/[pcre]/code/tags/pcre-2.06/pcre.3

Diff of /code/tags/pcre-2.06/pcre.3

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-revision 27 by nigel,
Sat Feb 24 21:38:49 2007 UTC
+revision 35 by nigel,
Sat Feb 24 21:39:05 2007 UTC
 Line 13 
 pcre - Perl-compatible regular expressio
  .B const unsigned char *\fItableptr\fR);
  .PP
  .br
- .B const unsigned char *pcre_maketables(void);
- .PP
- .br
  .B pcre_extra *pcre_study(const pcre *\fIcode\fR, int \fIoptions\fR,
  .ti +5n
  .B const char **\fIerrptr\fR);
-Line 23 
 pcre - Perl-compatible regular expressio
+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 \fIoptions\fR, int *\fIovector\fR, int \fIovecsize\fR);
+ .PP
+ .br
+ .B int pcre_copy_substring(const char *\fIsubject\fR, int *\fIovector\fR,
+ .ti +5n
+ .B int \fIstringcount\fR, int \fIstringnumber\fR, char *\fIbuffer\fR,
+ .ti +5n
+ .B int \fIbuffersize\fR);
+ .PP
+ .br
+ .B int pcre_get_substring(const char *\fIsubject\fR, int *\fIovector\fR,
+ .ti +5n
+ .B int \fIstringcount\fR, int \fIstringnumber\fR,
+ .ti +5n
+ .B const char **\fIstringptr\fR);
+ .PP
+ .br
+ .B int pcre_get_substring_list(const char *\fIsubject\fR,
  .ti +5n
- .B int *\fIovector\fR, int \fIovecsize\fR);
+ .B int *\fIovector\fR, int \fIstringcount\fR, "const char ***\fIlistptr\fR);"
+ .PP
+ .br
+ .B const unsigned char *pcre_maketables(void);
  .PP
  .br
  .B int pcre_info(const pcre *\fIcode\fR, int *\fIoptptr\fR, int
-Line 51 
 PCRE has its own native API, which is de
+Line 70 
 PCRE has its own native API, which is de
  a set of wrapper functions that correspond to the POSIX API. See
  \fBpcreposix (3)\fR.
- The three functions \fBpcre_compile()\fR, \fBpcre_study()\fR, and
+ The functions \fBpcre_compile()\fR, \fBpcre_study()\fR, and \fBpcre_exec()\fR
- \fBpcre_exec()\fR are used for compiling and matching regular expressions. The
+ are used for compiling and matching regular expressions, while
- function \fBpcre_maketables()\fR is used (optionally) to build a set of
+ \fBpcre_copy_substring()\fR, \fBpcre_get_substring()\fR, and
- character tables in the current locale for passing to \fBpcre_compile()\fR.
+ \fBpcre_get_substring_list()\fR are convenience functions for extracting
+ captured substrings from a matched subject string. The function
+ \fBpcre_maketables()\fR is used (optionally) to build a set of character tables
+ in the current locale for passing to \fBpcre_compile()\fR.
  The function \fBpcre_info()\fR is used to find out information about a compiled
  pattern, while the function \fBpcre_version()\fR returns a pointer to a string
-Line 227 
 treated as letters), the following code
+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.
+ .SH INFORMATION ABOUT A PATTERN
+ The \fBpcre_info()\fR function returns information about a compiled pattern.
+ Its yield is the number of capturing subpatterns, or one of the following
+ negative numbers:
+   PCRE_ERROR_NULL       the argument \fIcode\fR was NULL
+   PCRE_ERROR_BADMAGIC   the "magic number" was not found
+ If the \fIoptptr\fR argument is not NULL, a copy of the options with which the
+ pattern was compiled is placed in the integer it points to. These option bits
+ are those specified in the call to \fBpcre_compile()\fR, modified by any
+ top-level option settings within the pattern itself, and with the PCRE_ANCHORED
+ bit set if the form of the pattern implies that it can match only at the start
+ of a subject string.
+ If the pattern is not anchored and the \fIfirstcharptr\fR argument is not NULL,
+ it is used to pass back information about the first character of any matched
+ string. If there is a fixed first character, e.g. from a pattern such as
+ (cat|cow|coyote), then it is returned in the integer pointed to by
+ \fIfirstcharptr\fR. Otherwise, if either
+   (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
+       starts with "^", or
+   (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
+       (if it were set, the pattern would be anchored),
+ then -1 is returned, indicating that the pattern matches only at the
+ start of a subject string or after any "\\n" within the string. Otherwise -2 is
+ returned.
