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3 PCRE - Perl-compatible regular expressions.
5 .rs
6 .sp
7 .B #include <pcrecpp.h>
8 .PP
9 .SM
10 .br
12 .rs
13 .sp
14 The C++ wrapper for PCRE was provided by Google Inc. Some additional
15 functionality was added by Giuseppe Maxia. This brief man page was constructed
16 from the notes in the \fIpcrecpp.h\fP file, which should be consulted for
17 further details.
18 .
19 .
21 .rs
22 .sp
23 The "FullMatch" operation checks that supplied text matches a supplied pattern
24 exactly. If pointer arguments are supplied, it copies matched sub-strings that
25 match sub-patterns into them.
26 .sp
27 Example: successful match
28 pcrecpp::RE re("h.*o");
29 re.FullMatch("hello");
30 .sp
31 Example: unsuccessful match (requires full match):
32 pcrecpp::RE re("e");
33 !re.FullMatch("hello");
34 .sp
35 Example: creating a temporary RE object:
36 pcrecpp::RE("h.*o").FullMatch("hello");
37 .sp
38 You can pass in a "const char*" or a "string" for "text". The examples below
39 tend to use a const char*. You can, as in the different examples above, store
40 the RE object explicitly in a variable or use a temporary RE object. The
41 examples below use one mode or the other arbitrarily. Either could correctly be
42 used for any of these examples.
43 .P
44 You must supply extra pointer arguments to extract matched subpieces.
45 .sp
46 Example: extracts "ruby" into "s" and 1234 into "i"
47 int i;
48 string s;
49 pcrecpp::RE re("(\e\ew+):(\e\ed+)");
50 re.FullMatch("ruby:1234", &s, &i);
51 .sp
52 Example: does not try to extract any extra sub-patterns
53 re.FullMatch("ruby:1234", &s);
54 .sp
55 Example: does not try to extract into NULL
56 re.FullMatch("ruby:1234", NULL, &i);
57 .sp
58 Example: integer overflow causes failure
59 !re.FullMatch("ruby:1234567891234", NULL, &i);
60 .sp
61 Example: fails because there aren't enough sub-patterns:
62 !pcrecpp::RE("\e\ew+:\e\ed+").FullMatch("ruby:1234", &s);
63 .sp
64 Example: fails because string cannot be stored in integer
65 !pcrecpp::RE("(.*)").FullMatch("ruby", &i);
66 .sp
67 The provided pointer arguments can be pointers to any scalar numeric
68 type, or one of:
69 .sp
70 string (matched piece is copied to string)
71 StringPiece (StringPiece is mutated to point to matched piece)
72 T (where "bool T::ParseFrom(const char*, int)" exists)
73 NULL (the corresponding matched sub-pattern is not copied)
74 .sp
75 The function returns true iff all of the following conditions are satisfied:
76 .sp
77 a. "text" matches "pattern" exactly;
78 .sp
79 b. The number of matched sub-patterns is >= number of supplied
80 pointers;
81 .sp
82 c. The "i"th argument has a suitable type for holding the
83 string captured as the "i"th sub-pattern. If you pass in
84 NULL for the "i"th argument, or pass fewer arguments than
85 number of sub-patterns, "i"th captured sub-pattern is
86 ignored.
87 .sp
88 CAVEAT: An optional sub-pattern that does not exist in the matched
89 string is assigned the empty string. Therefore, the following will
90 return false (because the empty string is not a valid number):
91 .sp
92 int number;
93 pcrecpp::RE::FullMatch("abc", "[a-z]+(\\d+)?", &number);
94 .sp
95 The matching interface supports at most 16 arguments per call.
96 If you need more, consider using the more general interface
97 \fBpcrecpp::RE::DoMatch\fP. See \fBpcrecpp.h\fP for the signature for
98 \fBDoMatch\fP.
99 .
101 .rs
102 .sp
103 You can use the "QuoteMeta" operation to insert backslashes before all
104 potentially meaningful characters in a string. The returned string, used as a
105 regular expression, will exactly match the original string.
106 .sp
107 Example:
108 string quoted = RE::QuoteMeta(unquoted);
109 .sp
110 Note that it's legal to escape a character even if it has no special meaning in
111 a regular expression -- so this function does that. (This also makes it
112 identical to the perl function of the same name; see "perldoc -f quotemeta".)
113 For example, "1.5-2.0?" becomes "1\e.5\e-2\e.0\e?".
114 .
116 .rs
117 .sp
118 You can use the "PartialMatch" operation when you want the pattern
119 to match any substring of the text.
