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1 <html>
2 <head>
3 <title>pcreunicode specification</title>
4 </head>
5 <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6 <h1>pcreunicode man page</h1>
7 <p>
8 Return to the <a href="index.html">PCRE index page</a>.
9 </p>
10 <p>
11 This page is part of the PCRE HTML documentation. It was generated automatically
12 from the original man page. If there is any nonsense in it, please consult the
13 man page, in case the conversion went wrong.
14 <br>
15 <br><b>
16 UTF-8, UTF-16, AND UNICODE PROPERTY SUPPORT
17 </b><br>
18 <P>
19 From Release 8.30, in addition to its previous UTF-8 support, PCRE also
20 supports UTF-16 by means of a separate 16-bit library. This can be built as
21 well as, or instead of, the 8-bit library.
22 </P>
23 <br><b>
24 UTF-8 SUPPORT
25 </b><br>
26 <P>
27 In order process UTF-8 strings, you must build PCRE's 8-bit library with UTF
28 support, and, in addition, you must call
29 <a href="pcre_compile.html"><b>pcre_compile()</b></a>
30 with the PCRE_UTF8 option flag, or the pattern must start with the sequence
31 (*UTF8). When either of these is the case, both the pattern and any subject
32 strings that are matched against it are treated as UTF-8 strings instead of
33 strings of 1-byte characters.
34 </P>
35 <br><b>
36 UTF-16 SUPPORT
37 </b><br>
38 <P>
39 In order process UTF-16 strings, you must build PCRE's 16-bit library with UTF
40 support, and, in addition, you must call
41 <a href="pcre_compile.html"><b>pcre16_compile()</b></a>
42 with the PCRE_UTF16 option flag, or the pattern must start with the sequence
43 (*UTF16). When either of these is the case, both the pattern and any subject
44 strings that are matched against it are treated as UTF-16 strings instead of
45 strings of 16-bit characters.
46 </P>
47 <br><b>
48 UTF SUPPORT OVERHEAD
49 </b><br>
50 <P>
51 If you compile PCRE with UTF support, but do not use it at run time, the
52 library will be a bit bigger, but the additional run time overhead is limited
53 to testing the PCRE_UTF8/16 flag occasionally, so should not be very big.
54 </P>
55 <br><b>
56 UNICODE PROPERTY SUPPORT
57 </b><br>
58 <P>
59 If PCRE is built with Unicode character property support (which implies UTF
60 support), the escape sequences \p{..}, \P{..}, and \X can be used.
61 The available properties that can be tested are limited to the general
62 category properties such as Lu for an upper case letter or Nd for a decimal
63 number, the Unicode script names such as Arabic or Han, and the derived
64 properties Any and L&. A full list is given in the
65 <a href="pcrepattern.html"><b>pcrepattern</b></a>
66 documentation. Only the short names for properties are supported. For example,
67 \p{L} matches a letter. Its Perl synonym, \p{Letter}, is not supported.
68 Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
69 compatibility with Perl 5.6. PCRE does not support this.
70 <a name="utf8strings"></a></P>
71 <br><b>
72 Validity of UTF-8 strings
73 </b><br>
74 <P>
75 When you set the PCRE_UTF8 flag, the byte strings passed as patterns and
76 subjects are (by default) checked for validity on entry to the relevant
77 functions. The entire string is checked before any other processing takes
78 place. From release 7.3 of PCRE, the check is according the rules of RFC 3629,
79 which are themselves derived from the Unicode specification. Earlier releases
80 of PCRE followed the rules of RFC 2279, which allows the full range of 31-bit
81 values (0 to 0x7FFFFFFF). The current check allows only values in the range U+0
82 to U+10FFFF, excluding U+D800 to U+DFFF.
83 </P>
84 <P>
85 The excluded code points are the "Surrogate Area" of Unicode. They are reserved
86 for use by UTF-16, where they are used in pairs to encode codepoints with
87 values greater than 0xFFFF. The code points that are encoded by UTF-16 pairs
88 are available independently in the UTF-8 encoding. (In other words, the whole
89 surrogate thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
90 </P>
91 <P>
92 If an invalid UTF-8 string is passed to PCRE, an error return is given. At
93 compile time, the only additional information is the offset to the first byte
94 of the failing character. The run-time functions <b>pcre_exec()</b> and
95 <b>pcre_dfa_exec()</b> also pass back this information, as well as a more
96 detailed reason code if the caller has provided memory in which to do this.
97 </P>
98 <P>
99 In some situations, you may already know that your strings are valid, and
100 therefore want to skip these checks in order to improve performance, for
101 example in the case of a long subject string that is being scanned repeatedly
102 with different patterns. If you set the PCRE_NO_UTF8_CHECK flag at compile time
103 or at run time, PCRE assumes that the pattern or subject it is given
104 (respectively) contains only valid UTF-8 codes. In this case, it does not
105 diagnose an invalid UTF-8 string.
106 </P>
107 <P>
108 If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, what
109 happens depends on why the string is invalid. If the string conforms to the
110 "old" definition of UTF-8 (RFC 2279), it is processed as a string of characters
111 in the range 0 to 0x7FFFFFFF by <b>pcre_dfa_exec()</b> and the interpreted
112 version of <b>pcre_exec()</b>. In other words, apart from the initial validity
113 test, these functions (when in UTF-8 mode) handle strings according to the more
114 liberal rules of RFC 2279. However, the just-in-time (JIT) optimization for
115 <b>pcre_exec()</b> supports only RFC 3629. If you are using JIT optimization, or
116 if the string does not even conform to RFC 2279, the result is undefined. Your
117 program may crash.
