/[pcre]/code/tags/pcre-6.7/doc/pcre.3

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-revision 43 by nigel,
Sat Feb 24 21:39:21 2007 UTC
+revision 49 by nigel,
Sat Feb 24 21:39:33 2007 UTC
 Line 44 
 pcre - Perl-compatible regular expressio
  .B int *\fIovector\fR, int \fIstringcount\fR, "const char ***\fIlistptr\fR);"
  .PP
  .br
+ .B void pcre_free_substring(const char *\fIstringptr\fR);
+ .PP
+ .br
+ .B void pcre_free_substring_list(const char **\fIstringptr\fR);
+ .PP
+ .br
  .B const unsigned char *pcre_maketables(void);
  .PP
  .br
-Line 70 
 pcre - Perl-compatible regular expressio
+Line 76 
 pcre - Perl-compatible regular expressio
  The PCRE library is a set of functions that implement regular expression
  pattern matching using the same syntax and semantics as Perl 5, with just a few
  differences (see below). The current implementation corresponds to Perl 5.005,
- with some additional features from the Perl development release.
+ with some additional features from later versions. This includes some
+ experimental, incomplete support for UTF-8 encoded strings. Details of exactly
+ what is and what is not supported are given below.
  PCRE has its own native API, which is described in this document. There is also
  a set of wrapper functions that correspond to the POSIX regular expression API.
-Line 84 
 contain the major and minor release numb
+Line 92 
 contain the major and minor release numb
  use these to include support for different releases.
  The functions \fBpcre_compile()\fR, \fBpcre_study()\fR, and \fBpcre_exec()\fR
- are used for compiling and matching regular expressions, while
+ are used for compiling and matching regular expressions.
- \fBpcre_copy_substring()\fR, \fBpcre_get_substring()\fR, and
+ The functions \fBpcre_copy_substring()\fR, \fBpcre_get_substring()\fR, and
  \fBpcre_get_substring_list()\fR are convenience functions for extracting
- captured substrings from a matched subject string. The function
+ captured substrings from a matched subject string; \fBpcre_free_substring()\fR
- \fBpcre_maketables()\fR is used (optionally) to build a set of character tables
+ and \fBpcre_free_substring_list()\fR are also provided, to free the memory used
- in the current locale for passing to \fBpcre_compile()\fR.
+ for extracted strings.
+ 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_fullinfo()\fR is used to find out information about a
  compiled pattern; \fBpcre_info()\fR is an obsolete version which returns only
-Line 223 
 This option inverts the "greediness" of
+Line 235 
 This option inverts the "greediness" of
  greedy by default, but become greedy if followed by "?". It is not compatible
  with Perl. It can also be set by a (?U) option setting within the pattern.
+   PCRE_UTF8
+ This option causes PCRE to regard both the pattern and the subject as strings
+ of UTF-8 characters instead of just byte strings. However, it is available only
+ if PCRE has been built to include UTF-8 support. If not, the use of this option
+ provokes an error. Support for UTF-8 is new, experimental, and incomplete.
+ Details of exactly what it entails are given below.
  .SH STUDYING A PATTERN
  When a pattern is going to be used several times, it is worth spending more
-Line 323 
 no back references.
+Line 343 
 no back references.
  Return information about the first character of any matched string, for a
  non-anchored pattern. 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
+ such as (cat|cow|coyote), it is returned in the integer pointed to by
  \fIwhere\fR. Otherwise, if either
  (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
-Line 332 
 starts with "^", or
+Line 352 
 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
+ -1 is returned, indicating that the pattern matches only at the start of a
- start of a subject string or after any "\\n" within the string. Otherwise -2 is
+ subject string or after any "\\n" within the string. Otherwise -2 is returned.
- returned. For anchored patterns, -2 is returned.
+ For anchored patterns, -2 is returned.
    PCRE_INFO_FIRSTTABLE
-Line 550 
 is a pointer to the vector of integer of
+Line 570 
 is a pointer to the vector of integer of
  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
+ ran out of space in \fIovector\fR, the value passed as \fIstringcount\fR should
- \fIstringcount\fR should be the size of the vector divided by three.
+ 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
+ \fIbuffersize\fR, while for \fBpcre_get_substring()\fR a new block of memory 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
-Line 590 
 string. This can be distinguished from a
+Line 610 
 string. This can be distinguished from a
  inspecting the appropriate offset in \fIovector\fR, which is negative for unset
  substrings.