120 .sp
121 Example: simple search for a string:
122 pcrecpp::RE("ell").PartialMatch("hello");
123 .sp
124 Example: find first number in a string:
125 int number;
126 pcrecpp::RE re("(\e\ed+)");
127 re.PartialMatch("x*100 + 20", &number);
128 assert(number == 100);
129 .
130 .
132 .rs
133 .sp
134 By default, pattern and text are plain text, one byte per character. The UTF8
135 flag, passed to the constructor, causes both pattern and string to be treated
136 as UTF-8 text, still a byte stream but potentially multiple bytes per
137 character. In practice, the text is likelier to be UTF-8 than the pattern, but
138 the match returned may depend on the UTF8 flag, so always use it when matching
139 UTF8 text. For example, "." will match one byte normally but with UTF8 set may
140 match up to three bytes of a multi-byte character.
141 .sp
142 Example:
143 pcrecpp::RE_Options options;
144 options.set_utf8();
145 pcrecpp::RE re(utf8_pattern, options);
146 re.FullMatch(utf8_string);
147 .sp
148 Example: using the convenience function UTF8():
149 pcrecpp::RE re(utf8_pattern, pcrecpp::UTF8());
150 re.FullMatch(utf8_string);
151 .sp
152 NOTE: The UTF8 flag is ignored if pcre was not configured with the
153 --enable-utf8 flag.
154 .
155 .
157 .rs
158 .sp
159 PCRE defines some modifiers to change the behavior of the regular expression
160 engine. The C++ wrapper defines an auxiliary class, RE_Options, as a vehicle to
161 pass such modifiers to a RE class. Currently, the following modifiers are
162 supported:
163 .sp
164 modifier description Perl corresponding
165 .sp
166 PCRE_CASELESS case insensitive match /i
167 PCRE_MULTILINE multiple lines match /m
168 PCRE_DOTALL dot matches newlines /s
169 PCRE_DOLLAR_ENDONLY $ matches only at end N/A
170 PCRE_EXTRA strict escape parsing N/A
171 PCRE_EXTENDED ignore whitespaces /x
172 PCRE_UTF8 handles UTF8 chars built-in
173 PCRE_UNGREEDY reverses * and *? N/A
174 PCRE_NO_AUTO_CAPTURE disables capturing parens N/A (*)
175 .sp
176 (*) Both Perl and PCRE allow non capturing parentheses by means of the
177 "?:" modifier within the pattern itself. e.g. (?:ab|cd) does not
178 capture, while (ab|cd) does.
179 .P
180 For a full account on how each modifier works, please check the
181 PCRE API reference page.
182 .P
183 For each modifier, there are two member functions whose name is made
184 out of the modifier in lowercase, without the "PCRE_" prefix. For
185 instance, PCRE_CASELESS is handled by
186 .sp
187 bool caseless()
188 .sp
189 which returns true if the modifier is set, and
190 .sp
191 RE_Options & set_caseless(bool)
192 .sp
193 which sets or unsets the modifier. Moreover, PCRE_EXTRA_MATCH_LIMIT can be
194 accessed through the \fBset_match_limit()\fR and \fBmatch_limit()\fR member
195 functions. Setting \fImatch_limit\fR to a non-zero value will limit the
196 execution of pcre to keep it from doing bad things like blowing the stack or
197 taking an eternity to return a result. A value of 5000 is good enough to stop
198 stack blowup in a 2MB thread stack. Setting \fImatch_limit\fR to zero disables
199 match limiting. Alternatively, you can call \fBmatch_limit_recursion()\fP
200 which uses PCRE_EXTRA_MATCH_LIMIT_RECURSION to limit how much PCRE
201 recurses. \fBmatch_limit()\fP limits the number of matches PCRE does;
202 \fBmatch_limit_recursion()\fP limits the depth of internal recursion, and
203 therefore the amount of stack that is used.
204 .P
205 Normally, to pass one or more modifiers to a RE class, you declare
206 a \fIRE_Options\fR object, set the appropriate options, and pass this
207 object to a RE constructor. Example:
208 .sp
209 RE_options opt;
210 opt.set_caseless(true);
211 if (RE("HELLO", opt).PartialMatch("hello world")) ...
212 .sp
213 RE_options has two constructors. The default constructor takes no arguments and
214 creates a set of flags that are off by default. The optional parameter
215 \fIoption_flags\fR is to facilitate transfer of legacy code from C programs.
