271 lines
12 KiB
HTML
271 lines
12 KiB
HTML
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<html>
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<head>
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<title>pcreunicode specification</title>
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</head>
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<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
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<h1>pcreunicode man page</h1>
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<p>
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Return to the <a href="index.html">PCRE index page</a>.
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</p>
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<p>
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This page is part of the PCRE HTML documentation. It was generated automatically
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from the original man page. If there is any nonsense in it, please consult the
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man page, in case the conversion went wrong.
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<br>
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<br><b>
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UTF-8, UTF-16, UTF-32, AND UNICODE PROPERTY SUPPORT
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</b><br>
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<P>
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As well as UTF-8 support, PCRE also supports UTF-16 (from release 8.30) and
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UTF-32 (from release 8.32), by means of two additional libraries. They can be
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built as well as, or instead of, the 8-bit library.
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</P>
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<br><b>
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UTF-8 SUPPORT
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</b><br>
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<P>
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In order process UTF-8 strings, you must build PCRE's 8-bit library with UTF
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support, and, in addition, you must call
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<a href="pcre_compile.html"><b>pcre_compile()</b></a>
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with the PCRE_UTF8 option flag, or the pattern must start with the sequence
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(*UTF8) or (*UTF). When either of these is the case, both the pattern and any
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subject strings that are matched against it are treated as UTF-8 strings
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instead of strings of individual 1-byte characters.
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</P>
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<br><b>
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UTF-16 AND UTF-32 SUPPORT
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</b><br>
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<P>
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In order process UTF-16 or UTF-32 strings, you must build PCRE's 16-bit or
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32-bit library with UTF support, and, in addition, you must call
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<a href="pcre16_compile.html"><b>pcre16_compile()</b></a>
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or
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<a href="pcre32_compile.html"><b>pcre32_compile()</b></a>
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with the PCRE_UTF16 or PCRE_UTF32 option flag, as appropriate. Alternatively,
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the pattern must start with the sequence (*UTF16), (*UTF32), as appropriate, or
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(*UTF), which can be used with either library. When UTF mode is set, both the
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pattern and any subject strings that are matched against it are treated as
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UTF-16 or UTF-32 strings instead of strings of individual 16-bit or 32-bit
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characters.
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</P>
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<br><b>
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UTF SUPPORT OVERHEAD
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</b><br>
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<P>
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If you compile PCRE with UTF support, but do not use it at run time, the
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library will be a bit bigger, but the additional run time overhead is limited
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to testing the PCRE_UTF[8|16|32] flag occasionally, so should not be very big.
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</P>
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<br><b>
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UNICODE PROPERTY SUPPORT
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</b><br>
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<P>
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If PCRE is built with Unicode character property support (which implies UTF
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support), the escape sequences \p{..}, \P{..}, and \X can be used.
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The available properties that can be tested are limited to the general
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category properties such as Lu for an upper case letter or Nd for a decimal
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number, the Unicode script names such as Arabic or Han, and the derived
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properties Any and L&. Full lists is given in the
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<a href="pcrepattern.html"><b>pcrepattern</b></a>
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and
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<a href="pcresyntax.html"><b>pcresyntax</b></a>
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documentation. Only the short names for properties are supported. For example,
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\p{L} matches a letter. Its Perl synonym, \p{Letter}, is not supported.
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Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
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compatibility with Perl 5.6. PCRE does not support this.
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<a name="utf8strings"></a></P>
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<br><b>
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Validity of UTF-8 strings
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</b><br>
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<P>
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When you set the PCRE_UTF8 flag, the byte strings passed as patterns and
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subjects are (by default) checked for validity on entry to the relevant
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functions. The entire string is checked before any other processing takes
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place. From release 7.3 of PCRE, the check is according the rules of RFC 3629,
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which are themselves derived from the Unicode specification. Earlier releases
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of PCRE followed the rules of RFC 2279, which allows the full range of 31-bit
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values (0 to 0x7FFFFFFF). The current check allows only values in the range U+0
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to U+10FFFF, excluding the surrogate area and the non-characters.