+ The two convenience functions \fBpcre_free_substring()\fR and
+ \fBpcre_free_substring_list()\fR can be used to free the memory returned by
+ a previous call of \fBpcre_get_substring()\fR or
+ \fBpcre_get_substring_list()\fR, respectively. They do nothing more than call
+ the function pointed to by \fBpcre_free\fR, which of course could be called
+ directly from a C program. However, PCRE is used in some situations where it is
+ linked via a special interface to another programming language which cannot use
+ \fBpcre_free\fR directly; it is for these cases that the functions are
+ provided.
  .SH LIMITATIONS
-Line 650 
 patterns using the non-Perl item (?R).
+Line 679 
 patterns using the non-Perl item (?R).
  with the settings of captured strings when part of a pattern is repeated. For
  example, matching "aba" against the pattern /^(a(b)?)+$/ sets $2 to the value
  "b", but matching "aabbaa" against /^(aa(bb)?)+$/ leaves $2 unset. However, if
- the pattern is changed to /^(aa(b(b))?)+$/ then $2 (and $3) get set.
+ the pattern is changed to /^(aa(b(b))?)+$/ then $2 (and $3) are set.
  In Perl 5.004 $2 is set in both cases, and that is also true of PCRE. If in the
  future Perl changes to a consistent state that is different, PCRE may change to
-Line 691 
 The syntax and semantics of the regular
+Line 720 
 The syntax and semantics of the regular
  described below. Regular expressions are also described in the Perl
  documentation and in a number of other books, some of which have copious
  examples. Jeffrey Friedl's "Mastering Regular Expressions", published by
- O'Reilly (ISBN 1-56592-257), covers them in great detail. The description
+ O'Reilly (ISBN 1-56592-257), covers them in great detail.
- here is intended as reference documentation.
+ The description here is intended as reference documentation. The basic
+ operation of PCRE is on strings of bytes. However, there is the beginnings of
+ some support for UTF-8 character strings. To use this support you must
+ configure PCRE to include it, and then call \fBpcre_compile()\fR with the
+ PCRE_UTF8 option. How this affects the pattern matching is described in the
+ final section of this document.
  A regular expression is a pattern that is matched against a subject string from
  left to right. Most characters stand for themselves in a pattern, and match the
-Line 920 
 end of the subject in both modes, and if
+Line 955 
 end of the subject in both modes, and if
  .SH FULL STOP (PERIOD, DOT)
  Outside a character class, a dot in the pattern matches any one character in
  the subject, including a non-printing character, but not (by default) newline.
- If the PCRE_DOTALL option is set, then dots match newlines as well. The
+ If the PCRE_DOTALL option is set, dots match newlines as well. The handling of
- handling of dot is entirely independent of the handling of circumflex and
+ dot is entirely independent of the handling of circumflex and dollar, the only
- dollar, the only relationship being that they both involve newline characters.
+ relationship being that they both involve newline characters. Dot has no
- Dot has no special meaning in a character class.
+ special meaning in a character class.
  .SH SQUARE BRACKETS
-Line 1213 
 to the string
+Line 1248 
 to the string
  fails, because it matches the entire string due to the greediness of the .*
  item.
- However, if a quantifier is followed by a question mark, then it ceases to be
+ However, if a quantifier is followed by a question mark, it ceases to be
  greedy, and instead matches the minimum number of times possible, so the
  pattern
-Line 1229 
 own right. Because it has two uses, it c
+Line 1264 
 own right. Because it has two uses, it c
  which matches one digit by preference, but can match two if that is the only
  way the rest of the pattern matches.
- If the PCRE_UNGREEDY option is set (an option which is not available in Perl)
+ If the PCRE_UNGREEDY option is set (an option which is not available in Perl),
- then the quantifiers are not greedy by default, but individual ones can be made
+ the quantifiers are not greedy by default, but individual ones can be made
  greedy by following them with a question mark. In other words, it inverts the
  default behaviour.
-Line 1239 
 is greater than 1 or with a limited maxi
+Line 1274 
 is greater than 1 or with a limited maxi
  compiled pattern, in proportion to the size of the minimum or maximum.
