PCRECPP(3) Library Functions Manual PCRECPP(3)
PCRE - Perl-compatible regular expressions.
#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 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.
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\?".
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);
NOTE: The UTF8 flag is ignored if pcre was not configured with
the
--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 (*)
(*) 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);
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)
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.
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.
The C++ wrapper was contributed by Google Inc.
Copyright (c) 2007 Google Inc.
Last updated: 08 January 2012
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-8.45.tar.gz fetched from
⟨ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/⟩ on
2021-08-27. If you discover any rendering problems in this HTML
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improvements to the information in this COLOPHON (which is not
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man-pages@man7.org
PCRE 8.30 08 January 2012 PCRECPP(3)
Pages that refer to this page: pcreapi(3)
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