pcrecpp(3) — Linux manual page

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:https://www.pcre.org/⟩.  If you have a bug report for this
       manual page, see
       ⟨http:https://bugs.exim.org/enter_bug.cgi?product=PCRE⟩.  This page was
       obtained from the tarball pcre-8.45.tar.gz fetched from
       ⟨ftp:https://ftp.csx.cam.ac.uk/pub/software/programming/pcre/⟩ on
       2021-08-27.  If you discover any rendering problems in this HTML
       version 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 manual page), send a mail to
       [email protected]

PCRE 8.30                    08 January 2012                  PCRECPP(3)

Pages that refer to this page: pcreapi(3)