.TH PCRECPP 3

.SH NAME

PCRE - Perl-compatible regular expressions.

.SH "SYNOPSIS OF C++ WRAPPER"

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.B #include <pcrecpp.h>

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.SH DESCRIPTION

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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 \fIpcrecpp.h\fP file, which should be consulted for

further details.

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.SH "MATCHING INTERFACE"

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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 them.

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  Example: successful match

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

     re.FullMatch("hello");

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  Example: unsuccessful match (requires full match):

     pcrecpp::RE re("e");

     !re.FullMatch("hello");

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  Example: creating a temporary RE object:

     pcrecpp::RE("h.*o").FullMatch("hello");

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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.

.P

You must supply extra pointer arguments to extract matched subpieces.

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  Example: extracts "ruby" into "s" and 1234 into "i"

     int i;

     string s;

     pcrecpp::RE re("(\e\ew+):(\e\ed+)");

     re.FullMatch("ruby:1234", &s, &i);

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  Example: does not try to extract any extra sub-patterns

     re.FullMatch("ruby:1234", &s);

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  Example: does not try to extract into NULL

     re.FullMatch("ruby:1234", NULL, &i);

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  Example: integer overflow causes failure

     !re.FullMatch("ruby:1234567891234", NULL, &i);

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  Example: fails because there aren't enough sub-patterns:

     !pcrecpp::RE("\e\ew+:\e\ed+").FullMatch("ruby:1234", &s);

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  Example: fails because string cannot be stored in integer

     !pcrecpp::RE("(.*)").FullMatch("ruby", &i);

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The provided pointer arguments can be pointers to any scalar numeric

type, or one of:

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   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)

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

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  a. "text" matches "pattern" exactly;

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

     pointers;

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  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

     ignored.

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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):

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   int number;

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

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The matching interface supports at most 16 arguments per call.

If you need more, consider using the more general interface

\fBpcrecpp::RE::DoMatch\fP. See \fBpcrecpp.h\fP for the signature for

\fBDoMatch\fP.

.P

NOTE: Do not use \fBno_arg\fP, 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.

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.SH "QUOTING METACHARACTERS"

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You can use the "QuoteMeta" operation to insert backslashes before all

potentially meaningful characters in a string. The returned string, used as a

regular expression, will exactly match the original string.

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  Example:

     string quoted = RE::QuoteMeta(unquoted);

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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 function of the same name; see "perldoc -f quotemeta".)

For example, "1.5-2.0?" becomes "1\e.5\e-2\e.0\e?".

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.SH "PARTIAL MATCHES"

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You can use the "PartialMatch" operation when you want the pattern

to match any substring of the text.

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  Example: simple search for a string:

     pcrecpp::RE("ell").PartialMatch("hello");

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  Example: find first number in a string:

     int number;

     pcrecpp::RE re("(\e\ed+)");

     re.PartialMatch("x*100 + 20", &number);

     assert(number == 100);

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.SH "UTF-8 AND THE MATCHING INTERFACE"

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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 likelier 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.

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  Example:

     pcrecpp::RE_Options options;

     options.set_utf8();

     pcrecpp::RE re(utf8_pattern, options);

     re.FullMatch(utf8_string);

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  Example: using the convenience function UTF8():

     pcrecpp::RE re(utf8_pattern, pcrecpp::UTF8());

     re.FullMatch(utf8_string);

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NOTE: The UTF8 flag is ignored if pcre was not configured with the

      --enable-utf8 flag.

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.SH "PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE"

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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:

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   modifier              description               Perl corresponding

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   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 (*)

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(*) 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.

.P

For a full account on how each modifier works, please check the

PCRE API reference page.

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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

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  bool caseless()

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which returns true if the modifier is set, and

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  RE_Options & set_caseless(bool)

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which sets or unsets the modifier. Moreover, PCRE_EXTRA_MATCH_LIMIT can be

accessed through the \fBset_match_limit()\fR and \fBmatch_limit()\fR member

functions. Setting \fImatch_limit\fR 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 \fImatch_limit\fR to zero disables

match limiting. Alternatively, you can call \fBmatch_limit_recursion()\fP

which uses PCRE_EXTRA_MATCH_LIMIT_RECURSION to limit how much PCRE

recurses. \fBmatch_limit()\fP limits the number of matches PCRE does;

\fBmatch_limit_recursion()\fP limits the depth of internal recursion, and

therefore the amount of stack that is used.

.P

Normally, to pass one or more modifiers to a RE class, you declare

a \fIRE_Options\fR object, set the appropriate options, and pass this

object to a RE constructor. Example:

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   RE_options opt;

   opt.set_caseless(true);

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

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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

\fIoption_flags\fR is to facilitate transfer of legacy code from C programs.

This lets you do

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   RE(pattern,

     RE_Options(PCRE_CASELESS|PCRE_MULTILINE)).PartialMatch(str);

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However, new code is better off doing

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   RE(pattern,

     RE_Options().set_caseless(true).set_multiline(true))

       .PartialMatch(str);

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If you are going to pass one of the most used modifiers, there are some

convenience functions that return a RE_Options class with the

appropriate modifier already set: \fBCASELESS()\fR, \fBUTF8()\fR,

\fBMULTILINE()\fR, \fBDOTALL\fR(), and \fBEXTENDED()\fR.

.P

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 \fBset_xxxxx()\fR member functions, 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 write:

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

     RE_Options()

       .set_caseless(true)

       .set_extended(true)

       .set_multiline(true)).PartialMatch(sometext);

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.SH "SCANNING TEXT INCREMENTALLY"

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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.

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  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("(\e\ew+) = (\e\ed+)\en");

     while (re.Consume(&input, &var, &value)) {

       ...;

     }

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Each successful call to "Consume" will set "var/value", and also

advance "input" so it points past the matched text.

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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

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

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.SH "PARSING HEX/OCTAL/C-RADIX NUMBERS"

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By default, if you pass a pointer to a numeric value, the

corresponding text is interpreted 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 base-10.

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  Example:

    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));

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

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.SH "REPLACING PARTS OF STRINGS"

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You can replace the first match of "pattern" in "str" with "rewrite".

Within "rewrite", backslash-escaped digits (\e1 to \e9) can be

used to insert text matching corresponding parenthesized group

from the pattern. \e0 in "rewrite" refers to the entire matching

text. For example:

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  string s = "yabba dabba doo";

  pcrecpp::RE("b+").Replace("d", &s);

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will leave "s" containing "yada dabba doo". The result is true if the pattern

matches and a replacement occurs, false otherwise.

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\fBGlobalReplace\fP is like \fBReplace\fP except that it replaces all

occurrences of the pattern in the string with the rewrite. Replacements are

not subject to re-matching. For example:

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  string s = "yabba dabba doo";

  pcrecpp::RE("b+").GlobalReplace("d", &s);

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

replacements made.

.P

\fBExtract\fP is like \fBReplace\fP, 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.

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.SH AUTHOR

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The C++ wrapper was contributed by Google Inc.

Copyright (c) 2007 Google Inc.

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.SH REVISION

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Last updated: 17 March 2009

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