| <html> |
| <head> |
| <title>pcreunicode specification</title> |
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| <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"> |
| <h1>pcreunicode man page</h1> |
| <p> |
| Return to the <a href="index.html">PCRE index page</a>. |
| </p> |
| <p> |
| This page is part of the PCRE HTML documentation. It was generated automatically |
| from the original man page. If there is any nonsense in it, please consult the |
| man page, in case the conversion went wrong. |
| <br> |
| <br><b> |
| UTF-8 AND UNICODE PROPERTY SUPPORT |
| </b><br> |
| <P> |
| In order process UTF-8 strings, you must build PCRE to include UTF-8 support in |
| the code, and, in addition, you must call |
| <a href="pcre_compile.html"><b>pcre_compile()</b></a> |
| with the PCRE_UTF8 option flag, or the pattern must start with the sequence |
| (*UTF8). When either of these is the case, both the pattern and any subject |
| strings that are matched against it are treated as UTF-8 strings instead of |
| strings of 1-byte characters. PCRE does not support any other formats (in |
| particular, it does not support UTF-16). |
| </P> |
| <P> |
| If you compile PCRE with UTF-8 support, but do not use it at run time, the |
| library will be a bit bigger, but the additional run time overhead is limited |
| to testing the PCRE_UTF8 flag occasionally, so should not be very big. |
| </P> |
| <P> |
| If PCRE is built with Unicode character property support (which implies UTF-8 |
| support), the escape sequences \p{..}, \P{..}, and \X are supported. |
| The available properties that can be tested are limited to the general |
| category properties such as Lu for an upper case letter or Nd for a decimal |
| number, the Unicode script names such as Arabic or Han, and the derived |
| properties Any and L&. A full list is given in the |
| <a href="pcrepattern.html"><b>pcrepattern</b></a> |
| documentation. Only the short names for properties are supported. For example, |
| \p{L} matches a letter. Its Perl synonym, \p{Letter}, is not supported. |
| Furthermore, in Perl, many properties may optionally be prefixed by "Is", for |
| compatibility with Perl 5.6. PCRE does not support this. |
| <a name="utf8strings"></a></P> |
| <br><b> |
| Validity of UTF-8 strings |
| </b><br> |
| <P> |
| When you set the PCRE_UTF8 flag, the strings passed as patterns and subjects |
| are (by default) checked for validity on entry to the relevant functions. From |
| release 7.3 of PCRE, the check is according the rules of RFC 3629, which are |
| themselves derived from the Unicode specification. Earlier releases of PCRE |
| followed the rules of RFC 2279, which allows the full range of 31-bit values (0 |
| to 0x7FFFFFFF). The current check allows only values in the range U+0 to |
| U+10FFFF, excluding U+D800 to U+DFFF. |
| </P> |
| <P> |
| The excluded code points are the "Low Surrogate Area" of Unicode, of which the |
| Unicode Standard says this: "The Low Surrogate Area does not contain any |
| character assignments, consequently no character code charts or namelists are |
| provided for this area. Surrogates are reserved for use with UTF-16 and then |
| must be used in pairs." The code points that are encoded by UTF-16 pairs are |
| available as independent code points in the UTF-8 encoding. (In other words, |
| the whole surrogate thing is a fudge for UTF-16 which unfortunately messes up |
| UTF-8.) |
| </P> |
| <P> |
| If an invalid UTF-8 string is passed to PCRE, an error return is given. At |
| compile time, the only additional information is the offset to the first byte |
| of the failing character. The runtime functions <b>pcre_exec()</b> and |
| <b>pcre_dfa_exec()</b> also pass back this information, as well as a more |
| detailed reason code if the caller has provided memory in which to do this. |
| </P> |
| <P> |
| In some situations, you may already know that your strings are valid, and |
| therefore want to skip these checks in order to improve performance. If you set |
| the PCRE_NO_UTF8_CHECK flag at compile time or at run time, PCRE assumes that |
| the pattern or subject it is given (respectively) contains only valid UTF-8 |
| codes. In this case, it does not diagnose an invalid UTF-8 string. |
| </P> |
| <P> |
| If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, what |
| happens depends on why the string is invalid. If the string conforms to the |
| "old" definition of UTF-8 (RFC 2279), it is processed as a string of characters |
