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> 8Return to the <a href="index.html">PCRE index page</a>. 9</p> 10<p> 11This page is part of the PCRE HTML documentation. It was generated automatically 12from the original man page. If there is any nonsense in it, please consult the 13man page, in case the conversion went wrong. 14<br> 15<br><b> 16UTF-8, UTF-16, AND UNICODE PROPERTY SUPPORT 17</b><br> 18<P> 19From Release 8.30, in addition to its previous UTF-8 support, PCRE also 20supports UTF-16 by means of a separate 16-bit library. This can be built as 21well as, or instead of, the 8-bit library. 22</P> 23<br><b> 24UTF-8 SUPPORT 25</b><br> 26<P> 27In order process UTF-8 strings, you must build PCRE's 8-bit library with UTF 28support, and, in addition, you must call 29<a href="pcre_compile.html"><b>pcre_compile()</b></a> 30with 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 32strings that are matched against it are treated as UTF-8 strings instead of 33strings of 1-byte characters. 34</P> 35<br><b> 36UTF-16 SUPPORT 37</b><br> 38<P> 39In order process UTF-16 strings, you must build PCRE's 16-bit library with UTF 40support, and, in addition, you must call 41<a href="pcre_compile.html"><b>pcre16_compile()</b></a> 42with 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 44strings that are matched against it are treated as UTF-16 strings instead of 45strings of 16-bit characters. 46</P> 47<br><b> 48UTF SUPPORT OVERHEAD 49</b><br> 50<P> 51If you compile PCRE with UTF support, but do not use it at run time, the 52library will be a bit bigger, but the additional run time overhead is limited 53to testing the PCRE_UTF8/16 flag occasionally, so should not be very big. 54</P> 55<br><b> 56UNICODE PROPERTY SUPPORT 57</b><br> 58<P> 59If PCRE is built with Unicode character property support (which implies UTF 60support), the escape sequences \p{..}, \P{..}, and \X can be used. 61The available properties that can be tested are limited to the general 62category properties such as Lu for an upper case letter or Nd for a decimal 63number, the Unicode script names such as Arabic or Han, and the derived 64properties Any and L&. A full list is given in the 65<a href="pcrepattern.html"><b>pcrepattern</b></a> 66documentation. Only the short names for properties are supported. For example, 67\p{L} matches a letter. Its Perl synonym, \p{Letter}, is not supported. 68Furthermore, in Perl, many properties may optionally be prefixed by "Is", for 69compatibility with Perl 5.6. PCRE does not support this. 70<a name="utf8strings"></a></P> 71<br><b> 72Validity of UTF-8 strings 73</b><br> 74<P> 75When you set the PCRE_UTF8 flag, the byte strings passed as patterns and 76subjects are (by default) checked for validity on entry to the relevant 77functions. The entire string is checked before any other processing takes 78place. From release 7.3 of PCRE, the check is according the rules of RFC 3629, 79which are themselves derived from the Unicode specification. Earlier releases 80of PCRE followed the rules of RFC 2279, which allows the full range of 31-bit 81values (0 to 0x7FFFFFFF). The current check allows only values in the range U+0 82to U+10FFFF, excluding U+D800 to U+DFFF. 83</P> 84<P> 85The excluded code points are the "Surrogate Area" of Unicode. They are reserved 86for use by UTF-16, where they are used in pairs to encode codepoints with 87values greater than 0xFFFF. The code points that are encoded by UTF-16 pairs 88are available independently in the UTF-8 encoding. (In other words, the whole 89surrogate thing is a fudge for UTF-16 which unfortunately messes up UTF-8.) 90</P> 91<P> 92If an invalid UTF-8 string is passed to PCRE, an error return is given. At 93compile time, the only additional information is the offset to the first byte 94of 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 96detailed reason code if the caller has provided memory in which to do this. 97</P> 98<P> 99In some situations, you may already know that your strings are valid, and 100therefore want to skip these checks in order to improve performance, for 101example in the case of a long subject string that is being scanned repeatedly 102with different patterns. If you set the PCRE_NO_UTF8_CHECK flag at compile time 103or 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 105diagnose an invalid UTF-8 string. 106</P> 107<P> 108If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, what 109happens 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 111in the range 0 to 0x7FFFFFFF by <b>pcre_dfa_exec()</b> and the interpreted 112version of <b>pcre_exec()</b>. In other words, apart from the initial validity 113test, these functions (when in UTF-8 mode) handle strings according to the more 114liberal 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 116if the string does not even conform to RFC 2279, the result is undefined. Your 117program may crash. 