pcrecpp man page

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• 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

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

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 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);

   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)

  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.

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

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 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);

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);

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);

      --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 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 (*)

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()

  RE_Options & set_caseless(bool)

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

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

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);

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)) {
       ...;
     }

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 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));

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);

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);

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 © 2007 Google Inc.

Last updated: 08 January 2012

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