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</P>
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<P>
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Characters in the "Surrogate Area" of Unicode are reserved for use by UTF-16,
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where they are used in pairs to encode codepoints with values greater than
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0xFFFF. The code points that are encoded by UTF-16 pairs are available
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independently in the UTF-8 and UTF-32 encodings. (In other words, the whole
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surrogate thing is a fudge for UTF-16 which unfortunately messes up UTF-8 and
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UTF-32.)
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</P>
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<P>
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Also excluded are the "Non-Character" code points, which are U+FDD0 to U+FDEF
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and the last two code points in each plane, U+??FFFE and U+??FFFF.
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</P>
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<P>
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If an invalid UTF-8 string is passed to PCRE, an error return is given. At
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compile time, the only additional information is the offset to the first byte
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of the failing character. The run-time functions <b>pcre_exec()</b> and
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<b>pcre_dfa_exec()</b> also pass back this information, as well as a more
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detailed reason code if the caller has provided memory in which to do this.
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</P>
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<P>
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In some situations, you may already know that your strings are valid, and
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therefore want to skip these checks in order to improve performance, for
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example in the case of a long subject string that is being scanned repeatedly.
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If you set the PCRE_NO_UTF8_CHECK flag at compile time or at run time, PCRE
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assumes that the pattern or subject it is given (respectively) contains only
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valid UTF-8 codes. In this case, it does not diagnose an invalid UTF-8 string.
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</P>
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<P>
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Note that passing PCRE_NO_UTF8_CHECK to <b>pcre_compile()</b> just disables the
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check for the pattern; it does not also apply to subject strings. If you want
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to disable the check for a subject string you must pass this option to
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<b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>.
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</P>
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<P>
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If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, the result
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is undefined and your program may crash.
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<a name="utf16strings"></a></P>
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<br><b>
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Validity of UTF-16 strings
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</b><br>
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<P>
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When you set the PCRE_UTF16 flag, the strings of 16-bit data units that are
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passed as patterns and subjects are (by default) checked for validity on entry
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to the relevant functions. Values other than those in the surrogate range
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U+D800 to U+DFFF are independent code points. Values in the surrogate range
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must be used in pairs in the correct manner.
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</P>
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<P>
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Excluded are the "Non-Character" code points, which are U+FDD0 to U+FDEF
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and the last two code points in each plane, U+??FFFE and U+??FFFF.
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</P>
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<P>
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If an invalid UTF-16 string is passed to PCRE, an error return is given. At
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compile time, the only additional information is the offset to the first data
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unit of the failing character. The run-time functions <b>pcre16_exec()</b> and
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<b>pcre16_dfa_exec()</b> also pass back this information, as well as a more
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detailed reason code if the caller has provided memory in which to do this.
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</P>
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<P>
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In some situations, you may already know that your strings are valid, and
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therefore want to skip these checks in order to improve performance. If you set
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the PCRE_NO_UTF16_CHECK flag at compile time or at run time, PCRE assumes that
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the pattern or subject it is given (respectively) contains only valid UTF-16
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sequences. In this case, it does not diagnose an invalid UTF-16 string.
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However, if an invalid string is passed, the result is undefined.
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<a name="utf32strings"></a></P>
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<br><b>
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Validity of UTF-32 strings
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</b><br>
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<P>
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When you set the PCRE_UTF32 flag, the strings of 32-bit data units that are
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passed as patterns and subjects are (by default) checked for validity on entry
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to the relevant functions. This check allows only values in the range U+0
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to U+10FFFF, excluding the surrogate area U+D800 to U+DFFF, and the
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"Non-Character" code points, which are U+FDD0 to U+FDEF and the last two
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characters in each plane, U+??FFFE and U+??FFFF.
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</P>
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<P>
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If an invalid UTF-32 string is passed to PCRE, an error return is given. At
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compile time, the only additional information is the offset to the first data
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unit of the failing character. The run-time functions <b>pcre32_exec()</b> and
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<b>pcre32_dfa_exec()</b> also pass back this information, as well as a more
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detailed reason code if the caller has provided memory in which to do this.
