349 lines
12 KiB
Groff
349 lines
12 KiB
Groff
.TH PCRECPP 3 "08 January 2012" "PCRE 8.30"
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.SH NAME
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PCRE - Perl-compatible regular expressions.
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.SH "SYNOPSIS OF C++ WRAPPER"
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.rs
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.sp
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.B #include <pcrecpp.h>
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.
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.SH DESCRIPTION
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.rs
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.sp
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The C++ wrapper for PCRE was provided by Google Inc. Some additional
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functionality was added by Giuseppe Maxia. This brief man page was constructed
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from the notes in the \fIpcrecpp.h\fP file, which should be consulted for
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further details. Note that the C++ wrapper supports only the original 8-bit
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PCRE library. There is no 16-bit or 32-bit support at present.
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.
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.
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.SH "MATCHING INTERFACE"
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.rs
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.sp
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The "FullMatch" operation checks that supplied text matches a supplied pattern
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exactly. If pointer arguments are supplied, it copies matched sub-strings that
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match sub-patterns into them.
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.sp
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Example: successful match
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pcrecpp::RE re("h.*o");
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re.FullMatch("hello");
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.sp
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Example: unsuccessful match (requires full match):
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pcrecpp::RE re("e");
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!re.FullMatch("hello");
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.sp
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Example: creating a temporary RE object:
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pcrecpp::RE("h.*o").FullMatch("hello");
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.sp
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You can pass in a "const char*" or a "string" for "text". The examples below
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tend to use a const char*. You can, as in the different examples above, store
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the RE object explicitly in a variable or use a temporary RE object. The
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examples below use one mode or the other arbitrarily. Either could correctly be
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used for any of these examples.
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.P
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You must supply extra pointer arguments to extract matched subpieces.
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.sp
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Example: extracts "ruby" into "s" and 1234 into "i"
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int i;
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string s;
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pcrecpp::RE re("(\e\ew+):(\e\ed+)");
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re.FullMatch("ruby:1234", &s, &i);
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.sp
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Example: does not try to extract any extra sub-patterns
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re.FullMatch("ruby:1234", &s);
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.sp
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Example: does not try to extract into NULL
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re.FullMatch("ruby:1234", NULL, &i);
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.sp
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Example: integer overflow causes failure
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!re.FullMatch("ruby:1234567891234", NULL, &i);
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.sp
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Example: fails because there aren't enough sub-patterns:
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!pcrecpp::RE("\e\ew+:\e\ed+").FullMatch("ruby:1234", &s);
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.sp
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Example: fails because string cannot be stored in integer
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!pcrecpp::RE("(.*)").FullMatch("ruby", &i);
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.sp
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The provided pointer arguments can be pointers to any scalar numeric
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type, or one of:
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.sp
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string (matched piece is copied to string)
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StringPiece (StringPiece is mutated to point to matched piece)
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T (where "bool T::ParseFrom(const char*, int)" exists)
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NULL (the corresponding matched sub-pattern is not copied)
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.sp
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The function returns true iff all of the following conditions are satisfied:
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.sp
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a. "text" matches "pattern" exactly;
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.sp
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b. The number of matched sub-patterns is >= number of supplied
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pointers;
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.sp
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c. The "i"th argument has a suitable type for holding the
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string captured as the "i"th sub-pattern. If you pass in
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void * NULL for the "i"th argument, or a non-void * NULL
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of the correct type, or pass fewer arguments than the
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number of sub-patterns, "i"th captured sub-pattern is
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ignored.
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.sp
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CAVEAT: An optional sub-pattern that does not exist in the matched
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string is assigned the empty string. Therefore, the following will
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return false (because the empty string is not a valid number):
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.sp
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int number;
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pcrecpp::RE::FullMatch("abc", "[a-z]+(\e\ed+)?", &number);
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.sp
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The matching interface supports at most 16 arguments per call.
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If you need more, consider using the more general interface
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\fBpcrecpp::RE::DoMatch\fP. See \fBpcrecpp.h\fP for the signature for
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\fBDoMatch\fP.
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.P
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NOTE: Do not use \fBno_arg\fP, which is used internally to mark the end of a
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list of optional arguments, as a placeholder for missing arguments, as this can
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lead to segfaults.
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.
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.
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.SH "QUOTING METACHARACTERS"
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.rs
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.sp
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You can use the "QuoteMeta" operation to insert backslashes before all
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potentially meaningful characters in a string. The returned string, used as a
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regular expression, will exactly match the original string.
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.sp
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Example:
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string quoted = RE::QuoteMeta(unquoted);
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.sp
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Note that it's legal to escape a character even if it has no special meaning in
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a regular expression -- so this function does that. (This also makes it
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identical to the perl function of the same name; see "perldoc -f quotemeta".)
