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X11R7.4 - man page for pcrecpp (x11r4 section 3)

PCRECPP(3)			     Library Functions Manual			       PCRECPP(3)

       PCRE - Perl-compatible regular expressions.


       #include <pcrecpp.h>


       The  C++  wrapper  for  PCRE was provided by Google Inc. Some additional functionality was
       added by Giuseppe Maxia. This brief man	page  was  constructed	from  the  notes  in  the
       pcrecpp.h file, which should be consulted for further details.


       The "FullMatch" operation checks that supplied text matches a supplied pattern exactly. If
       pointer arguments are supplied, it copies matched sub-strings that match sub-patterns into

	 Example: successful match
	    pcrecpp::RE re("h.*o");

	 Example: unsuccessful match (requires full match):
	    pcrecpp::RE re("e");

	 Example: creating a temporary RE object:

       You can pass in a "const char*" or a "string" for "text". The examples below tend to use a
       const char*. You can, as in the different examples above, store the RE  object  explicitly
       in  a  variable or use a temporary RE object. The examples below use one mode or the other
       arbitrarily. Either could correctly be used for any of these examples.

       You must supply extra pointer arguments to extract matched subpieces.

	 Example: extracts "ruby" into "s" and 1234 into "i"
	    int i;
	    string s;
	    pcrecpp::RE re("(\\w+):(\\d+)");
	    re.FullMatch("ruby:1234", &s, &i);

	 Example: does not try to extract any extra sub-patterns
	    re.FullMatch("ruby:1234", &s);

	 Example: does not try to extract into NULL
	    re.FullMatch("ruby:1234", NULL, &i);

	 Example: integer overflow causes failure
	    !re.FullMatch("ruby:1234567891234", NULL, &i);

	 Example: fails because there aren't enough sub-patterns:
	    !pcrecpp::RE("\\w+:\\d+").FullMatch("ruby:1234", &s);

	 Example: fails because string cannot be stored in integer
	    !pcrecpp::RE("(.*)").FullMatch("ruby", &i);

       The provided pointer arguments can be pointers to any scalar numeric type, or one of:

	  string	(matched piece is copied to string)
	  StringPiece	(StringPiece is mutated to point to matched piece)
	  T		(where "bool T::ParseFrom(const char*, int)" exists)
	  NULL		(the corresponding matched sub-pattern is not copied)

       The function returns true iff all of the following conditions are satisfied:

	 a. "text" matches "pattern" exactly;

	 b. The number of matched sub-patterns is >= number of supplied

	 c. The "i"th argument has a suitable type for holding the
	    string captured as the "i"th sub-pattern. If you pass in
	    void * NULL for the "i"th argument, or a non-void * NULL
	    of the correct type, or pass fewer arguments than the
	    number of sub-patterns, "i"th captured sub-pattern is

       CAVEAT: An optional sub-pattern that does not exist in the matched string is assigned  the
       empty  string. Therefore, the following will return false (because the empty string is not
       a valid number):

	  int number;
	  pcrecpp::RE::FullMatch("abc", "[a-z]+(\\d+)?", &number);

       The matching interface supports at most 16 arguments per call.  If you need more, consider
       using the more general interface pcrecpp::RE::DoMatch. See pcrecpp.h for the signature for

       NOTE: Do not use no_arg, which is used internally to mark the end of a  list  of  optional
       arguments, as a placeholder for missing arguments, as this can lead to segfaults.


       You  can  use the "QuoteMeta" operation to insert backslashes before all potentially mean-
       ingful characters in a string. The returned string, used as  a  regular	expression,  will
       exactly match the original string.

	    string quoted = RE::QuoteMeta(unquoted);

       Note  that it's legal to escape a character even if it has no special meaning in a regular
       expression -- so this function does that. (This also makes it identical to the perl  func-
       tion  of  the  same  name;  see	"perldoc -f quotemeta".)  For example, "1.5-2.0?" becomes


       You can use the "PartialMatch" operation when you want the pattern to match any	substring
       of the text.

	 Example: simple search for a string:

	 Example: find first number in a string:
	    int number;
	    pcrecpp::RE re("(\\d+)");
	    re.PartialMatch("x*100 + 20", &number);
	    assert(number == 100);


       By default, pattern and text are plain text, one byte per character. The UTF8 flag, passed
       to the constructor, causes both pattern and string to be treated as UTF-8  text,  still	a
       byte  stream  but potentially multiple bytes per character. In practice, the text is like-
       lier to be UTF-8 than the pattern, but the match returned may depend on the UTF8 flag,  so
       always  use  it when matching UTF8 text. For example, "." will match one byte normally but
       with UTF8 set may match up to three bytes of a multi-byte character.

	    pcrecpp::RE_Options options;
	    pcrecpp::RE re(utf8_pattern, options);

	 Example: using the convenience function UTF8():
	    pcrecpp::RE re(utf8_pattern, pcrecpp::UTF8());

       NOTE: The UTF8 flag is ignored if pcre was not configured with the
	     --enable-utf8 flag.


       PCRE defines some modifiers to change the behavior of the regular expression  engine.  The
       C++ wrapper defines an auxiliary class, RE_Options, as a vehicle to pass such modifiers to
       a RE class. Currently, the following modifiers are supported:

	  modifier		description		  Perl corresponding

	  PCRE_CASELESS 	case insensitive match	    /i
	  PCRE_MULTILINE	multiple lines match	    /m
	  PCRE_DOTALL		dot matches newlines	    /s
	  PCRE_DOLLAR_ENDONLY	$ matches only at end	    N/A
	  PCRE_EXTRA		strict escape parsing	    N/A
	  PCRE_EXTENDED 	ignore whitespaces	    /x
	  PCRE_UTF8		handles UTF8 chars	    built-in
	  PCRE_UNGREEDY 	reverses * and *?	    N/A
	  PCRE_NO_AUTO_CAPTURE	disables capturing parens   N/A (*)

       (*) Both Perl and PCRE allow non capturing parentheses  by  means  of  the  "?:"  modifier
       within the pattern itself. e.g. (?:ab|cd) does not capture, while (ab|cd) does.

