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Fix COMMIT in recursion; document backtracking verbs in assertions and 
subroutines.
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, UTF-32, AND UNICODE PROPERTY SUPPORT
17 </b><br>
18 <P>
19 As well as UTF-8 support, PCRE also supports UTF-16 (from release 8.30) and
20 UTF-32 (from release 8.32), by means of two additional libraries. They can be
21 built as 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) or (*UTF). When either of these is the case, both the pattern and any
32 subject strings that are matched against it are treated as UTF-8 strings
33 instead of strings of individual 1-byte characters.
34 </P>
35 <br><b>
36 UTF-16 AND UTF-32 SUPPORT
37 </b><br>
38 <P>
39 In order process UTF-16 or UTF-32 strings, you must build PCRE's 16-bit or
40 32-bit library with UTF support, and, in addition, you must call
41 <a href="pcre16_compile.html"><b>pcre16_compile()</b></a>
42 or
43 <a href="pcre32_compile.html"><b>pcre32_compile()</b></a>
44 with the PCRE_UTF16 or PCRE_UTF32 option flag, as appropriate. Alternatively,
45 the pattern must start with the sequence (*UTF16), (*UTF32), as appropriate, or
46 (*UTF), which can be used with either library. When UTF mode is set, both the
47 pattern and any subject strings that are matched against it are treated as
48 UTF-16 or UTF-32 strings instead of strings of individual 16-bit or 32-bit
49 characters.
50 </P>
51 <br><b>
52 UTF SUPPORT OVERHEAD
53 </b><br>
54 <P>
55 If you compile PCRE with UTF support, but do not use it at run time, the
56 library will be a bit bigger, but the additional run time overhead is limited
57 to testing the PCRE_UTF[8|16|32] flag occasionally, so should not be very big.
58 </P>
59 <br><b>
60 UNICODE PROPERTY SUPPORT
61 </b><br>
62 <P>
63 If PCRE is built with Unicode character property support (which implies UTF
64 support), the escape sequences \p{..}, \P{..}, and \X can be used.
65 The available properties that can be tested are limited to the general
66 category properties such as Lu for an upper case letter or Nd for a decimal
67 number, the Unicode script names such as Arabic or Han, and the derived
68 properties Any and L&. Full lists is given in the
69 <a href="pcrepattern.html"><b>pcrepattern</b></a>
70 and
71 <a href="pcresyntax.html"><b>pcresyntax</b></a>
72 documentation. Only the short names for properties are supported. For example,
73 \p{L} matches a letter. Its Perl synonym, \p{Letter}, is not supported.
74 Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
75 compatibility with Perl 5.6. PCRE does not support this.
76 <a name="utf8strings"></a></P>
77 <br><b>
78 Validity of UTF-8 strings
79 </b><br>
80 <P>
81 When you set the PCRE_UTF8 flag, the byte strings passed as patterns and
82 subjects are (by default) checked for validity on entry to the relevant
83 functions. The entire string is checked before any other processing takes
84 place. From release 7.3 of PCRE, the check is according the rules of RFC 3629,
85 which are themselves derived from the Unicode specification. Earlier releases
86 of PCRE followed the rules of RFC 2279, which allows the full range of 31-bit
87 values (0 to 0x7FFFFFFF). The current check allows only values in the range U+0
88 to U+10FFFF, excluding the surrogate area. (From release 8.33 the so-called
89 "non-character" code points are no longer excluded because Unicode corrigendum
90 #9 makes it clear that they should not be.)
91 </P>
92 <P>
93 Characters in the "Surrogate Area" of Unicode are reserved for use by UTF-16,
94 where they are used in pairs to encode codepoints with values greater than
95 0xFFFF. The code points that are encoded by UTF-16 pairs are available
96 independently in the UTF-8 and UTF-32 encodings. (In other words, the whole
97 surrogate thing is a fudge for UTF-16 which unfortunately messes up UTF-8 and
98 UTF-32.)
99 </P>
100 <P>
101 If an invalid UTF-8 string is passed to PCRE, an error return is given. At
102 compile time, the only additional information is the offset to the first byte
103 of the failing character. The run-time functions <b>pcre_exec()</b> and
104 <b>pcre_dfa_exec()</b> also pass back this information, as well as a more
105 detailed reason code if the caller has provided memory in which to do this.
106 </P>
107 <P>
108 In some situations, you may already know that your strings are valid, and
109 therefore want to skip these checks in order to improve performance, for
110 example in the case of a long subject string that is being scanned repeatedly.
111 If you set the PCRE_NO_UTF8_CHECK flag at compile time or at run time, PCRE
112 assumes that the pattern or subject it is given (respectively) contains only
113 valid UTF-8 codes. In this case, it does not diagnose an invalid UTF-8 string.
114 </P>
115 <P>
116 Note that passing PCRE_NO_UTF8_CHECK to <b>pcre_compile()</b> just disables the
117 check for the pattern; it does not also apply to subject strings. If you want
118 to disable the check for a subject string you must pass this option to
119 <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>.
120 </P>
121 <P>
122 If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, the result
123 is undefined and your program may crash.
124 <a name="utf16strings"></a></P>
125 <br><b>
126 Validity of UTF-16 strings
127 </b><br>
128 <P>
129 When you set the PCRE_UTF16 flag, the strings of 16-bit data units that are
130 passed as patterns and subjects are (by default) checked for validity on entry
131 to the relevant functions. Values other than those in the surrogate range
132 U+D800 to U+DFFF are independent code points. Values in the surrogate range
133 must be used in pairs in the correct manner.