216 This lets you do
217 .sp
218 RE(pattern,
219 RE_Options(PCRE_CASELESS|PCRE_MULTILINE)).PartialMatch(str);
220 .sp
221 However, new code is better off doing
222 .sp
223 RE(pattern,
224 RE_Options().set_caseless(true).set_multiline(true))
225 .PartialMatch(str);
226 .sp
227 If you are going to pass one of the most used modifiers, there are some
228 convenience functions that return a RE_Options class with the
229 appropriate modifier already set: \fBCASELESS()\fR, \fBUTF8()\fR,
230 \fBMULTILINE()\fR, \fBDOTALL\fR(), and \fBEXTENDED()\fR.
231 .P
232 If you need to set several options at once, and you don't want to go through
233 the pains of declaring a RE_Options object and setting several options, there
234 is a parallel method that give you such ability on the fly. You can concatenate
235 several \fBset_xxxxx()\fR member functions, since each of them returns a
236 reference to its class object. For example, to pass PCRE_CASELESS,
237 PCRE_EXTENDED, and PCRE_MULTILINE to a RE with one statement, you may write:
238 .sp
239 RE(" ^ xyz \e\es+ .* blah$",
240 RE_Options()
241 .set_caseless(true)
242 .set_extended(true)
243 .set_multiline(true)).PartialMatch(sometext);
244 .sp
245 .
246 .
248 .rs
249 .sp
250 The "Consume" operation may be useful if you want to repeatedly
251 match regular expressions at the front of a string and skip over
252 them as they match. This requires use of the "StringPiece" type,
253 which represents a sub-range of a real string. Like RE, StringPiece
254 is defined in the pcrecpp namespace.
255 .sp
256 Example: read lines of the form "var = value" from a string.
257 string contents = ...; // Fill string somehow
258 pcrecpp::StringPiece input(contents); // Wrap in a StringPiece
260 string var;
261 int value;
262 pcrecpp::RE re("(\e\ew+) = (\e\ed+)\en");
263 while (re.Consume(&input, &var, &value)) {
264 ...;
265 }
266 .sp
267 Each successful call to "Consume" will set "var/value", and also
268 advance "input" so it points past the matched text.
269 .P
270 The "FindAndConsume" operation is similar to "Consume" but does not
271 anchor your match at the beginning of the string. For example, you
272 could extract all words from a string by repeatedly calling
273 .sp
274 pcrecpp::RE("(\e\ew+)").FindAndConsume(&input, &word)
275 .
276 .
278 .rs
279 .sp
280 By default, if you pass a pointer to a numeric value, the
281 corresponding text is interpreted as a base-10 number. You can
282 instead wrap the pointer with a call to one of the operators Hex(),
283 Octal(), or CRadix() to interpret the text in another base. The
284 CRadix operator interprets C-style "0" (base-8) and "0x" (base-16)
285 prefixes, but defaults to base-10.
286 .sp
287 Example:
288 int a, b, c, d;
289 pcrecpp::RE re("(.*) (.*) (.*) (.*)");
290 re.FullMatch("100 40 0100 0x40",
291 pcrecpp::Octal(&a), pcrecpp::Hex(&b),
292 pcrecpp::CRadix(&c), pcrecpp::CRadix(&d));
293 .sp
294 will leave 64 in a, b, c, and d.
295 .
296 .
298 .rs
299 .sp
300 You can replace the first match of "pattern" in "str" with "rewrite".
301 Within "rewrite", backslash-escaped digits (\e1 to \e9) can be
302 used to insert text matching corresponding parenthesized group
303 from the pattern. \e0 in "rewrite" refers to the entire matching
304 text. For example:
305 .sp
306 string s = "yabba dabba doo";
307 pcrecpp::RE("b+").Replace("d", &s);
308 .sp
309 will leave "s" containing "yada dabba doo". The result is true if the pattern
310 matches and a replacement occurs, false otherwise.
311 .P
312 \fBGlobalReplace\fP is like \fBReplace\fP except that it replaces all
313 occurrences of the pattern in the string with the rewrite. Replacements are
314 not subject to re-matching. For example:
315 .sp
316 string s = "yabba dabba doo";
317 pcrecpp::RE("b+").GlobalReplace("d", &s);
318 .sp
319 will leave "s" containing "yada dada doo". It returns the number of
320 replacements made.
321 .P
322 \fBExtract\fP is like \fBReplace\fP, except that if the pattern matches,
323 "rewrite" is copied into "out" (an additional argument) with substitutions.
324 The non-matching portions of "text" are ignored. Returns true iff a match
325 occurred and the extraction happened successfully; if no match occurs, the
326 string is left unaffected.
327 .
328 .
330 .rs
331 .sp
332 The C++ wrapper was contributed by Google Inc.
333 .br
334 Copyright (c) 2006 Google Inc.

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