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</P>
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<P>
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In some situations, you may already know that your strings are valid, and
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therefore want to skip these checks in order to improve performance. If you set
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the PCRE_NO_UTF32_CHECK flag at compile time or at run time, PCRE assumes that
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the pattern or subject it is given (respectively) contains only valid UTF-32
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sequences. In this case, it does not diagnose an invalid UTF-32 string.
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However, if an invalid string is passed, the result is undefined.
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</P>
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<br><b>
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General comments about UTF modes
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</b><br>
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<P>
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1. Codepoints less than 256 can be specified in patterns by either braced or
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unbraced hexadecimal escape sequences (for example, \x{b3} or \xb3). Larger
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values have to use braced sequences.
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</P>
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<P>
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2. Octal numbers up to \777 are recognized, and in UTF-8 mode they match
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two-byte characters for values greater than \177.
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</P>
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<P>
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3. Repeat quantifiers apply to complete UTF characters, not to individual
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data units, for example: \x{100}{3}.
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</P>
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<P>
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4. The dot metacharacter matches one UTF character instead of a single data
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unit.
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</P>
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<P>
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5. The escape sequence \C can be used to match a single byte in UTF-8 mode, or
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a single 16-bit data unit in UTF-16 mode, or a single 32-bit data unit in
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UTF-32 mode, but its use can lead to some strange effects because it breaks up
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multi-unit characters (see the description of \C in the
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<a href="pcrepattern.html"><b>pcrepattern</b></a>
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documentation). The use of \C is not supported in the alternative matching
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function <b>pcre[16|32]_dfa_exec()</b>, nor is it supported in UTF mode by the
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JIT optimization of <b>pcre[16|32]_exec()</b>. If JIT optimization is requested
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for a UTF pattern that contains \C, it will not succeed, and so the matching
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will be carried out by the normal interpretive function.
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</P>
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<P>
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6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
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test characters of any code value, but, by default, the characters that PCRE
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recognizes as digits, spaces, or word characters remain the same set as in
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non-UTF mode, all with values less than 256. This remains true even when PCRE
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is built to include Unicode property support, because to do otherwise would
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slow down PCRE in many common cases. Note in particular that this applies to
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\b and \B, because they are defined in terms of \w and \W. If you really
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want to test for a wider sense of, say, "digit", you can use explicit Unicode
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property tests such as \p{Nd}. Alternatively, if you set the PCRE_UCP option,
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the way that the character escapes work is changed so that Unicode properties
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are used to determine which characters match. There are more details in the
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section on
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<a href="pcrepattern.html#genericchartypes">generic character types</a>
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in the
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<a href="pcrepattern.html"><b>pcrepattern</b></a>
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documentation.
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</P>
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<P>
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7. Similarly, characters that match the POSIX named character classes are all
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low-valued characters, unless the PCRE_UCP option is set.
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</P>
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<P>
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8. However, the horizontal and vertical white space matching escapes (\h, \H,
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\v, and \V) do match all the appropriate Unicode characters, whether or not
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PCRE_UCP is set.
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</P>
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<P>
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9. Case-insensitive matching applies only to characters whose values are less
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than 128, unless PCRE is built with Unicode property support. A few Unicode
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characters such as Greek sigma have more than two codepoints that are
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case-equivalent. Up to and including PCRE release 8.31, only one-to-one case
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mappings were supported, but later releases (with Unicode property support) do
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treat as case-equivalent all versions of characters such as Greek sigma.
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</P>
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<br><b>
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AUTHOR
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</b><br>
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<P>
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Philip Hazel
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<br>
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University Computing Service
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<br>
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Cambridge CB2 3QH, England.
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<br>
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</P>
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<br><b>
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REVISION
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</b><br>
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<P>
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Last updated: 11 November 2012
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<br>
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Copyright © 1997-2012 University of Cambridge.
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<br>
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<p>
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Return to the <a href="index.html">PCRE index page</a>.
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</p>
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