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For example, "1.5-2.0?" becomes "1\e.5\e-2\e.0\e?".
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.
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.SH "PARTIAL MATCHES"
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.rs
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.sp
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You can use the "PartialMatch" operation when you want the pattern
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to match any substring of the text.
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.sp
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Example: simple search for a string:
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pcrecpp::RE("ell").PartialMatch("hello");
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.sp
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Example: find first number in a string:
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int number;
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pcrecpp::RE re("(\e\ed+)");
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re.PartialMatch("x*100 + 20", &number);
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assert(number == 100);
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.
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.
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.SH "UTF-8 AND THE MATCHING INTERFACE"
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.rs
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.sp
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By default, pattern and text are plain text, one byte per character. The UTF8
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flag, passed to the constructor, causes both pattern and string to be treated
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as UTF-8 text, still a byte stream but potentially multiple bytes per
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character. In practice, the text is likelier to be UTF-8 than the pattern, but
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the match returned may depend on the UTF8 flag, so always use it when matching
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UTF8 text. For example, "." will match one byte normally but with UTF8 set may
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match up to three bytes of a multi-byte character.
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.sp
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Example:
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pcrecpp::RE_Options options;
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options.set_utf8();
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pcrecpp::RE re(utf8_pattern, options);
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re.FullMatch(utf8_string);
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.sp
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Example: using the convenience function UTF8():
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pcrecpp::RE re(utf8_pattern, pcrecpp::UTF8());
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re.FullMatch(utf8_string);
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.sp
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NOTE: The UTF8 flag is ignored if pcre was not configured with the
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--enable-utf8 flag.
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.
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.
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.SH "PASSING MODIFIERS TO THE REGULAR EXPRESSION ENGINE"
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.rs
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.sp
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PCRE defines some modifiers to change the behavior of the regular expression
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engine. The C++ wrapper defines an auxiliary class, RE_Options, as a vehicle to
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pass such modifiers to a RE class. Currently, the following modifiers are
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supported:
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.sp
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modifier description Perl corresponding
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.sp
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PCRE_CASELESS case insensitive match /i
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PCRE_MULTILINE multiple lines match /m
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PCRE_DOTALL dot matches newlines /s
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PCRE_DOLLAR_ENDONLY $ matches only at end N/A
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PCRE_EXTRA strict escape parsing N/A
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PCRE_EXTENDED ignore white spaces /x
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PCRE_UTF8 handles UTF8 chars built-in
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PCRE_UNGREEDY reverses * and *? N/A
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PCRE_NO_AUTO_CAPTURE disables capturing parens N/A (*)
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.sp
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(*) Both Perl and PCRE allow non capturing parentheses by means of the
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"?:" modifier within the pattern itself. e.g. (?:ab|cd) does not
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capture, while (ab|cd) does.
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.P
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For a full account on how each modifier works, please check the
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PCRE API reference page.
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.P
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For each modifier, there are two member functions whose name is made
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out of the modifier in lowercase, without the "PCRE_" prefix. For
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instance, PCRE_CASELESS is handled by
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.sp
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bool caseless()
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.sp
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which returns true if the modifier is set, and
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.sp
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RE_Options & set_caseless(bool)
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.sp
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which sets or unsets the modifier. Moreover, PCRE_EXTRA_MATCH_LIMIT can be
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accessed through the \fBset_match_limit()\fP and \fBmatch_limit()\fP member
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functions. Setting \fImatch_limit\fP to a non-zero value will limit the
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execution of pcre to keep it from doing bad things like blowing the stack or
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taking an eternity to return a result. A value of 5000 is good enough to stop
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stack blowup in a 2MB thread stack. Setting \fImatch_limit\fP to zero disables
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match limiting. Alternatively, you can call \fBmatch_limit_recursion()\fP
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which uses PCRE_EXTRA_MATCH_LIMIT_RECURSION to limit how much PCRE
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recurses. \fBmatch_limit()\fP limits the number of matches PCRE does;
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\fBmatch_limit_recursion()\fP limits the depth of internal recursion, and
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therefore the amount of stack that is used.
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.P
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Normally, to pass one or more modifiers to a RE class, you declare
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a \fIRE_Options\fP object, set the appropriate options, and pass this
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object to a RE constructor. Example:
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.sp
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RE_Options opt;
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opt.set_caseless(true);
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if (RE("HELLO", opt).PartialMatch("hello world")) ...
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.sp
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RE_options has two constructors. The default constructor takes no arguments and
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creates a set of flags that are off by default. The optional parameter
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\fIoption_flags\fP is to facilitate transfer of legacy code from C programs.
