometimes called "UTF-8N".[21][22]

Derivatives[edit]

The following implementations show slight differences from the UTF-8 specification. They are incompatible with the UTF-8 specification.

CESU-8[edit]

Main article: CESU-8

Many programs added UTF-8 conversions for UCS-2 data and did not alter this UTF-8 conversion when UCS-2 was replaced with the surrogate-pair using UTF-16. In such programs each half of a UTF-16 surrogate pair is encoded as its own 3-byte UTF-8 encoding, resulting in 6-byte sequences rather than 4 bytes for characters outside the Basic Multilingual Plane. Oracle and MySQL databases use this, as well as Java and Tcl as described below, and probably many Windows programs where the programmers were unaware of the complexities of UTF-16. Although this non-optimal encoding is generally not deliberate, a supposed benefit is that it preserves UTF-16 binary sorting order when CESU-8 is binary sorted.

Modified UTF-8[edit]

In Modified UTF-8,[23] the null character (U+0000) is encoded as 0xC0,0x80; this is not valid UTF-8[24] because it is not the shortest possible representation. Modified UTF-8 strings never contain any actual null bytes but can contain all Unicode code points including U+0000,[25] which allows such strings (with a null byte appended) to be processed by traditional null-terminated string functions.

All known Modified UTF-8 implementations also treat the surrogate pairs as in CESU-8.

In normal usage, the Java programming language supports standard UTF-8 when reading and writing strings through InputStreamReader and OutputStreamWriter. However it uses Modified UTF-8 for object serialization,[26] for the Java Native Interface,[27] and for embedding constant strings in class files.[28] The dex format defined by Dalvik also uses the same modified UTF-8 to represent string values.[29] Tcl also uses the same modified UTF-8[30] as Java for internal representation of Unicode data, but uses strict CESU-8 for external data.

Byte order mark[edit]

Many Windows programs (including Windows Notepad) add the bytes 0xEF, 0xBB, 0xBF at the start of any document saved as UTF-8. This is the UTF-8 encoding of the Unicode byte order mark (BOM), and is commonly referred to as a UTF-8 BOM, even though it is not relevant to byte order. A BOM can also appear if another encoding with a BOM is translated to UTF-8 without stripping it. Software that is not aware of multibyte encodings will display the BOM as three strange characters (e.g. "" in software interpreting the document as ISO 8859-1 or Windows-1252) at the start of the document.

The Unicode Standard neither requires nor recommends the use of the BOM for UTF-8.[31] The presence of the UTF-8 BOM may cause interoperability problems with existing software that could otherwise handle UTF-8; for example:

If compatibility with existing programs is not important, the BOM could be used to identify UTF-8 encoding, but such use should not be necessary as UTF-8 can be identified with very high reliability since other encodings are extremely unlikely to contain valid UTF-8 byte sequences.

Advantages and disadvantages[edit]

General[edit]

Advantages[edit]

Disadvantages[edit]

Compared to single-byte encodings[edit]

Advantages[edit]

Disadvantages[edit]

Compared to other multi-byte encodings[edit]

Advantages[edit]

Disadvantages[edit]

Compared to UTF-16[edit]

Advantages[edit]

Disadvantages[edit]

See also[edit]

References[edit]

