1PCREUNICODE(3) Library Functions Manual PCREUNICODE(3)
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6 PCRE - Perl-compatible regular expressions
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9 As well as UTF-8 support, PCRE also supports UTF-16 (from release 8.30)
11 and UTF-32 (from release 8.32), by means of two additional libraries.
12 They can be built as well as, or instead of, the 8-bit library.
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15 In order process UTF-8 strings, you must build PCRE's 8-bit library
17 with UTF support, and, in addition, you must call pcre_compile() with
18 the PCRE_UTF8 option flag, or the pattern must start with the sequence
19 (*UTF8) or (*UTF). When either of these is the case, both the pattern
20 and any subject strings that are matched against it are treated as
21 UTF-8 strings instead of strings of individual 1-byte characters.
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24 In order process UTF-16 or UTF-32 strings, you must build PCRE's 16-bit
26 or 32-bit library with UTF support, and, in addition, you must call
27 pcre16_compile() or pcre32_compile() with the PCRE_UTF16 or PCRE_UTF32
28 option flag, as appropriate. Alternatively, the pattern must start with
29 the sequence (*UTF16), (*UTF32), as appropriate, or (*UTF), which can
30 be used with either library. When UTF mode is set, both the pattern and
31 any subject strings that are matched against it are treated as UTF-16
32 or UTF-32 strings instead of strings of individual 16-bit or 32-bit
33 characters.
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36 If you compile PCRE with UTF support, but do not use it at run time,
38 the library will be a bit bigger, but the additional run time overhead
39 is limited to testing the PCRE_UTF[8|16|32] flag occasionally, so
40 should not be very big.
41
43 If PCRE is built with Unicode character property support (which implies
45 UTF support), the escape sequences \p{..}, \P{..}, and \X can be used.
46 The available properties that can be tested are limited to the general
47 category properties such as Lu for an upper case letter or Nd for a
48 decimal number, the Unicode script names such as Arabic or Han, and the
49 derived properties Any and L&. Full lists is given in the pcrepattern
50 and pcresyntax documentation. Only the short names for properties are
51 supported. For example, \p{L} matches a letter. Its Perl synonym,
52 \p{Letter}, is not supported. Furthermore, in Perl, many properties
53 may optionally be prefixed by "Is", for compatibility with Perl 5.6.
54 PCRE does not support this.
55 Validity of UTF-8 strings
57 When you set the PCRE_UTF8 flag, the byte strings passed as patterns
59 and subjects are (by default) checked for validity on entry to the rel‐
60 evant functions. The entire string is checked before any other process‐
61 ing takes place. From release 7.3 of PCRE, the check is according the
62 rules of RFC 3629, which are themselves derived from the Unicode speci‐
63 fication. Earlier releases of PCRE followed the rules of RFC 2279,
64 which allows the full range of 31-bit values (0 to 0x7FFFFFFF). The
65 current check allows only values in the range U+0 to U+10FFFF, exclud‐
66 ing the surrogate area and the non-characters.
67 Characters in the "Surrogate Area" of Unicode are reserved for use by
69 UTF-16, where they are used in pairs to encode codepoints with values
70 greater than 0xFFFF. The code points that are encoded by UTF-16 pairs
71 are available independently in the UTF-8 and UTF-32 encodings. (In
72 other words, the whole surrogate thing is a fudge for UTF-16 which
73 unfortunately messes up UTF-8 and UTF-32.)
74 Also excluded are the "Non-Character" code points, which are U+FDD0 to
76 U+FDEF and the last two code points in each plane, U+??FFFE and
77 U+??FFFF.
78 If an invalid UTF-8 string is passed to PCRE, an error return is given.
80 At compile time, the only additional information is the offset to the
81 first byte of the failing character. The run-time functions pcre_exec()
82 and pcre_dfa_exec() also pass back this information, as well as a more
83 detailed reason code if the caller has provided memory in which to do
84 this.
85 In some situations, you may already know that your strings are valid,
87 and therefore want to skip these checks in order to improve perfor‐
88 mance, for example in the case of a long subject string that is being
89 scanned repeatedly. If you set the PCRE_NO_UTF8_CHECK flag at compile
90 time or at run time, PCRE assumes that the pattern or subject it is
91 given (respectively) contains only valid UTF-8 codes. In this case, it
92 does not diagnose an invalid UTF-8 string.
93 Note that passing PCRE_NO_UTF8_CHECK to pcre_compile() just disables
95 the check for the pattern; it does not also apply to subject strings.
96 If you want to disable the check for a subject string you must pass
97 this option to pcre_exec() or pcre_dfa_exec().
98 If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, the
100 result is undefined and your program may crash.
101 Validity of UTF-16 strings
103 When you set the PCRE_UTF16 flag, the strings of 16-bit data units that
105 are passed as patterns and subjects are (by default) checked for valid‐
106 ity on entry to the relevant functions. Values other than those in the
107 surrogate range U+D800 to U+DFFF are independent code points. Values in
108 the surrogate range must be used in pairs in the correct manner.