  .SH MATCHING A PATTERN
  The function \fBpcre_exec()\fR is called to match a subject string against a
  pre-compiled pattern, which is passed in the \fIcode\fR argument. If the
  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 262 
 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 290 
 is the number of pairs that have been se
+Line 369 
 is the number of pairs that have been se
  subpatterns, the return value from a successful match is 1, indicating that
  just the first pair of offsets has been set.
+ Some convenience functions are provided for extracting the captured substrings
+ as separate strings. These are described in the following section.
  It is possible for an capturing subpattern number \fIn+1\fR to match some
  part of the subject when subpattern \fIn\fR has not been used at all. For
  example, if the string "abc" is matched against the pattern (a|(z))(bc)
-Line 350 
 call via \fBpcre_malloc()\fR fails, this
+Line 432 
 call via \fBpcre_malloc()\fR fails, this
  the end of matching.
- .SH INFORMATION ABOUT A PATTERN
+ .SH EXTRACTING CAPTURED SUBSTRINGS
- The \fBpcre_info()\fR function returns information about a compiled pattern.
+ Captured substrings can be accessed directly by using the offsets returned by
- Its yield is the number of capturing subpatterns, or one of the following
+ \fBpcre_exec()\fR in \fIovector\fR. For convenience, the functions
- negative numbers:
+ \fBpcre_copy_substring()\fR, \fBpcre_get_substring()\fR, and
+ \fBpcre_get_substring_list()\fR are provided for extracting captured substrings
+ as new, separate, zero-terminated strings. A substring that contains a binary
+ zero is correctly extracted and has a further zero added on the end, but the
+ result does not, of course, function as a C string.
+ The first three arguments are the same for all three functions: \fIsubject\fR
+ is the subject string which has just been successfully matched, \fIovector\fR
+ is a pointer to the vector of integer offsets that was passed to
+ \fBpcre_exec()\fR, and \fIstringcount\fR is the number of substrings that
+ were captured by the match, including the substring that matched the entire
+ regular expression. This is the value returned by \fBpcre_exec\fR if it
+ is greater than zero. If \fBpcre_exec()\fR returned zero, indicating that it
+ ran out of space in \fIovector\fR, then the value passed as
+ \fIstringcount\fR should be the size of the vector divided by three.
+ The functions \fBpcre_copy_substring()\fR and \fBpcre_get_substring()\fR
+ extract a single substring, whose number is given as \fIstringnumber\fR. A
+ value of zero extracts the substring that matched the entire pattern, while
+ higher values extract the captured substrings. For \fBpcre_copy_substring()\fR,
+ the string is placed in \fIbuffer\fR, whose length is given by
+ \fIbuffersize\fR, while for \fBpcre_get_substring()\fR a new block of store is
+ obtained via \fBpcre_malloc\fR, and its address is returned via
+ \fIstringptr\fR. The yield of the function is the length of the string, not
+ including the terminating zero, or one of
-   PCRE_ERROR_NULL       the argument \fIcode\fR was NULL
+   PCRE_ERROR_NOMEMORY       (-6)
-   PCRE_ERROR_BADMAGIC   the "magic number" was not found
- If the \fIoptptr\fR argument is not NULL, a copy of the options with which the
+ The buffer was too small for \fBpcre_copy_substring()\fR, or the attempt to get
- pattern was compiled is placed in the integer it points to.
+ memory failed for \fBpcre_get_substring()\fR.
+   PCRE_ERROR_NOSUBSTRING    (-7)
+ There is no substring whose number is \fIstringnumber\fR.
+ The \fBpcre_get_substring_list()\fR function extracts all available substrings
+ and builds a list of pointers to them. All this is done in a single block of
+ memory which is obtained via \fBpcre_malloc\fR. The address of the memory block
+ is returned via \fIlistptr\fR, which is also the start of the list of string
+ pointers. The end of the list is marked by a NULL pointer. The yield of the
+ function is zero if all went well, or
+   PCRE_ERROR_NOMEMORY       (-6)
+ if the attempt to get the memory block failed.
+ When any of these functions encounter a substring that is unset, which can
+ happen when capturing subpattern number \fIn+1\fR matches some part of the
+ subject, but subpattern \fIn\fR has not been used at all, they return an empty
+ string. This can be distinguished from a genuine zero-length substring by
+ inspecting the appropriate offset in \fIovector\fR, which is negative for unset
+ substrings.
- If the \fIfirstcharptr\fR argument is not NULL, is is used to pass back
- information about the first character of any matched string. If there is a
- fixed first character, e.g. from a pattern such as (cat|cow|coyote), then it is
- returned in the integer pointed to by \fIfirstcharptr\fR. Otherwise, if the
- pattern was compiled with the PCRE_MULTILINE option, and every branch started
- with "^", then -1 is returned, indicating that the pattern will match at the
- start of a subject string or after any "\\n" within the string. Otherwise -2 is
- returned.
