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revision 76 by nigel, Sat Feb 24 21:40:37 2007 UTC revision 77 by nigel, Sat Feb 24 21:40:45 2007 UTC
# Line 55  in the main Line 55  in the main
55  page.  page.
56  </P>  </P>
57  <P>  <P>
58    The remainder of this document discusses the patterns that are supported by
59    PCRE when its main matching function, <b>pcre_exec()</b>, is used.
60    From release 6.0, PCRE offers a second matching function,
61    <b>pcre_dfa_exec()</b>, which matches using a different algorithm that is not
62    Perl-compatible. The advantages and disadvantages of the alternative function,
63    and how it differs from the normal function, are discussed in the
64    <a href="pcrematching.html"><b>pcrematching</b></a>
65    page.
66    </P>
67    <P>
68  A regular expression is a pattern that is matched against a subject string from  A regular expression is a pattern that is matched against a subject string from
69  left to right. Most characters stand for themselves in a pattern, and match the  left to right. Most characters stand for themselves in a pattern, and match the
70  corresponding characters in the subject. As a trivial example, the pattern  corresponding characters in the subject. As a trivial example, the pattern
71  <pre>  <pre>
72    The quick brown fox    The quick brown fox
73  </pre>  </pre>
74  matches a portion of a subject string that is identical to itself. The power of  matches a portion of a subject string that is identical to itself. When
75  regular expressions comes from the ability to include alternatives and  caseless matching is specified (the PCRE_CASELESS option), letters are matched
76  repetitions in the pattern. These are encoded in the pattern by the use of  independently of case. In UTF-8 mode, PCRE always understands the concept of
77    case for characters whose values are less than 128, so caseless matching is
78    always possible. For characters with higher values, the concept of case is
79    supported if PCRE is compiled with Unicode property support, but not otherwise.
80    If you want to use caseless matching for characters 128 and above, you must
81    ensure that PCRE is compiled with Unicode property support as well as with
82    UTF-8 support.
83    </P>
84    <P>
85    The power of regular expressions comes from the ability to include alternatives
86    and repetitions in the pattern. These are encoded in the pattern by the use of
87  <i>metacharacters</i>, which do not stand for themselves but instead are  <i>metacharacters</i>, which do not stand for themselves but instead are
88  interpreted in some special way.  interpreted in some special way.
89  </P>  </P>
# Line 536  class as a literal string of bytes, or b Line 556  class as a literal string of bytes, or b
556  When caseless matching is set, any letters in a class represent both their  When caseless matching is set, any letters in a class represent both their
557  upper case and lower case versions, so for example, a caseless [aeiou] matches  upper case and lower case versions, so for example, a caseless [aeiou] matches
558  "A" as well as "a", and a caseless [^aeiou] does not match "A", whereas a  "A" as well as "a", and a caseless [^aeiou] does not match "A", whereas a
559  caseful version would. When running in UTF-8 mode, PCRE supports the concept of  caseful version would. In UTF-8 mode, PCRE always understands the concept of
560  case for characters with values greater than 128 only when it is compiled with  case for characters whose values are less than 128, so caseless matching is
561  Unicode property support.  always possible. For characters with higher values, the concept of case is
562    supported if PCRE is compiled with Unicode property support, but not otherwise.
563    If you want to use caseless matching for characters 128 and above, you must
564    ensure that PCRE is compiled with Unicode property support as well as with
565    UTF-8 support.
566  </P>  </P>
567  <P>  <P>
568  The newline character is never treated in any special way in character classes,  The newline character is never treated in any special way in character classes,
# Line 1462  description of the interface to the call Line 1486  description of the interface to the call
1486  documentation.  documentation.
1487  </P>  </P>
1488  <P>  <P>
1489  Last updated: 09 September 2004  Last updated: 28 February 2005
1490  <br>  <br>
1491  Copyright &copy; 1997-2004 University of Cambridge.  Copyright &copy; 1997-2005 University of Cambridge.
1492  <p>  <p>
1493  Return to the <a href="index.html">PCRE index page</a>.  Return to the <a href="index.html">PCRE index page</a>.
1494  </p>  </p>

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