       For a full account on how each modifier works, please check the PCRE API reference page.

       For  each  modifier, there are two member functions whose name is made out of the modifier
       in lowercase, without the "PCRE_" prefix. For instance, PCRE_CASELESS is handled by

	 bool caseless()

       which returns true if the modifier is set, and

	 RE_Options & set_caseless(bool)

       which sets or unsets  the  modifier.  Moreover,	PCRE_EXTRA_MATCH_LIMIT	can  be  accessed
       through the set_match_limit() and match_limit() member functions. Setting match_limit to a
       non-zero value will limit the execution of pcre to keep it  from  doing	bad  things  like
       blowing the stack or taking an eternity to return a result. A value of 5000 is good enough
       to stop stack blowup in a 2MB thread stack. Setting match_limit	to  zero  disables  match
       limiting.    Alternatively,    you    can    call   match_limit_recursion()   which   uses
       PCRE_EXTRA_MATCH_LIMIT_RECURSION to limit how much PCRE recurses. match_limit() limits the
       number  of  matches PCRE does; match_limit_recursion() limits the depth of internal recur-
       sion, and therefore the amount of stack that is used.

       Normally, to pass one or more modifiers to a RE class, you declare  a  RE_Options  object,
       set the appropriate options, and pass this object to a RE constructor. Example:

	  RE_options opt;
	  if (RE("HELLO", opt).PartialMatch("hello world")) ...

       RE_options  has two constructors. The default constructor takes no arguments and creates a
       set of flags that are off by default. The optional parameter option_flags is to facilitate
       transfer of legacy code from C programs.  This lets you do


       However, new code is better off doing


       If  you are going to pass one of the most used modifiers, there are some convenience func-
       tions that return a RE_Options class with the  appropriate  modifier  already  set:  CASE-
       LESS(), UTF8(), MULTILINE(), DOTALL(), and EXTENDED().

       If  you need to set several options at once, and you don't want to go through the pains of
       declaring a RE_Options object and setting several options, there is a parallel method that
       give  you  such	ability  on the fly. You can concatenate several set_xxxxx() member func-
       tions, since each of them returns a reference to its class object. For  example,  to  pass
       PCRE_CASELESS,  PCRE_EXTENDED,  and  PCRE_MULTILINE  to	a  RE with one statement, you may

	  RE(" ^ xyz \\s+ .* blah$",


       The "Consume" operation may be useful if you want to repeatedly match regular  expressions
       at  the	front  of  a  string  and  skip over them as they match. This requires use of the
       "StringPiece" type, which represents a sub-range of a real string. Like RE, StringPiece is
       defined in the pcrecpp namespace.

	 Example: read lines of the form "var = value" from a string.
	    string contents = ...;		   // Fill string somehow
	    pcrecpp::StringPiece input(contents);  // Wrap in a StringPiece

	    string var;
	    int value;
	    pcrecpp::RE re("(\\w+) = (\\d+)\n");
	    while (re.Consume(&input, &var, &value)) {

       Each  successful  call  to  "Consume" will set "var/value", and also advance "input" so it
       points past the matched text.

       The "FindAndConsume" operation is similar to "Consume" but does not anchor your	match  at
       the  beginning  of  the	string. For example, you could extract all words from a string by
       repeatedly calling

	 pcrecpp::RE("(\\w+)").FindAndConsume(&input, &word)


       By default, if you pass a pointer to a numeric value, the  corresponding  text  is  inter-
       preted  as  a  base-10  number. You can instead wrap the pointer with a call to one of the
       operators Hex(), Octal(), or CRadix() to interpret the text in another  base.  The  CRadix
       operator  interprets  C-style  "0"  (base-8)  and "0x" (base-16) prefixes, but defaults to

	   int a, b, c, d;
	   pcrecpp::RE re("(.*) (.*) (.*) (.*)");
	   re.FullMatch("100 40 0100 0x40",
			pcrecpp::Octal(&a), pcrecpp::Hex(&b),
			pcrecpp::CRadix(&c), pcrecpp::CRadix(&d));

       will leave 64 in a, b, c, and d.


       You can replace the first match of "pattern" in "str" with "rewrite".   Within  "rewrite",
       backslash-escaped  digits  (\1  to  \9)	can be used to insert text matching corresponding
       parenthesized group from the pattern. \0 in "rewrite" refers to the entire matching  text.
       For example:

	 string s = "yabba dabba doo";
	 pcrecpp::RE("b+").Replace("d", &s);

       will  leave "s" containing "yada dabba doo". The result is true if the pattern matches and
       a replacement occurs, false otherwise.

       GlobalReplace is like Replace except that it replaces all occurrences of  the  pattern  in
       the string with the rewrite. Replacements are not subject to re-matching. For example:

	 string s = "yabba dabba doo";
	 pcrecpp::RE("b+").GlobalReplace("d", &s);

       will leave "s" containing "yada dada doo". It returns the number of replacements made.

       Extract	is  like  Replace,  except  that if the pattern matches, "rewrite" is copied into
       "out" (an additional argument) with substitutions.  The non-matching  portions  of  "text"
       are  ignored.  Returns true iff a match occurred and the extraction happened successfully;
       if no match occurs, the string is left unaffected.


       The C++ wrapper was contributed by Google Inc.
       Copyright (c) 2007 Google Inc.


       Last updated: 17 March 2009


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