  If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equivalent
- to Perl's /s) is set, thus allowing the . to match newlines, then the pattern
+ to Perl's /s) is set, thus allowing the . to match newlines, the pattern is
- is implicitly anchored, because whatever follows will be tried against every
+ 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
-Line 1284 
 itself. So the pattern
+Line 1319 
 itself. So the pattern
  matches "sense and sensibility" and "response and responsibility", but not
  "sense and responsibility". If caseful matching is in force at the time of the
- back reference, then the case of letters is relevant. For example,
+ back reference, the case of letters is relevant. For example,
    ((?i)rah)\\s+\\1
-Line 1292 
 matches "rah rah" and "RAH RAH", but not
+Line 1327 
 matches "rah rah" and "RAH RAH", but not
  capturing subpattern is matched caselessly.
  There may be more than one back reference to the same subpattern. If a
- subpattern has not actually been used in a particular match, then any back
+ subpattern has not actually been used in a particular match, any back
  references to it always fail. For example, the pattern
    (a|(bc))\\2
-Line 1300 
 references to it always fail. For exampl
+Line 1335 
 references to it always fail. For exampl
  always fails if it starts to match "a" rather than "bc". Because there may be
  up to 99 back references, all digits following the backslash are taken
  as part of a potential back reference number. If the pattern continues with a
- digit character, then some delimiter must be used to terminate the back
+ digit character, some delimiter must be used to terminate the back reference.
- reference. If the PCRE_EXTENDED option is set, this can be whitespace.
+ If the PCRE_EXTENDED option is set, this can be whitespace. Otherwise an empty
- Otherwise an empty comment can be used.
+ comment can be used.
  A back reference that occurs inside the parentheses to which it refers fails
  when the subpattern is first used, so, for example, (a\\1) never matches.
-Line 1311 
 example, the pattern
+Line 1346 
 example, the pattern
    (a|b\\1)+
- matches any number of "a"s and also "aba", "ababaa" etc. At each iteration of
+ matches any number of "a"s and also "aba", "ababbaa" etc. At each iteration of
  the subpattern, the back reference matches the character string corresponding
  to the previous iteration. In order for this to work, the pattern must be such
  that the first iteration does not need to match the back reference. This can be
-Line 1390 
 Several assertions (of any sort) may occ
+Line 1425 
 Several assertions (of any sort) may occ
  matches "foo" preceded by three digits that are not "999". Notice that each of
  the assertions is applied independently at the same point in the subject
  string. First there is a check that the previous three characters are all
- digits, then there is a check that the same three characters are not "999".
+ digits, and then there is a check that the same three characters are not "999".
  This pattern does \fInot\fR match "foo" preceded by six characters, the first
  of which are digits and the last three of which are not "999". For example, it
  doesn't match "123abcfoo". A pattern to do that is
-Line 1475 
 what follows matches the rest of the pat
+Line 1510 
 what follows matches the rest of the pat
    ^.*abcd$
- then the initial .* matches the entire string at first, but when this fails
+ the initial .* matches the entire string at first, but when this fails (because
- (because there is no following "a"), it backtracks to match all but the last
+ there is no following "a"), it backtracks to match all but the last character,
- character, then all but the last two characters, and so on. Once again the
+ then all but the last two characters, and so on. Once again the search for "a"
- search for "a" covers the entire string, from right to left, so we are no
+ covers the entire string, from right to left, so we are no better off. However,
- better off. However, if the pattern is written as
+ if the pattern is written as
    ^(?>.*)(?<=abcd)
- then there can be no backtracking for the .* item; it can match only the entire
+ 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
  characters. If it fails, the match fails immediately. For long strings, this
  approach makes a significant difference to the processing time.
-Line 1528 
 no-pattern (if present) is used. If ther
+Line 1563 
 no-pattern (if present) is used. If ther
  subpattern, a compile-time error occurs.
  There are two kinds of condition. If the text between the parentheses consists
- of a sequence of digits, then the condition is satisfied if the capturing
+ of a sequence of digits, the condition is satisfied if the capturing subpattern
- subpattern of that number has previously matched. Consider the following
+ of that number has previously matched. Consider the following pattern, which
- pattern, which contains non-significant white space to make it more readable
+ contains non-significant white space to make it more readable (assume the
- (assume the PCRE_EXTENDED option) and to divide it into three parts for ease
+ PCRE_EXTENDED option) and to divide it into three parts for ease of discussion:
- of discussion:
    ( \\( )?    [^()]+    (?(1) \\) )
-Line 1622 
 on at the top level. If additional paren
+Line 1656 
 on at the top level. If additional paren
    \\( ( ( (?>[^()]+) | (?R) )* ) \\)
       ^                        ^
       ^                        ^
- then the string they capture is "ab(cd)ef", the contents of the top level
+ the string they capture is "ab(cd)ef", the contents of the top level
  parentheses. If there are more than 15 capturing parentheses in a pattern, PCRE
  has to obtain extra memory to store data during a recursion, which it does by
  using \fBpcre_malloc\fR, freeing it via \fBpcre_free\fR afterwards. If no
-Line 1686 
 with the pattern above. The former gives
+Line 1720 
 with the pattern above. The former gives
  applied to a whole line of "a" characters, whereas the latter takes an
  appreciable time with strings longer than about 20 characters.