109 Excluded are the "Non-Character" code points, which are U+FDD0 to
111 U+FDEF and the last two code points in each plane, U+??FFFE and
112 U+??FFFF.
113 If an invalid UTF-16 string is passed to PCRE, an error return is
115 given. At compile time, the only additional information is the offset
116 to the first data unit of the failing character. The run-time functions
117 pcre16_exec() and pcre16_dfa_exec() also pass back this information, as
118 well as a more detailed reason code if the caller has provided memory
119 in which to do this.
120 In some situations, you may already know that your strings are valid,
122 and therefore want to skip these checks in order to improve perfor‐
123 mance. If you set the PCRE_NO_UTF16_CHECK flag at compile time or at
124 run time, PCRE assumes that the pattern or subject it is given (respec‐
125 tively) contains only valid UTF-16 sequences. In this case, it does not
126 diagnose an invalid UTF-16 string. However, if an invalid string is
127 passed, the result is undefined.
128 Validity of UTF-32 strings
130 When you set the PCRE_UTF32 flag, the strings of 32-bit data units that
132 are passed as patterns and subjects are (by default) checked for valid‐
133 ity on entry to the relevant functions. This check allows only values
134 in the range U+0 to U+10FFFF, excluding the surrogate area U+D800 to
135 U+DFFF, and the "Non-Character" code points, which are U+FDD0 to U+FDEF
136 and the last two characters in each plane, U+??FFFE and U+??FFFF.
137 If an invalid UTF-32 string is passed to PCRE, an error return is
139 given. At compile time, the only additional information is the offset
140 to the first data unit of the failing character. The run-time functions
141 pcre32_exec() and pcre32_dfa_exec() also pass back this information, as
142 well as a more detailed reason code if the caller has provided memory
143 in which to do this.
144 In some situations, you may already know that your strings are valid,
146 and therefore want to skip these checks in order to improve perfor‐
147 mance. If you set the PCRE_NO_UTF32_CHECK flag at compile time or at
148 run time, PCRE assumes that the pattern or subject it is given (respec‐
149 tively) contains only valid UTF-32 sequences. In this case, it does not
150 diagnose an invalid UTF-32 string. However, if an invalid string is
151 passed, the result is undefined.
152 General comments about UTF modes
154 1. Codepoints less than 256 can be specified in patterns by either
156 braced or unbraced hexadecimal escape sequences (for example, \x{b3} or
157 \xb3). Larger values have to use braced sequences.
158 2. Octal numbers up to \777 are recognized, and in UTF-8 mode they
160 match two-byte characters for values greater than \177.
161 3. Repeat quantifiers apply to complete UTF characters, not to individ‐
163 ual data units, for example: \x{100}{3}.
164 4. The dot metacharacter matches one UTF character instead of a single
166 data unit.
167 5. The escape sequence \C can be used to match a single byte in UTF-8
169 mode, or a single 16-bit data unit in UTF-16 mode, or a single 32-bit
170 data unit in UTF-32 mode, but its use can lead to some strange effects
171 because it breaks up multi-unit characters (see the description of \C
172 in the pcrepattern documentation). The use of \C is not supported in
173 the alternative matching function pcre[16|32]_dfa_exec(), nor is it
174 supported in UTF mode by the JIT optimization of pcre[16|32]_exec(). If
175 JIT optimization is requested for a UTF pattern that contains \C, it
176 will not succeed, and so the matching will be carried out by the normal
177 interpretive function.
178 6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
180 test characters of any code value, but, by default, the characters that
181 PCRE recognizes as digits, spaces, or word characters remain the same
182 set as in non-UTF mode, all with values less than 256. This remains
183 true even when PCRE is built to include Unicode property support,
184 because to do otherwise would slow down PCRE in many common cases. Note
185 in particular that this applies to \b and \B, because they are defined
186 in terms of \w and \W. If you really want to test for a wider sense of,
187 say, "digit", you can use explicit Unicode property tests such as
188 \p{Nd}. Alternatively, if you set the PCRE_UCP option, the way that the
189 character escapes work is changed so that Unicode properties are used
190 to determine which characters match. There are more details in the sec‐
191 tion on generic character types in the pcrepattern documentation.
192 7. Similarly, characters that match the POSIX named character classes
194 are all low-valued characters, unless the PCRE_UCP option is set.
195 8. However, the horizontal and vertical white space matching escapes
197 (\h, \H, \v, and \V) do match all the appropriate Unicode characters,
198 whether or not PCRE_UCP is set.
199 9. Case-insensitive matching applies only to characters whose values
201 are less than 128, unless PCRE is built with Unicode property support.
202 A few Unicode characters such as Greek sigma have more than two code‐
203 points that are case-equivalent. Up to and including PCRE release 8.31,
204 only one-to-one case mappings were supported, but later releases (with
205 Unicode property support) do treat as case-equivalent all versions of
206 characters such as Greek sigma.
207
209 Philip Hazel
211 University Computing Service
212 Cambridge CB2 3QH, England.
213
215 Last updated: 11 November 2012
217 Copyright (c) 1997-2012 University of Cambridge.
218PCRE 8.32 11 November 2012 PCREUNICODE(3)