/[pcre]/code/trunk/doc/html/pcreapi.html

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-revision 548 by ph10,
Fri Jun 25 14:42:00 2010 UTC
+revision 567 by ph10,
Sat Nov  6 17:10:00 2010 UTC
 Line 1443 
 if that fails, by advancing the starting
  ordinary match again. There is some code that demonstrates how to do this in
  the
  <a href="pcredemo.html"><b>pcredemo</b></a>
- sample program.
+ sample program. In the most general case, you have to check to see if the
+ newline convention recognizes CRLF as a newline, and if so, and the current
+ character is CR followed by LF, advance the starting offset by two characters
+ instead of one.
  <pre>
    PCRE_NO_START_OPTIMIZE
  </pre>
-Line 1501 
 strings in the
+Line 1504 
 strings in the
  in the main
  <a href="pcre.html"><b>pcre</b></a>
  page. If an invalid UTF-8 sequence of bytes is found, <b>pcre_exec()</b> returns
- the error PCRE_ERROR_BADUTF8. If <i>startoffset</i> contains an invalid value,
+ the error PCRE_ERROR_BADUTF8. If <i>startoffset</i> contains a value that does
+ not point to the start of a UTF-8 character (or to the end of the subject),
  PCRE_ERROR_BADUTF8_OFFSET is returned.
  </P>
  <P>
-Line 1510 
 checks for performance reasons, you can
+Line 1514 
 checks for performance reasons, you can
  calling <b>pcre_exec()</b>. You might want to do this for the second and
  subsequent calls to <b>pcre_exec()</b> if you are making repeated calls to find
  all the matches in a single subject string. However, you should be sure that
- the value of <i>startoffset</i> points to the start of a UTF-8 character. When
+ the value of <i>startoffset</i> points to the start of a UTF-8 character (or the
- PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
+ end of the subject). When PCRE_NO_UTF8_CHECK is set, the effect of passing an
- subject, or a value of <i>startoffset</i> that does not point to the start of a
+ invalid UTF-8 string as a subject or an invalid value of <i>startoffset</i> is
- UTF-8 character, is undefined. Your program may crash.
+ undefined. Your program may crash.
  <pre>
    PCRE_PARTIAL_HARD
    PCRE_PARTIAL_SOFT
-Line 1522 
 These options turn on the partial matchi
+Line 1526 
 These options turn on the partial matchi
  compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match
  occurs if the end of the subject string is reached successfully, but there are
  not enough subject characters to complete the match. If this happens when
- PCRE_PARTIAL_HARD is set, <b>pcre_exec()</b> immediately returns
+ PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, matching continues by
- PCRE_ERROR_PARTIAL. Otherwise, if PCRE_PARTIAL_SOFT is set, matching continues
+ testing any remaining alternatives. Only if no complete match can be found is
- by testing any other alternatives. Only if they all fail is PCRE_ERROR_PARTIAL
+ PCRE_ERROR_PARTIAL returned instead of PCRE_ERROR_NOMATCH. In other words,
- returned (instead of PCRE_ERROR_NOMATCH). The portion of the string that
+ PCRE_PARTIAL_SOFT says that the caller is prepared to handle a partial match,
- was inspected when the partial match was found is set as the first matching
+ but only if no complete match can be found.
- string. There is a more detailed discussion in the
+ </P>
+ <P>
+ If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this case, if a
+ partial match is found, <b>pcre_exec()</b> immediately returns
+ PCRE_ERROR_PARTIAL, without considering any other alternatives. In other words,
+ when PCRE_PARTIAL_HARD is set, a partial match is considered to be more
+ important that an alternative complete match.
+ </P>
+ <P>
+ In both cases, the portion of the string that was inspected when the partial
+ match was found is set as the first matching string. There is a more detailed
+ discussion of partial and multi-segment matching, with examples, in the
  <a href="pcrepartial.html"><b>pcrepartial</b></a>
  documentation.
  </P>
-Line 1537 
 The string to be matched by pcre_exec
+Line 1552 
 The string to be matched by pcre_exec
  <P>
  The subject string is passed to <b>pcre_exec()</b> as a pointer in
  <i>subject</i>, a length (in bytes) in <i>length</i>, and a starting byte offset
- in <i>startoffset</i>. In UTF-8 mode, the byte offset must point to the start of
+ in <i>startoffset</i>. If this is negative or greater than the length of the
- a UTF-8 character. Unlike the pattern string, the subject may contain binary
+ subject, <b>pcre_exec()</b> returns PCRE_ERROR_BADOFFSET.
- zero bytes. When the starting offset is zero, the search for a match starts at
+ </P>
- the beginning of the subject, and this is by far the most common case.
+ <P>
+ In UTF-8 mode, the byte offset must point to the start of a UTF-8 character (or
+ the end of the subject). Unlike the pattern string, the subject may contain
+ binary zero bytes. When the starting offset is zero, the search for a match
+ starts at the beginning of the subject, and this is by far the most common
+ case.
  </P>
  <P>
  A non-zero starting offset is useful when searching for another match in the
-Line 1562 
 set to 4, it finds the second occurrence
+Line 1582 
 set to 4, it finds the second occurrence
  behind the starting point to discover that it is preceded by a letter.
  </P>
  <P>
+ Finding all the matches in a subject is tricky when the pattern can match an
+ empty string. It is possible to emulate Perl's /g behaviour by first trying the
+ match again at the same offset, with the PCRE_NOTEMPTY_ATSTART and
+ PCRE_ANCHORED options, and then if that fails, advancing the starting offset
+ and trying an ordinary match again. There is some code that demonstrates how to
+ do this in the
+ <a href="pcredemo.html"><b>pcredemo</b></a>
+ sample program. In the most general case, you have to check to see if the
+ newline convention recognizes CRLF as a newline, and if so, and the current
+ character is CR followed by LF, advance the starting offset by two characters
+ instead of one.
+ </P>
+ <P>
  If a non-zero starting offset is passed when the pattern is anchored, one
  attempt to match at the given offset is made. This can only succeed if the
  pattern does not require the match to be at the start of the subject.
-Line 1756 
 description above.
+Line 1789 
 description above.
    PCRE_ERROR_BADNEWLINE     (-23)
  </pre>
  An invalid combination of PCRE_NEWLINE_<i>xxx</i> options was given.
+ <pre>
+   PCRE_ERROR_BADOFFSET      (-24)
+ </pre>
+ The value of <i>startoffset</i> was negative or greater than the length of the
+ subject, that is, the value in <i>length</i>.
  </P>
  <P>
  Error numbers -16 to -20 and -22 are not used by <b>pcre_exec()</b>.
-Line 2050 
 is converted into PCRE_ERROR_PARTIAL if
+Line 2088 
 is converted into PCRE_ERROR_PARTIAL if
  there have been no complete matches, but there is still at least one matching
  possibility. The portion of the string that was inspected when the longest
  partial match was found is set as the first matching string in both cases.
+ There is a more detailed discussion of partial and multi-segment matching, with
+ examples, in the
+ <a href="pcrepartial.html"><b>pcrepartial</b></a>
+ documentation.
  <pre>
    PCRE_DFA_SHORTEST
  </pre>
-Line 2161 
 Cambridge CB2 3QH, England.
+Line 2203 
 Cambridge CB2 3QH, England.
  </P>
  <br><a name="SEC22" href="#TOC1">REVISION</a><br>
  <P>
- Last updated: 21 June 2010
+ Last updated: 06 November 2010
  <br>
  Copyright &copy; 1997-2010 University of Cambridge.
  <br>

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