NAME | SYNOPSIS OF C++ WRAPPER | DESCRIPTION | MATCHING INTERFACE | QUOTING METACHARACTERS | PARTIAL MATCHES | UTF-8 AND THE MATCHING INTERFACE | PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE | SCANNING TEXT INCREMENTALLY | PARSING HEX/OCTAL/C-RADIX NUMBERS | REPLACING PARTS OF STRINGS | AUTHOR | REVISION | COLOPHON

PCRECPP(3)                Library Functions Manual                PCRECPP(3)

NAME         top

       PCRE - Perl-compatible regular expressions.

SYNOPSIS OF C++ WRAPPER         top


       #include <pcrecpp.h>

DESCRIPTION         top


       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. Note that the C++ wrapper supports
       only the original 8-bit PCRE library. There is no 16-bit or 32-bit
       support at present.

MATCHING INTERFACE         top


       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.

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

         Example: unsuccessful match (requires full match):
            pcrecpp::RE re("e");
            !re.FullMatch("hello");

         Example: creating a temporary RE object:
            pcrecpp::RE("h.*o").FullMatch("hello");

       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
            pointers;

         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.

       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 DoMatch.

       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.

QUOTING METACHARACTERS         top


       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.

         Example:
            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 function of the same name; see
       "perldoc -f quotemeta".)  For example, "1.5-2.0?" becomes
       "1\.5\-2\.0\?".

PARTIAL MATCHES         top


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

         Example: simple search for a string:
            pcrecpp::RE("ell").PartialMatch("hello");

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

UTF-8 AND THE MATCHING INTERFACE         top


       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.

         Example:
            pcrecpp::RE_Options options;
            options.set_utf8();
            pcrecpp::RE re(utf8_pattern, options);
            re.FullMatch(utf8_string);

         Example: using the convenience function UTF8():
            pcrecpp::RE re(utf8_pattern, pcrecpp::UTF8());
            re.FullMatch(utf8_string);

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

PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE         top


       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 white spaces         /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 recursion, 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;
          opt.set_caseless(true);
          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

          RE(pattern,
            RE_Options(PCRE_CASELESS|PCRE_MULTILINE)).PartialMatch(str);

       However, new code is better off doing

          RE(pattern,
            RE_Options().set_caseless(true).set_multiline(true))
              .PartialMatch(str);

       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: CASELESS(), 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
       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:

          RE(" ^ xyz \\s+ .* blah$",
            RE_Options()
              .set_caseless(true)
              .set_extended(true)
              .set_multiline(true)).PartialMatch(sometext);

SCANNING TEXT INCREMENTALLY         top


       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)

PARSING HEX/OCTAL/C-RADIX NUMBERS         top


       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.

         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));

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

REPLACING PARTS OF STRINGS         top


       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.

AUTHOR         top


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

REVISION         top


       Last updated: 08 January 2012

COLOPHON         top

       This page is part of the PCRE (Perl Compatible Regular Expressions)
       project.  Information about the project can be found at 
       ⟨http://www.pcre.org/⟩.  If you have a bug report for this manual
       page, see ⟨http://bugs.exim.org/enter_bug.cgi?product=PCRE⟩.  This
       page was obtained from the tarball pcre-8.40.tar.gz fetched from 
       ⟨ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/⟩ on
       2017-05-03.  If you discover any rendering problems in this HTML ver‐
       sion of the page, or you believe there is a better or more up-to-date
       source for the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original man‐
       ual page), send a mail to man-pages@man7.org

PCRE 8.30                      08 January 2012                    PCRECPP(3)

Pages that refer to this page: pcreapi(3)