  .SH LIMITATIONS
-Line 636 
 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 672 
 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 723 
 The minus (hyphen) character can be used
+Line 847 
 The minus (hyphen) character can be used
  character class. For example, [d-m] matches any letter between d and m,
  inclusive. If a minus character is required in a class, it must be escaped with
  a backslash or appear in a position where it cannot be interpreted as
- indicating a range, typically as the first or last character in the class. It
+ indicating a range, typically as the first or last character in the class.
- is not possible to have the character "]" as the end character of a range,
- since a sequence such as [w-] is interpreted as a class of two characters. The
+ It is not possible to have the literal character "]" as the end character of a
- octal or hexadecimal representation of "]" can, however, be used to end a
+ range. A pattern such as [W-]46] is interpreted as a class of two characters
- range.
+ ("W" and "-") followed by a literal string "46]", so it would match "W46]" or
+ "-46]". However, if the "]" is escaped with a backslash it is interpreted as
+ the end of range, so [W-\\]46] is interpreted as a single class containing a
+ range followed by two separate characters. The octal or hexadecimal
+ representation of "]" can also be used to end a range.
  Ranges operate in ASCII collating sequence. They can also be used for
  characters specified numerically, for example [\\000-\\037]. If a range that
-Line 963 
 When a parenthesized subpattern is quant
+Line 1091 
 When a parenthesized subpattern is quant
  is greater than 1 or with a limited maximum, more store is required for the
  compiled pattern, in proportion to the size of the minimum or maximum.
- If a pattern starts with .* then it is implicitly anchored, since whatever
+ If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equivalent
- follows will be tried against every character position in the subject string.
+ to Perl's /s) is set, thus allowing the . to match newlines, then the pattern
- PCRE treats this as though it were preceded by \\A.
+ is implicitly anchored, because whatever follows will be tried against every
+ character position in the subject string, so there is no point in retrying the
+ overall match at any position after the first. PCRE treats such a pattern as
+ though it were preceded by \\A. In cases where it is known that the subject
+ string contains no newlines, it is worth setting PCRE_DOTALL when the pattern
+ begins with .* in order to obtain this optimization, or alternatively using ^
+ to indicate anchoring explicitly.
  When a capturing subpattern is repeated, the value captured is the substring
  that matched the final iteration. For example, after
-Line 1115 
 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 1156 
 of characters that an identical standalo
+Line 1290 
 of characters that an identical standalo
  the current point in the subject string.
  Once-only subpatterns are not capturing subpatterns. Simple cases such as the
- above example can be though of as a maximizing repeat that must swallow
+ above example can be thought of as a maximizing repeat that must swallow
  everything it can. So, while both \\d+ and \\d+? are prepared to adjust the
  number of digits they match in order to make the rest of the pattern match,
  (?>\\d+) can only match an entire sequence of digits.
-Line 1175 
 proceeds from left to right, PCRE will l
+Line 1309 
 proceeds from left to right, PCRE will l
  then see if what follows matches the rest of the pattern. If the pattern is
  specified as
-   .*abcd$
+   ^.*abcd$
  then the initial .* matches the entire string at first, but when this fails, it
  backtracks to match all but the last character, then all but the last two
-Line 1183 
 characters, and so on. Once again the se
+Line 1317 
 characters, and so on. Once again the se
  from right to left, so we are no better off. However, if the pattern is written
  as
-   (?>.*)(?<=abcd)
+   ^(?>.*)(?<=abcd)
  then there can be no backtracking for the .* item; it can match only the entire
  string. The subsequent lookbehind assertion does a single test on the last four
-Line 1257 
 required behaviour is usually the most e
+Line 1391 
 required behaviour is usually the most e
  contains a lot of discussion about optimizing regular expressions for efficient
  performance.
+ When a pattern begins with .* and the PCRE_DOTALL option is set, the pattern is
+ implicitly anchored by PCRE, since it can match only at the start of a subject
+ string. However, if PCRE_DOTALL is not set, PCRE cannot make this optimization,
+ because the . metacharacter does not then match a newline, and if the subject
+ string contains newlines, the pattern may match from the character immediately
+ following one of them instead of from the very start. For example, the pattern
+    (.*) second
+ matches the subject "first\\nand second" (where \\n stands for a newline
+ character) with the first captured substring being "and". In order to do this,
+ PCRE has to retry the match starting after every newline in the subject.
+ If you are using such a pattern with subject strings that do not contain
+ newlines, the best performance is obtained by setting PCRE_DOTALL, or starting
+ the pattern with ^.* to indicate explicit anchoring. That saves PCRE from
+ having to scan along the subject looking for a newline to restart at.
  .SH AUTHOR
  Philip Hazel <ph10@cam.ac.uk>
-Line 1269 
 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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