134 </P>
135 <P>
136 If an invalid UTF-16 string is passed to PCRE, an error return is given. At
137 compile time, the only additional information is the offset to the first data
138 unit of the failing character. The run-time functions <b>pcre16_exec()</b> and
139 <b>pcre16_dfa_exec()</b> also pass back this information, as well as a more
140 detailed reason code if the caller has provided memory in which to do this.
141 </P>
142 <P>
143 In some situations, you may already know that your strings are valid, and
144 therefore want to skip these checks in order to improve performance. If you set
145 the PCRE_NO_UTF16_CHECK flag at compile time or at run time, PCRE assumes that
146 the pattern or subject it is given (respectively) contains only valid UTF-16
147 sequences. In this case, it does not diagnose an invalid UTF-16 string.
148 However, if an invalid string is passed, the result is undefined.
149 <a name="utf32strings"></a></P>
150 <br><b>
151 Validity of UTF-32 strings
152 </b><br>
153 <P>
154 When you set the PCRE_UTF32 flag, the strings of 32-bit data units that are
155 passed as patterns and subjects are (by default) checked for validity on entry
156 to the relevant functions. This check allows only values in the range U+0
157 to U+10FFFF, excluding the surrogate area U+D800 to U+DFFF.
158 </P>
159 <P>
160 If an invalid UTF-32 string is passed to PCRE, an error return is given. At
161 compile time, the only additional information is the offset to the first data
162 unit of the failing character. The run-time functions <b>pcre32_exec()</b> and
163 <b>pcre32_dfa_exec()</b> also pass back this information, as well as a more
164 detailed reason code if the caller has provided memory in which to do this.
165 </P>
166 <P>
167 In some situations, you may already know that your strings are valid, and
168 therefore want to skip these checks in order to improve performance. If you set
169 the PCRE_NO_UTF32_CHECK flag at compile time or at run time, PCRE assumes that
170 the pattern or subject it is given (respectively) contains only valid UTF-32
171 sequences. In this case, it does not diagnose an invalid UTF-32 string.
172 However, if an invalid string is passed, the result is undefined.
173 </P>
174 <br><b>
175 General comments about UTF modes
176 </b><br>
177 <P>
178 1. Codepoints less than 256 can be specified in patterns by either braced or
179 unbraced hexadecimal escape sequences (for example, \x{b3} or \xb3). Larger
180 values have to use braced sequences.
181 </P>
182 <P>
183 2. Octal numbers up to \777 are recognized, and in UTF-8 mode they match
184 two-byte characters for values greater than \177.
185 </P>
186 <P>
187 3. Repeat quantifiers apply to complete UTF characters, not to individual
188 data units, for example: \x{100}{3}.
189 </P>
190 <P>
191 4. The dot metacharacter matches one UTF character instead of a single data
192 unit.
193 </P>
194 <P>
195 5. The escape sequence \C can be used to match a single byte in UTF-8 mode, or
196 a single 16-bit data unit in UTF-16 mode, or a single 32-bit data unit in
197 UTF-32 mode, but its use can lead to some strange effects because it breaks up
198 multi-unit characters (see the description of \C in the
199 <a href="pcrepattern.html"><b>pcrepattern</b></a>
200 documentation). The use of \C is not supported in the alternative matching
201 function <b>pcre[16|32]_dfa_exec()</b>, nor is it supported in UTF mode by the
202 JIT optimization of <b>pcre[16|32]_exec()</b>. If JIT optimization is requested
203 for a UTF pattern that contains \C, it will not succeed, and so the matching
204 will be carried out by the normal interpretive function.
205 </P>
206 <P>
207 6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
208 test characters of any code value, but, by default, the characters that PCRE
209 recognizes as digits, spaces, or word characters remain the same set as in
210 non-UTF mode, all with values less than 256. This remains true even when PCRE
211 is built to include Unicode property support, because to do otherwise would
212 slow down PCRE in many common cases. Note in particular that this applies to
213 \b and \B, because they are defined in terms of \w and \W. If you really
214 want to test for a wider sense of, say, "digit", you can use explicit Unicode
215 property tests such as \p{Nd}. Alternatively, if you set the PCRE_UCP option,
216 the way that the character escapes work is changed so that Unicode properties
217 are used to determine which characters match. There are more details in the
218 section on
219 <a href="pcrepattern.html#genericchartypes">generic character types</a>
220 in the
221 <a href="pcrepattern.html"><b>pcrepattern</b></a>
222 documentation.
223 </P>
224 <P>
225 7. Similarly, characters that match the POSIX named character classes are all
226 low-valued characters, unless the PCRE_UCP option is set.
227 </P>
228 <P>
229 8. However, the horizontal and vertical white space matching escapes (\h, \H,
230 \v, and \V) do match all the appropriate Unicode characters, whether or not
231 PCRE_UCP is set.
232 </P>
233 <P>
234 9. Case-insensitive matching applies only to characters whose values are less
235 than 128, unless PCRE is built with Unicode property support. A few Unicode
236 characters such as Greek sigma have more than two codepoints that are
237 case-equivalent. Up to and including PCRE release 8.31, only one-to-one case
238 mappings were supported, but later releases (with Unicode property support) do
239 treat as case-equivalent all versions of characters such as Greek sigma.
240 </P>
241 <br><b>
242 AUTHOR
243 </b><br>
244 <P>
245 Philip Hazel
246 <br>
247 University Computing Service
248 <br>
249 Cambridge CB2 3QH, England.
250 <br>
251 </P>
252 <br><b>
253 REVISION
254 </b><br>
255 <P>
256 Last updated: 27 February 2013
257 <br>
258 Copyright &copy; 1997-2013 University of Cambridge.
259 <br>
260 <p>
261 Return to the <a href="index.html">PCRE index page</a>.
262 </p>

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