| in the range 0 to 0x7FFFFFFF by <b>pcre_dfa_exec()</b> and the interpreted |
| version of <b>pcre_exec()</b>. In other words, apart from the initial validity |
| test, these functions (when in UTF-8 mode) handle strings according to the more |
| liberal rules of RFC 2279. However, the just-in-time (JIT) optimization for |
| <b>pcre_exec()</b> supports only RFC 3629. If you are using JIT optimization, or |
| if the string does not even conform to RFC 2279, the result is undefined. Your |
| program may crash. |
| </P> |
| <P> |
| If you want to process strings of values in the full range 0 to 0x7FFFFFFF, |
| encoded in a UTF-8-like manner as per the old RFC, you can set |
| PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in this |
| situation, you will have to apply your own validity check, and avoid the use of |
| JIT optimization. |
| </P> |
| <br><b> |
| General comments about UTF-8 mode |
| </b><br> |
| <P> |
| 1. An unbraced hexadecimal escape sequence (such as \xb3) matches a two-byte |
| UTF-8 character if the value is greater than 127. |
| </P> |
| <P> |
| 2. Octal numbers up to \777 are recognized, and match two-byte UTF-8 |
| characters for values greater than \177. |
| </P> |
| <P> |
| 3. Repeat quantifiers apply to complete UTF-8 characters, not to individual |
| bytes, for example: \x{100}{3}. |
| </P> |
| <P> |
| 4. The dot metacharacter matches one UTF-8 character instead of a single byte. |
| </P> |
| <P> |
| 5. The escape sequence \C can be used to match a single byte in UTF-8 mode, |
| but its use can lead to some strange effects because it breaks up multibyte |
| characters (see the description of \C in the |
| <a href="pcrepattern.html"><b>pcrepattern</b></a> |
| documentation). The use of \C is not supported in the alternative matching |
| function <b>pcre_dfa_exec()</b>, nor is it supported in UTF-8 mode by the JIT |
| optimization of <b>pcre_exec()</b>. If JIT optimization is requested for a UTF-8 |
| pattern that contains \C, it will not succeed, and so the matching will be |
| carried out by the normal interpretive function. |
| </P> |
| <P> |
| 6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly |
| test characters of any code value, but, by default, the characters that PCRE |
| recognizes as digits, spaces, or word characters remain the same set as before, |
| all with values less than 256. This remains true even when PCRE is built to |
| include Unicode property support, because to do otherwise would slow down PCRE |
| in many common cases. Note in particular that this applies to \b and \B, |
| because they are defined in terms of \w and \W. If you really want to test |
| for a wider sense of, say, "digit", you can use explicit Unicode property tests |
| such as \p{Nd}. Alternatively, if you set the PCRE_UCP option, the way that |
| the character escapes work is changed so that Unicode properties are used to |
| determine which characters match. There are more details in the section on |
| <a href="pcrepattern.html#genericchartypes">generic character types</a> |
| in the |
| <a href="pcrepattern.html"><b>pcrepattern</b></a> |
| documentation. |
| </P> |
| <P> |
| 7. Similarly, characters that match the POSIX named character classes are all |
| low-valued characters, unless the PCRE_UCP option is set. |
| </P> |
| <P> |
| 8. However, the horizontal and vertical whitespace matching escapes (\h, \H, |
| \v, and \V) do match all the appropriate Unicode characters, whether or not |
| PCRE_UCP is set. |
| </P> |
| <P> |
| 9. Case-insensitive matching applies only to characters whose values are less |
| than 128, unless PCRE is built with Unicode property support. Even when Unicode |
| property support is available, PCRE still uses its own character tables when |
| checking the case of low-valued characters, so as not to degrade performance. |
| The Unicode property information is used only for characters with higher |
| values. Furthermore, PCRE supports case-insensitive matching only when there is |
| a one-to-one mapping between a letter's cases. There are a small number of |
| many-to-one mappings in Unicode; these are not supported by PCRE. |
| </P> |
| <br><b> |
| AUTHOR |
| </b><br> |
| <P> |
| Philip Hazel |
| <br> |
| University Computing Service |
| <br> |
| Cambridge CB2 3QH, England. |
| <br> |
| </P> |
| <br><b> |
| REVISION |
| </b><br> |
| <P> |
| Last updated: 19 October 2011 |
| <br> |
| Copyright © 1997-2011 University of Cambridge. |
| <br> |
| <p> |
| Return to the <a href="index.html">PCRE index page</a>. |
| </p> |