118 </P>
119 <P>
120 If you want to process strings of values in the full range 0 to 0x7FFFFFFF,
121 encoded in a UTF-8-like manner as per the old RFC, you can set
122 PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in this
123 situation, you will have to apply your own validity check, and avoid the use of
124 JIT optimization.
125 <a name="utf16strings"></a></P>
126 <br><b>
127 Validity of UTF-16 strings
128 </b><br>
129 <P>
130 When you set the PCRE_UTF16 flag, the strings of 16-bit data units that are
131 passed as patterns and subjects are (by default) checked for validity on entry
132 to the relevant functions. Values other than those in the surrogate range
133 U+D800 to U+DFFF are independent code points. Values in the surrogate range
134 must be used in pairs in the correct manner.
135 </P>
136 <P>
137 If an invalid UTF-16 string is passed to PCRE, an error return is given. At
138 compile time, the only additional information is the offset to the first data
139 unit of the failing character. The run-time functions <b>pcre16_exec()</b> and
140 <b>pcre16_dfa_exec()</b> also pass back this information, as well as a more
141 detailed reason code if the caller has provided memory in which to do this.
142 </P>
143 <P>
144 In some situations, you may already know that your strings are valid, and
145 therefore want to skip these checks in order to improve performance. If you set
146 the PCRE_NO_UTF16_CHECK flag at compile time or at run time, PCRE assumes that
147 the pattern or subject it is given (respectively) contains only valid UTF-16
148 sequences. In this case, it does not diagnose an invalid UTF-16 string.
149 </P>
150 <br><b>
151 General comments about UTF modes
152 </b><br>
153 <P>
154 1. Codepoints less than 256 can be specified by either braced or unbraced
155 hexadecimal escape sequences (for example, \x{b3} or \xb3). Larger values
156 have to use braced sequences.
157 </P>
158 <P>
159 2. Octal numbers up to \777 are recognized, and in UTF-8 mode, they match
160 two-byte characters for values greater than \177.
161 </P>
162 <P>
163 3. Repeat quantifiers apply to complete UTF characters, not to individual
164 data units, for example: \x{100}{3}.
165 </P>
166 <P>
167 4. The dot metacharacter matches one UTF character instead of a single data
168 unit.
169 </P>
170 <P>
171 5. The escape sequence \C can be used to match a single byte in UTF-8 mode, or
172 a single 16-bit data unit in UTF-16 mode, but its use can lead to some strange
173 effects because it breaks up multi-unit characters (see the description of \C
174 in the
175 <a href="pcrepattern.html"><b>pcrepattern</b></a>
176 documentation). The use of \C is not supported in the alternative matching
177 function <b>pcre[16]_dfa_exec()</b>, nor is it supported in UTF mode by the JIT
178 optimization of <b>pcre[16]_exec()</b>. If JIT optimization is requested for a
179 UTF pattern that contains \C, it will not succeed, and so the matching will
180 be carried out by the normal interpretive function.
181 </P>
182 <P>
183 6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
184 test characters of any code value, but, by default, the characters that PCRE
185 recognizes as digits, spaces, or word characters remain the same set as in
186 non-UTF mode, all with values less than 256. This remains true even when PCRE
187 is built to include Unicode property support, because to do otherwise would
188 slow down PCRE in many common cases. Note in particular that this applies to
189 \b and \B, because they are defined in terms of \w and \W. If you really
190 want to test for a wider sense of, say, "digit", you can use explicit Unicode
191 property tests such as \p{Nd}. Alternatively, if you set the PCRE_UCP option,
192 the way that the character escapes work is changed so that Unicode properties
193 are used to determine which characters match. There are more details in the
194 section on
195 <a href="pcrepattern.html#genericchartypes">generic character types</a>
196 in the
197 <a href="pcrepattern.html"><b>pcrepattern</b></a>
198 documentation.
199 </P>
200 <P>
201 7. Similarly, characters that match the POSIX named character classes are all
202 low-valued characters, unless the PCRE_UCP option is set.
203 </P>
204 <P>
205 8. However, the horizontal and vertical white space matching escapes (\h, \H,
206 \v, and \V) do match all the appropriate Unicode characters, whether or not
207 PCRE_UCP is set.
208 </P>
209 <P>
210 9. Case-insensitive matching applies only to characters whose values are less
211 than 128, unless PCRE is built with Unicode property support. Even when Unicode
212 property support is available, PCRE still uses its own character tables when
213 checking the case of low-valued characters, so as not to degrade performance.
214 The Unicode property information is used only for characters with higher
215 values. Furthermore, PCRE supports case-insensitive matching only when there is
216 a one-to-one mapping between a letter's cases. There are a small number of
217 many-to-one mappings in Unicode; these are not supported by PCRE.
218 </P>
219 <br><b>
220 AUTHOR
221 </b><br>
222 <P>
223 Philip Hazel
224 <br>
225 University Computing Service
226 <br>
227 Cambridge CB2 3QH, England.
228 <br>
229 </P>
230 <br><b>
231 REVISION
232 </b><br>
233 <P>
234 Last updated: 14 April 2012
235 <br>
236 Copyright &copy; 1997-2012 University of Cambridge.
237 <br>
238 <p>
239 Return to the <a href="index.html">PCRE index page</a>.
240 </p>

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