118</P> 119<P> 120If you want to process strings of values in the full range 0 to 0x7FFFFFFF, 121encoded in a UTF-8-like manner as per the old RFC, you can set 122PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in this 123situation, you will have to apply your own validity check, and avoid the use of 124JIT optimization. 125<a name="utf16strings"></a></P> 126<br><b> 127Validity of UTF-16 strings 128</b><br> 129<P> 130When you set the PCRE_UTF16 flag, the strings of 16-bit data units that are 131passed as patterns and subjects are (by default) checked for validity on entry 132to the relevant functions. Values other than those in the surrogate range 133U+D800 to U+DFFF are independent code points. Values in the surrogate range 134must be used in pairs in the correct manner. 135</P> 136<P> 137If an invalid UTF-16 string is passed to PCRE, an error return is given. At 138compile time, the only additional information is the offset to the first data 139unit 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 141detailed reason code if the caller has provided memory in which to do this. 142</P> 143<P> 144In some situations, you may already know that your strings are valid, and 145therefore want to skip these checks in order to improve performance. If you set 146the PCRE_NO_UTF16_CHECK flag at compile time or at run time, PCRE assumes that 147the pattern or subject it is given (respectively) contains only valid UTF-16 148sequences. In this case, it does not diagnose an invalid UTF-16 string. 149</P> 150<br><b> 151General comments about UTF modes 152</b><br> 153<P> 1541. Codepoints less than 256 can be specified by either braced or unbraced 155hexadecimal escape sequences (for example, \x{b3} or \xb3). Larger values 156have to use braced sequences. 157</P> 158<P> 1592. Octal numbers up to \777 are recognized, and in UTF-8 mode, they match 160two-byte characters for values greater than \177. 161</P> 162<P> 1633. Repeat quantifiers apply to complete UTF characters, not to individual 164data units, for example: \x{100}{3}. 165</P> 166<P> 1674. The dot metacharacter matches one UTF character instead of a single data 168unit. 169</P> 170<P> 1715. The escape sequence \C can be used to match a single byte in UTF-8 mode, or 172a single 16-bit data unit in UTF-16 mode, but its use can lead to some strange 173effects because it breaks up multi-unit characters (see the description of \C 174in the 175<a href="pcrepattern.html"><b>pcrepattern</b></a> 176documentation). The use of \C is not supported in the alternative matching 177function <b>pcre[16]_dfa_exec()</b>, nor is it supported in UTF mode by the JIT 178optimization of <b>pcre[16]_exec()</b>. If JIT optimization is requested for a 179UTF pattern that contains \C, it will not succeed, and so the matching will 180be carried out by the normal interpretive function. 181</P> 182<P> 1836. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly 184test characters of any code value, but, by default, the characters that PCRE 185recognizes as digits, spaces, or word characters remain the same set as in 186non-UTF mode, all with values less than 256. This remains true even when PCRE 187is built to include Unicode property support, because to do otherwise would 188slow 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 190want to test for a wider sense of, say, "digit", you can use explicit Unicode 191property tests such as \p{Nd}. Alternatively, if you set the PCRE_UCP option, 192the way that the character escapes work is changed so that Unicode properties 193are used to determine which characters match. There are more details in the 194section on 195<a href="pcrepattern.html#genericchartypes">generic character types</a> 196in the 197<a href="pcrepattern.html"><b>pcrepattern</b></a> 198documentation. 199</P> 200<P> 2017. Similarly, characters that match the POSIX named character classes are all 202low-valued characters, unless the PCRE_UCP option is set. 203</P> 204<P> 2058. 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 207PCRE_UCP is set. 208</P> 209<P> 2109. Case-insensitive matching applies only to characters whose values are less 211than 128, unless PCRE is built with Unicode property support. Even when Unicode 212property support is available, PCRE still uses its own character tables when 213checking the case of low-valued characters, so as not to degrade performance. 214The Unicode property information is used only for characters with higher 215values. Furthermore, PCRE supports case-insensitive matching only when there is 216a one-to-one mapping between a letter's cases. There are a small number of 217many-to-one mappings in Unicode; these are not supported by PCRE. 218</P> 219<br><b> 220AUTHOR 221</b><br> 222<P> 223Philip Hazel 224<br> 225University Computing Service 226<br> 227Cambridge CB2 3QH, England. 228<br> 229</P> 230<br><b> 231REVISION 232</b><br> 233<P> 234Last updated: 14 April 2012 235<br> 236Copyright © 1997-2012 University of Cambridge. 237<br> 238<p> 239Return to the <a href="index.html">PCRE index page</a>. 240</p> 241