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This lets you do
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.sp
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RE(pattern,
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RE_Options(PCRE_CASELESS|PCRE_MULTILINE)).PartialMatch(str);
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.sp
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However, new code is better off doing
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.sp
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RE(pattern,
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RE_Options().set_caseless(true).set_multiline(true))
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.PartialMatch(str);
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.sp
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If you are going to pass one of the most used modifiers, there are some
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convenience functions that return a RE_Options class with the
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appropriate modifier already set: \fBCASELESS()\fP, \fBUTF8()\fP,
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\fBMULTILINE()\fP, \fBDOTALL\fP(), and \fBEXTENDED()\fP.
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.P
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If you need to set several options at once, and you don't want to go through
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the pains of declaring a RE_Options object and setting several options, there
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is a parallel method that give you such ability on the fly. You can concatenate
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several \fBset_xxxxx()\fP member functions, since each of them returns a
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reference to its class object. For example, to pass PCRE_CASELESS,
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PCRE_EXTENDED, and PCRE_MULTILINE to a RE with one statement, you may write:
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.sp
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RE(" ^ xyz \e\es+ .* blah$",
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RE_Options()
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.set_caseless(true)
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.set_extended(true)
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.set_multiline(true)).PartialMatch(sometext);
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.sp
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.
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.
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.SH "SCANNING TEXT INCREMENTALLY"
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.rs
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.sp
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The "Consume" operation may be useful if you want to repeatedly
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match regular expressions at the front of a string and skip over
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them as they match. This requires use of the "StringPiece" type,
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which represents a sub-range of a real string. Like RE, StringPiece
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is defined in the pcrecpp namespace.
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.sp
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Example: read lines of the form "var = value" from a string.
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string contents = ...; // Fill string somehow
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pcrecpp::StringPiece input(contents); // Wrap in a StringPiece
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.sp
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string var;
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int value;
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pcrecpp::RE re("(\e\ew+) = (\e\ed+)\en");
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while (re.Consume(&input, &var, &value)) {
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...;
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}
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.sp
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Each successful call to "Consume" will set "var/value", and also
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advance "input" so it points past the matched text.
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.P
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The "FindAndConsume" operation is similar to "Consume" but does not
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anchor your match at the beginning of the string. For example, you
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could extract all words from a string by repeatedly calling
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.sp
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pcrecpp::RE("(\e\ew+)").FindAndConsume(&input, &word)
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.
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.
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.SH "PARSING HEX/OCTAL/C-RADIX NUMBERS"
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.rs
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.sp
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By default, if you pass a pointer to a numeric value, the
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corresponding text is interpreted as a base-10 number. You can
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instead wrap the pointer with a call to one of the operators Hex(),
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Octal(), or CRadix() to interpret the text in another base. The
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CRadix operator interprets C-style "0" (base-8) and "0x" (base-16)
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prefixes, but defaults to base-10.
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.sp
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Example:
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int a, b, c, d;
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pcrecpp::RE re("(.*) (.*) (.*) (.*)");
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re.FullMatch("100 40 0100 0x40",
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pcrecpp::Octal(&a), pcrecpp::Hex(&b),
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pcrecpp::CRadix(&c), pcrecpp::CRadix(&d));
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.sp
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will leave 64 in a, b, c, and d.
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.
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.
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.SH "REPLACING PARTS OF STRINGS"
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.rs
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.sp
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You can replace the first match of "pattern" in "str" with "rewrite".
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Within "rewrite", backslash-escaped digits (\e1 to \e9) can be
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used to insert text matching corresponding parenthesized group
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from the pattern. \e0 in "rewrite" refers to the entire matching
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text. For example:
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.sp
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string s = "yabba dabba doo";
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pcrecpp::RE("b+").Replace("d", &s);
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.sp
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will leave "s" containing "yada dabba doo". The result is true if the pattern
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matches and a replacement occurs, false otherwise.
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.P
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\fBGlobalReplace\fP is like \fBReplace\fP except that it replaces all
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occurrences of the pattern in the string with the rewrite. Replacements are
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not subject to re-matching. For example:
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.sp
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string s = "yabba dabba doo";
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pcrecpp::RE("b+").GlobalReplace("d", &s);
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.sp
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will leave "s" containing "yada dada doo". It returns the number of
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replacements made.
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.P
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\fBExtract\fP is like \fBReplace\fP, except that if the pattern matches,
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"rewrite" is copied into "out" (an additional argument) with substitutions.
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The non-matching portions of "text" are ignored. Returns true iff a match
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occurred and the extraction happened successfully; if no match occurs, the
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string is left unaffected.
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.
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.
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.SH AUTHOR
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.rs
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.sp
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.nf
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The C++ wrapper was contributed by Google Inc.
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Copyright (c) 2007 Google Inc.
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.fi
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.
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.
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.SH REVISION
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.rs
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.sp
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.nf
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Last updated: 08 January 2012
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.fi
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