  1. ^ "Chapter 2. General Structure". The Unicode Standard (6.0 ed.). Mountain View, California, USA: The Unicode Consortium. ISBN 978-1-936213-01-6. 
  2. ^ a b Davis, Mark (28 January 2010). "Unicode nearing 50% of the web". Official Google Blog. Google. Retrieved 5 December 2010. 
  3. ^ "Usage Statistics of Character Encodings for Websites, November 2014". W3Techs. 5 November 2014. Retrieved 5 November 2014. 
  4. ^ "UTF-8 Usage Statistics". BuiltWith. Retrieved March 28, 2011. 
  5. ^ "Using International Characters in Internet Mail". Internet Mail Consortium. August 1, 1998. Retrieved November 8, 2007. 
  6. ^ "CHARACTER SETS". Internet Assigned Numbers Authority. November 4, 2010. Retrieved 5 December 2010. 
  7. ^ a b Pike, Rob (30 Apr 2003). "UTF-8 history". Retrieved September 7, 2012. 
  8. ^ Pike, Rob (September 6, 2012). "UTF-8 turned 20 years old yesterday". Retrieved September 7, 2012. 
  9. ^ Davis, Mark (5 May 2008). "Moving to Unicode 5.1". Retrieved 2013-03-01. 
  10. ^ Goodger, David (6 May 2008). "Unicode misinformation". Retrieved 2013-03-01. 
  11. ^ Allen, Julie D.; Anderson, Deborah; Becker, Joe; Cook, Richard, eds. (2012). "The Unicode Standard, Version 6.1". Mountain View, California: Unicode Consortium. "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." 
  12. ^ Marin, Marvin (October 17, 2000). "Web Server Folder Traversal MS00-078". 
  13. ^ "National Vulnerability Database - Summary for CVE-2008-2938". 
  14. ^ a b c Yergeau, F. (2003). "UTF-8, a transformation format of ISO 10646". "RFC 3629". Internet Engineering Task Force. 
  15. ^ decode() method of Java UTF8 object
  16. ^ "Non-decodable Bytes in System Character Interfaces". python.org. 2009-04-22. Retrieved 2014-08-13. 
  17. ^ Kuhn, Markus (2000-07-23). "Substituting malformed UTF-8 sequences in a decoder". Retrieved 2014-09-25. 
  18. ^ Sittler, B. (2006-04-02). "Binary vs. UTF-8, and why it need not matter". Retrieved 2014-09-25. 
  19. ^ Dürst, Martin. "Setting the HTTP charset parameter". W3C. Retrieved February 8, 2013. 
  20. ^ "Character Sets". Internet Assigned Numbers Authority. January 23, 2013. Retrieved February 8, 2013. 
  21. ^ "BOM - suikawiki" (in Japanese). Retrieved 2013-04-26. 
  22. ^ Mark Davis. "Forms of Unicode". IBM. Archived from the original on 6 May 2005. Retrieved 18 September 2013. 
  23. ^ "Java SE 6 documentation for Interface java.io.DataInput, subsection on Modified UTF-8". Sun Microsystems. 2008. Retrieved May 22, 2009. 
  24. ^ "Request for Comments 3629: "UTF-8, a transformation format of ISO 10646"". 2003. Retrieved May 22, 2009. "[...] the overlong UTF-8 sequence C0 80 [...]", "[...] the illegal two-octet sequence C0 80 [...]" 
  25. ^ "The Java Virtual Machine Specification, 2nd Edition, section 4.4.7: "The CONSTANT_Utf8_info Structure"". Sun Microsystems. 1999. Retrieved May 24, 2009. "[...] Java virtual machine UTF-8 strings never have embedded nulls." 
  26. ^ "Java Object Serialization Specification, chapter 6: Object Serialization Stream Protocol, section 2: Stream Elements". Sun Microsystems. 2005. Retrieved May 22, 2009. "[...] encoded in modified UTF-8." 
  27. ^ "Java Native Interface Specification, chapter 3: JNI Types and Data Structures, section: Modified UTF-8 Strings". Sun Microsystems. 2003. Retrieved May 22, 2009. "The JNI uses modified UTF-8 strings to represent various string types." 
  28. ^ "The Java Virtual Machine Specification, 2nd Edition, section 4.4.7: "The CONSTANT_Utf8_info Structure"". Sun Microsystems. 1999. Retrieved May 23, 2009. "[...] differences between this format and the "standard" UTF-8 format." 
  29. ^ "dex — Dalvik Executable Format". Retrieved April 9, 2013. "[T]he dex format encodes its string data in a de facto standard modified UTF-8 form, hereafter referred to as MUTF-8." 
  30. ^ "Tcler's Wiki: UTF-8 bit by bit (Revision 6)". April 25, 2009. Retrieved May 22, 2009. "In orthodox UTF-8, a NUL byte(\x00) is represented by a NUL byte. [...] But [...] we [...] want NUL bytes inside [...] strings [...]" 
  31. ^ "The Unicode Standard - Chapter 2". p. 30. 
  32. ^ "Extensible Markup Language (XML) 1.0 (Fifth Edition)". W3C. November 26, 2008. Retrieved February 8, 2013. 
  33. ^ Dürst, Martin. "Multilingual Forms". W3C. Retrieved February 8, 2013. 
  34. ^ There are 256 × 256 − 128 × 128 = 49152 2-byte sequences with at least one high bit set, only 1920 encode valid UTF-8 characters (the range U+0080 to U+07FF), 1920 ÷ 49152 = 3.9%
  35. ^ "#418058 - iconv: half-smart on ascii compatible code conversion (shift-jis) - Debian Bug report logs". Bugs.debian.org. 2007-04-06. Retrieved 2014-06-13. 
  36. ^ Although the difference may not be great: the 2010-11-22 version of hi:यूनिकोड (Unicode in Hindi), when the pure text was pasted to Notepad, generated 19 KB when saved as UTF-16 and 22 KB when saved as UTF-8.
  37. ^ The 2010-10-27 version of ja:UTF-8 generated 169 KB when converted with Notepad to UTF-16, and only 101 KB when converted back to UTF-8. The 2010-11-22 version of hi:यूनिकोड (Unicode in Hindi) required 119 KB in UTF-16 and 76 KB in UTF-8.

External links[edit]

There are several current definitions of UTF-8 in various standards documents:

They supersede the definitions given in the following obsolete works:

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.