pcre_compile()
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. . .
</a>
pcre16_compile()
with the PCRE_UTF16 option flag, or the pattern must start with the sequence (*UTF16). When either of these is the case, both the pattern and any subject strings that are matched against it are treated as UTF-16 strings instead of strings of 16-bit characters. . .
pcrepattern
documentation. Only the short names for properties are supported. For example, \ep{L} matches a letter. Its Perl synonym, \ep{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. . . HTML <a name="utf8strings"></a>
The excluded code points are the "Surrogate Area" of Unicode. They are reserved for use by UTF-16, where they are used in pairs to encode codepoints with values greater than 0xFFFF. The code points that are encoded by UTF-16 pairs are available independently in the UTF-8 encoding. (In other words, the whole surrogate thing is a fudge for UTF-16 which unfortunately messes up UTF-8.)
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 run-time functions pcre_exec() and pcre_dfa_exec() also pass back this information, as well as a more detailed reason code if the caller has provided memory in which to do this.
In some situations, you may already know that your strings are valid, and therefore want to skip these checks in order to improve performance, for example in the case of a long subject string that is being scanned repeatedly with different patterns. 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.
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 pcre_dfa_exec() and the interpreted version of pcre_exec(). 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 pcre_exec() 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.
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.
.
.
HTML <a name="utf16strings"></a>
If an invalid UTF-16 string is passed to PCRE, an error return is given. At compile time, the only additional information is the offset to the first data unit of the failing character. The run-time functions pcre16_exec() and pcre16_dfa_exec() also pass back this information, as well as a more detailed reason code if the caller has provided memory in which to do this.
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_UTF16_CHECK flag at compile time or at run time, PCRE assumes that the pattern or subject it is given (respectively) contains only valid UTF-16 sequences. In this case, it does not diagnose an invalid UTF-16 string. . .
2. Octal numbers up to \e777 are recognized, and in UTF-8 mode, they match two-byte characters for values greater than \e177.
3. Repeat quantifiers apply to complete UTF characters, not to individual data units, for example: \ex{100}{3}.
4. The dot metacharacter matches one UTF character instead of a single data unit.
5. The escape sequence \eC can be used to match a single byte in UTF-8 mode, or
a single 16-bit data unit in UTF-16 mode, but its use can lead to some strange
effects because it breaks up multi-unit characters (see the description of \eC
in the
HREF
pcrepattern
documentation). The use of \eC is not supported in the alternative matching
function pcre[16]_dfa_exec(), nor is it supported in UTF mode by the JIT
optimization of pcre[16]_exec(). If JIT optimization is requested for a
UTF pattern that contains \eC, it will not succeed, and so the matching will
be carried out by the normal interpretive function.
6. The character escapes \eb, \eB, \ed, \eD, \es, \eS, \ew, and \eW 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 in
non-UTF mode, 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
\eb and \eB, because they are defined in terms of \ew and \eW. If you really
want to test for a wider sense of, say, "digit", you can use explicit Unicode
property tests such as \ep{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
HTML <a href="pcrepattern.html#genericchartypes">
</a>
generic character types
in the
HREF
pcrepattern
documentation.
7. Similarly, characters that match the POSIX named character classes are all low-valued characters, unless the PCRE_UCP option is set.
8. However, the horizontal and vertical white space matching escapes (\eh, \eH, \ev, and \eV) do match all the appropriate Unicode characters, whether or not PCRE_UCP is set.
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. . .
Philip Hazel University Computing Service Cambridge CB2 3QH, England.. .
Last updated: 14 April 2012 Copyright (c) 1997-2012 University of Cambridge.