+ .SH UTF-8 SUPPORT
+ Starting at release 3.3, PCRE has some support for character strings encoded
+ in the UTF-8 format. This is incomplete, and is regarded as experimental. In
+ order to use it, you must configure PCRE to include UTF-8 support in the code,
+ and, in addition, you must call \fBpcre_compile()\fR with the PCRE_UTF8 option
+ flag. When you do this, both the pattern and any subject strings that are
+ matched against it are treated as UTF-8 strings instead of just strings of
+ bytes, but only in the cases that are mentioned below.
+ If you compile PCRE with UTF-8 support, but do not use it at run time, the
+ library will be a bit bigger, but the additional run time overhead is limited
+ to testing the PCRE_UTF8 flag in several places, so should not be very large.
+ PCRE assumes that the strings it is given contain valid UTF-8 codes. It does
+ not diagnose invalid UTF-8 strings. If you pass invalid UTF-8 strings to PCRE,
+ the results are undefined.
+ Running with PCRE_UTF8 set causes these changes in the way PCRE works:
+. In a pattern, the escape sequence \\x{...}, where the contents of the braces
+ is a string of hexadecimal digits, is interpreted as a UTF-8 character whose
+ code number is the given hexadecimal number, for example: \\x{1234}. This
+ inserts from one to six literal bytes into the pattern, using the UTF-8
+ encoding. If a non-hexadecimal digit appears between the braces, the item is
+ not recognized.
+. The original hexadecimal escape sequence, \\xhh, generates a two-byte UTF-8
+ character if its value is greater than 127.
+. Repeat quantifiers are NOT correctly handled if they follow a multibyte
+ character. For example, \\x{100}* and \\xc3+ do not work. If you want to
+ repeat such characters, you must enclose them in non-capturing parentheses,
+ for example (?:\\x{100}), at present.
+. The dot metacharacter matches one UTF-8 character instead of a single byte.
+. Unlike literal UTF-8 characters, the dot metacharacter followed by a
+ repeat quantifier does operate correctly on UTF-8 characters instead of
+ single bytes.
+. Although the \\x{...} escape is permitted in a character class, characters
+ whose values are greater than 255 cannot be included in a class.
+. A class is matched against a UTF-8 character instead of just a single byte,
+ but it can match only characters whose values are less than 256. Characters
+ with greater values always fail to match a class.
+. Repeated classes work correctly on multiple characters.
+. Classes containing just a single character whose value is greater than 127
+ (but less than 256), for example, [\\x80] or [^\\x{93}], do not work because
+ these are optimized into single byte matches. In the first case, of course,
+ the class brackets are just redundant.
+. Lookbehind assertions move backwards in the subject by a fixed number of
+ characters instead of a fixed number of bytes. Simple cases have been tested
+ to work correctly, but there may be hidden gotchas herein.
+. The character types such as \\d and \\w do not work correctly with UTF-8
+ characters. They continue to test a single byte.
+. Anything not explicitly mentioned here continues to work in bytes rather
+ than in characters.
+ The following UTF-8 features of Perl 5.6 are not implemented:
+. The escape sequence \\C to match a single byte.
+. The use of Unicode tables and properties and escapes \\p, \\P, and \\X.
  .SH AUTHOR
  Philip Hazel <ph10@cam.ac.uk>
  .br
-Line 1697 
 Cambridge CB2 3QG, England.
+Line 1802 
 Cambridge CB2 3QG, England.
  .br
  Phone: +44 1223 334714
- Last updated: 27 January 2000
+ Last updated: 28 August 2000,
+ .br
+   the 250th anniversary of the death of J.S. Bach.
  .br
  Copyright (c) 1997-2000 University of Cambridge.

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