/[pcre]/code/trunk/pcre.3

Diff of /code/trunk/pcre.3

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-revision 34 by nigel,
Sat Feb 24 21:39:01 2007 UTC
+revision 35 by nigel,
Sat Feb 24 21:39:05 2007 UTC
 Line 20 
 pcre - Perl-compatible regular expressio
  .br
  .B int pcre_exec(const pcre *\fIcode\fR, "const pcre_extra *\fIextra\fR,"
  .ti +5n
- .B "const char *\fIsubject\fR," int \fIlength\fR, int \fIoptions\fR,
+ .B "const char *\fIsubject\fR," int \fIlength\fR, int \fIstartoffset\fR,
  .ti +5n
- .B int *\fIovector\fR, int \fIovecsize\fR);
+ .B int \fIoptions\fR, int *\fIovector\fR, int \fIovecsize\fR);
  .PP
  .br
  .B int pcre_copy_substring(const char *\fIsubject\fR, int *\fIovector\fR,
 Line 249 
 treated as letters), the following code
  The tables are built in memory that is obtained via \fBpcre_malloc\fR. The
  pointer that is passed to \fBpcre_compile\fR is saved with the compiled
  pattern, and the same tables are used via this pointer by \fBpcre_study()\fR
- and \fBpcre_match()\fR. Thus for any single pattern, compilation, studying and
+ and \fBpcre_exec()\fR. Thus for any single pattern, compilation, studying and
  matching all happen in the same locale, but different patterns can be compiled
  in different locales. It is the caller's responsibility to ensure that the
  memory containing the tables remains available for as long as it is needed.
 Line 293 
 pre-compiled pattern, which is passed in
  pattern has been studied, the result of the study should be passed in the
  \fIextra\fR argument. Otherwise this must be NULL.
- The subject string is passed as a pointer in \fIsubject\fR and a length in
- \fIlength\fR. Unlike the pattern string, it may contain binary zero characters.
  The PCRE_ANCHORED option can be passed in the \fIoptions\fR argument, whose
  unused bits must be zero. However, if a pattern was compiled with
  PCRE_ANCHORED, or turned out to be anchored by virtue of its contents, it
-Line 316 
 should not match it nor (except in multi
+Line 313 
 should not match it nor (except in multi
  it. Setting this without PCRE_MULTILINE (at compile time) causes dollar never
  to match.
+ The subject string is passed as a pointer in \fIsubject\fR, a length in
+ \fIlength\fR, and a starting offset in \fIstartoffset\fR. Unlike the pattern
+ string, it may contain binary zero characters. 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.
+ A non-zero starting offset is useful when searching for another match in the
+ same subject by calling \fBpcre_exec()\fR again after a previous success.
+ Setting \fIstartoffset\fR differs from just passing over a shortened string and
+ setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
+ lookbehind. For example, consider the pattern
+   \\Biss\\B
+ which finds occurrences of "iss" in the middle of words. (\\B matches only if
+ the current position in the subject is not a word boundary.) When applied to
+ the string "Mississipi" the first call to \fBpcre_exec()\fR finds the first
+ occurrence. If \fBpcre_exec()\fR is called again with just the remainder of the
+ subject, namely "issipi", it does not match, because \\B is always false at the
+ start of the subject, which is deemed to be a word boundary. However, if
+ \fBpcre_exec()\fR is passed the entire string again, but with \fIstartoffset\fR
+ set to 4, it finds the second occurrence of "iss" because it is able to look
+ behind the starting point to discover that it is preceded by a letter.
+ If a non-zero starting offset is passed when the pattern is anchored, one
+ attempt to match at the given offset is tried. This can only succeed if the
+ pattern does not require the match to be at the start of the subject.
  In general, a pattern matches a certain portion of the subject, and in
  addition, further substrings from the subject may be picked out by parts of the
  pattern. Following the usage in Jeffrey Friedl's book, this is called
-Line 730 
 first or last character matches \\w, res
+Line 755 
 first or last character matches \\w, res
  The \\A, \\Z, and \\z assertions differ from the traditional circumflex and
  dollar (described below) in that they only ever match at the very start and end
  of the subject string, whatever options are set. They are not affected by the
- PCRE_NOTBOL or PCRE_NOTEOL options. The difference between \\Z and \\z is that
+ PCRE_NOTBOL or PCRE_NOTEOL options. If the \fIstartoffset\fR argument of
- \\Z matches before a newline that is the last character of the string as well
+ \fBpcre_exec()\fR is non-zero, \\A can never match. The difference between \\Z
- as at the end of the string, whereas \\z matches only at the end.
+ and \\z is that \\Z matches before a newline that is the last character of the
+ string as well as at the end of the string, whereas \\z matches only at the
+ end.
  .SH CIRCUMFLEX AND DOLLAR
  Outside a character class, in the default matching mode, the circumflex
  character is an assertion which is true only if the current matching point is
- at the start of the subject string. Inside a character class, circumflex has an
+ at the start of the subject string. If the \fIstartoffset\fR argument of
- entirely different meaning (see below).
+ \fBpcre_exec()\fR is non-zero, circumflex can never match. Inside a character
+ class, circumflex has an entirely different meaning (see below).
  Circumflex need not be the first character of the pattern if a number of
  alternatives are involved, but it should be the first thing in each alternative
-Line 766 
 after and immediately before an internal
+Line 794 
 after and immediately before an internal
  addition to matching at the start and end of the subject string. For example,
  the pattern /^abc$/ matches the subject string "def\\nabc" in multiline mode,
  but not otherwise. Consequently, patterns that are anchored in single line mode
- because all branches start with "^" are not anchored in multiline mode. The
+ because all branches start with "^" are not anchored in multiline mode, and a
- PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
+ match for circumflex is possible when the \fIstartoffset\fR argument of
+ \fBpcre_exec()\fR is non-zero. The PCRE_DOLLAR_ENDONLY option is ignored if
+ PCRE_MULTILINE is set.
  Note that the sequences \\A, \\Z, and \\z can be used to match the start and
  end of the subject in both modes, and if all branches of a pattern start with
-Line 1219 
 matches an occurrence of "baz" that is p
+Line 1249 
 matches an occurrence of "baz" that is p
  preceded by "foo".
  Assertion subpatterns are not capturing subpatterns, and may not be repeated,
- because it makes no sense to assert the same thing several times. If an
+ because it makes no sense to assert the same thing several times. If any kind
- assertion contains capturing subpatterns within it, these are always counted
+ of assertion contains capturing subpatterns within it, these are counted for
- for the purposes of numbering the capturing subpatterns in the whole pattern.
+ the purposes of numbering the capturing subpatterns in the whole pattern.
- Substring capturing is carried out for positive assertions, but it does not
+ However, substring capturing is carried out only for positive assertions,
- make sense for negative assertions.
+ because it does not make sense for negative assertions.
  Assertions count towards the maximum of 200 parenthesized subpatterns.
-Line 1390 
 Cambridge CB2 3QG, England.
+Line 1420 
 Cambridge CB2 3QG, England.
  .br
  Phone: +44 1223 334714
+ Last updated: 10 June 1999
+ .br
  Copyright (c) 1997-1999 University of Cambridge.

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