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.
13
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.
22
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.
34
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. (From release 8.33 the so-called "non-charac‐
67 ter" code points are no longer excluded because Unicode corrigendum #9
68 makes it clear that they should not be.)
69 Characters in the "Surrogate Area" of Unicode are reserved for use by
71 UTF-16, where they are used in pairs to encode codepoints with values
72 greater than 0xFFFF. The code points that are encoded by UTF-16 pairs
73 are available independently in the UTF-8 and UTF-32 encodings. (In
74 other words, the whole surrogate thing is a fudge for UTF-16 which
75 unfortunately messes up UTF-8 and UTF-32.)
76 If an invalid UTF-8 string is passed to PCRE, an error return is given.
78 At compile time, the only additional information is the offset to the
79 first byte of the failing character. The run-time functions pcre_exec()
80 and pcre_dfa_exec() also pass back this information, as well as a more
81 detailed reason code if the caller has provided memory in which to do
82 this.
83 In some situations, you may already know that your strings are valid,
85 and therefore want to skip these checks in order to improve perfor‐
86 mance, for example in the case of a long subject string that is being
87 scanned repeatedly. If you set the PCRE_NO_UTF8_CHECK flag at compile
88 time or at run time, PCRE assumes that the pattern or subject it is
89 given (respectively) contains only valid UTF-8 codes. In this case, it
90 does not diagnose an invalid UTF-8 string.
91 Note that passing PCRE_NO_UTF8_CHECK to pcre_compile() just disables
93 the check for the pattern; it does not also apply to subject strings.
94 If you want to disable the check for a subject string you must pass
95 this option to pcre_exec() or pcre_dfa_exec().
96 If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, the
98 result is undefined and your program may crash.
99 Validity of UTF-16 strings
101 When you set the PCRE_UTF16 flag, the strings of 16-bit data units that
103 are passed as patterns and subjects are (by default) checked for valid‐
104 ity on entry to the relevant functions. Values other than those in the
105 surrogate range U+D800 to U+DFFF are independent code points. Values in
106 the surrogate range must be used in pairs in the correct manner.
107 If an invalid UTF-16 string is passed to PCRE, an error return is
109 given. At compile time, the only additional information is the offset
110 to the first data unit of the failing character. The run-time functions
111 pcre16_exec() and pcre16_dfa_exec() also pass back this information, as
112 well as a more detailed reason code if the caller has provided memory
113 in which to do this.
114 In some situations, you may already know that your strings are valid,
116 and therefore want to skip these checks in order to improve perfor‐
117 mance. If you set the PCRE_NO_UTF16_CHECK flag at compile time or at
118 run time, PCRE assumes that the pattern or subject it is given (respec‐
119 tively) contains only valid UTF-16 sequences. In this case, it does not
120 diagnose an invalid UTF-16 string. However, if an invalid string is
121 passed, the result is undefined.
122 Validity of UTF-32 strings
124 When you set the PCRE_UTF32 flag, the strings of 32-bit data units that
126 are passed as patterns and subjects are (by default) checked for valid‐
127 ity on entry to the relevant functions. This check allows only values
128 in the range U+0 to U+10FFFF, excluding the surrogate area U+D800 to
129 U+DFFF.
130 If an invalid UTF-32 string is passed to PCRE, an error return is
132 given. At compile time, the only additional information is the offset
133 to the first data unit of the failing character. The run-time functions
134 pcre32_exec() and pcre32_dfa_exec() also pass back this information, as
135 well as a more detailed reason code if the caller has provided memory
136 in which to do this.
137 In some situations, you may already know that your strings are valid,
139 and therefore want to skip these checks in order to improve perfor‐
140 mance. If you set the PCRE_NO_UTF32_CHECK flag at compile time or at
141 run time, PCRE assumes that the pattern or subject it is given (respec‐
142 tively) contains only valid UTF-32 sequences. In this case, it does not
143 diagnose an invalid UTF-32 string. However, if an invalid string is
144 passed, the result is undefined.
145 General comments about UTF modes
147 1. Codepoints less than 256 can be specified in patterns by either
149 braced or unbraced hexadecimal escape sequences (for example, \x{b3} or
150 \xb3). Larger values have to use braced sequences.
151 2. Octal numbers up to \777 are recognized, and in UTF-8 mode they
153 match two-byte characters for values greater than \177.
154 3. Repeat quantifiers apply to complete UTF characters, not to individ‐
156 ual data units, for example: \x{100}{3}.
157 4. The dot metacharacter matches one UTF character instead of a single
159 data unit.
160 5. The escape sequence \C can be used to match a single byte in UTF-8
162 mode, or a single 16-bit data unit in UTF-16 mode, or a single 32-bit
163 data unit in UTF-32 mode, but its use can lead to some strange effects
164 because it breaks up multi-unit characters (see the description of \C
165 in the pcrepattern documentation). The use of \C is not supported in
166 the alternative matching function pcre[16|32]_dfa_exec(), nor is it
167 supported in UTF mode by the JIT optimization of pcre[16|32]_exec(). If
168 JIT optimization is requested for a UTF pattern that contains \C, it
169 will not succeed, and so the matching will be carried out by the normal
170 interpretive function.
171 6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
173 test characters of any code value, but, by default, the characters that
174 PCRE recognizes as digits, spaces, or word characters remain the same
175 set as in non-UTF mode, all with values less than 256. This remains
176 true even when PCRE is built to include Unicode property support,
177 because to do otherwise would slow down PCRE in many common cases. Note
178 in particular that this applies to \b and \B, because they are defined
179 in terms of \w and \W. If you really want to test for a wider sense of,
180 say, "digit", you can use explicit Unicode property tests such as
181 \p{Nd}. Alternatively, if you set the PCRE_UCP option, the way that the
182 character escapes work is changed so that Unicode properties are used
183 to determine which characters match. There are more details in the sec‐
184 tion on generic character types in the pcrepattern documentation.
185 7. Similarly, characters that match the POSIX named character classes
187 are all low-valued characters, unless the PCRE_UCP option is set.
188 8. However, the horizontal and vertical white space matching escapes
190 (\h, \H, \v, and \V) do match all the appropriate Unicode characters,
191 whether or not PCRE_UCP is set.
192 9. Case-insensitive matching applies only to characters whose values
194 are less than 128, unless PCRE is built with Unicode property support.
195 A few Unicode characters such as Greek sigma have more than two code‐
196 points that are case-equivalent. Up to and including PCRE release 8.31,
197 only one-to-one case mappings were supported, but later releases (with
198 Unicode property support) do treat as case-equivalent all versions of
199 characters such as Greek sigma.
200
202 Philip Hazel
204 University Computing Service
205 Cambridge CB2 3QH, England.
206
208 Last updated: 27 February 2013
210 Copyright (c) 1997-2013 University of Cambridge.
211PCRE 8.33 27 February 2013 PCREUNICODE(3)