pcrecpp man page

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SYNOPSIS OF C++ WRAPPER

#include <pcrecpp.h>


DESCRIPTION

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


MATCHING INTERFACE

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
     NULL for the "i"th argument, or pass fewer arguments than
     number of sub-patterns, "i"th captured sub-pattern is
     ignored.
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.


PARTIAL MATCHES

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

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.


SCANNING TEXT INCREMENTALLY

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

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

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

The C++ wrapper was contributed by Google Inc.
Copyright © 2005 Google Inc.

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