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Tue Mar 17 10:58:16 2009 UTC (12 years, 6 months ago) by ph10
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Comments about no_arg in the C++ wrapper.
3 PCRE - Perl-compatible regular expressions.
5 .rs
6 .sp
7 .B #include <pcrecpp.h>
8 .
10 .rs
11 .sp
12 The C++ wrapper for PCRE was provided by Google Inc. Some additional
13 functionality was added by Giuseppe Maxia. This brief man page was constructed
14 from the notes in the \fIpcrecpp.h\fP file, which should be consulted for
15 further details.
16 .
17 .
19 .rs
20 .sp
21 The "FullMatch" operation checks that supplied text matches a supplied pattern
22 exactly. If pointer arguments are supplied, it copies matched sub-strings that
23 match sub-patterns into them.
24 .sp
25 Example: successful match
26 pcrecpp::RE re("h.*o");
27 re.FullMatch("hello");
28 .sp
29 Example: unsuccessful match (requires full match):
30 pcrecpp::RE re("e");
31 !re.FullMatch("hello");
32 .sp
33 Example: creating a temporary RE object:
34 pcrecpp::RE("h.*o").FullMatch("hello");
35 .sp
36 You can pass in a "const char*" or a "string" for "text". The examples below
37 tend to use a const char*. You can, as in the different examples above, store
38 the RE object explicitly in a variable or use a temporary RE object. The
39 examples below use one mode or the other arbitrarily. Either could correctly be
40 used for any of these examples.
41 .P
42 You must supply extra pointer arguments to extract matched subpieces.
43 .sp
44 Example: extracts "ruby" into "s" and 1234 into "i"
45 int i;
46 string s;
47 pcrecpp::RE re("(\e\ew+):(\e\ed+)");
48 re.FullMatch("ruby:1234", &s, &i);
49 .sp
50 Example: does not try to extract any extra sub-patterns
51 re.FullMatch("ruby:1234", &s);
52 .sp
53 Example: does not try to extract into NULL
54 re.FullMatch("ruby:1234", NULL, &i);
55 .sp
56 Example: integer overflow causes failure
57 !re.FullMatch("ruby:1234567891234", NULL, &i);
58 .sp
59 Example: fails because there aren't enough sub-patterns:
60 !pcrecpp::RE("\e\ew+:\e\ed+").FullMatch("ruby:1234", &s);
61 .sp
62 Example: fails because string cannot be stored in integer
63 !pcrecpp::RE("(.*)").FullMatch("ruby", &i);
64 .sp
65 The provided pointer arguments can be pointers to any scalar numeric
66 type, or one of:
67 .sp
68 string (matched piece is copied to string)
69 StringPiece (StringPiece is mutated to point to matched piece)
70 T (where "bool T::ParseFrom(const char*, int)" exists)
71 NULL (the corresponding matched sub-pattern is not copied)
72 .sp
73 The function returns true iff all of the following conditions are satisfied:
74 .sp
75 a. "text" matches "pattern" exactly;
76 .sp
77 b. The number of matched sub-patterns is >= number of supplied
78 pointers;
79 .sp
80 c. The "i"th argument has a suitable type for holding the
81 string captured as the "i"th sub-pattern. If you pass in
82 void * NULL for the "i"th argument, or a non-void * NULL
83 of the correct type, or pass fewer arguments than the
84 number of sub-patterns, "i"th captured sub-pattern is
85 ignored.
86 .sp
87 CAVEAT: An optional sub-pattern that does not exist in the matched
88 string is assigned the empty string. Therefore, the following will
89 return false (because the empty string is not a valid number):
90 .sp
91 int number;
92 pcrecpp::RE::FullMatch("abc", "[a-z]+(\e\ed+)?", &number);
93 .sp
94 The matching interface supports at most 16 arguments per call.
95 If you need more, consider using the more general interface
96 \fBpcrecpp::RE::DoMatch\fP. See \fBpcrecpp.h\fP for the signature for
97 \fBDoMatch\fP.
98 .P
99 NOTE: Do not use \fBno_arg\fP, which is used internally to mark the end of a
100 list of optional arguments, as a placeholder for missing arguments, as this can
101 lead to segfaults.
102 .
103 .
105 .rs
106 .sp
107 You can use the "QuoteMeta" operation to insert backslashes before all
108 potentially meaningful characters in a string. The returned string, used as a
109 regular expression, will exactly match the original string.
110 .sp
111 Example:
112 string quoted = RE::QuoteMeta(unquoted);
113 .sp
114 Note that it's legal to escape a character even if it has no special meaning in
115 a regular expression -- so this function does that. (This also makes it
116 identical to the perl function of the same name; see "perldoc -f quotemeta".)
117 For example, "1.5-2.0?" becomes "1\e.5\e-2\e.0\e?".
118 .
120 .rs
121 .sp
122 You can use the "PartialMatch" operation when you want the pattern
123 to match any substring of the text.
124 .sp
125 Example: simple search for a string:
126 pcrecpp::RE("ell").PartialMatch("hello");
127 .sp
128 Example: find first number in a string:
129 int number;
130 pcrecpp::RE re("(\e\ed+)");
131 re.PartialMatch("x*100 + 20", &number);
132 assert(number == 100);
133 .
134 .
136 .rs
137 .sp
138 By default, pattern and text are plain text, one byte per character. The UTF8
139 flag, passed to the constructor, causes both pattern and string to be treated
140 as UTF-8 text, still a byte stream but potentially multiple bytes per
141 character. In practice, the text is likelier to be UTF-8 than the pattern, but
142 the match returned may depend on the UTF8 flag, so always use it when matching
143 UTF8 text. For example, "." will match one byte normally but with UTF8 set may
144 match up to three bytes of a multi-byte character.
145 .sp
146 Example:
147 pcrecpp::RE_Options options;
148 options.set_utf8();
149 pcrecpp::RE re(utf8_pattern, options);
150 re.FullMatch(utf8_string);
151 .sp
152 Example: using the convenience function UTF8():
153 pcrecpp::RE re(utf8_pattern, pcrecpp::UTF8());
154 re.FullMatch(utf8_string);
155 .sp
156 NOTE: The UTF8 flag is ignored if pcre was not configured with the
157 --enable-utf8 flag.
158 .
159 .
161 .rs
162 .sp
163 PCRE defines some modifiers to change the behavior of the regular expression
164 engine. The C++ wrapper defines an auxiliary class, RE_Options, as a vehicle to
165 pass such modifiers to a RE class. Currently, the following modifiers are
166 supported:
167 .sp
168 modifier description Perl corresponding
169 .sp
170 PCRE_CASELESS case insensitive match /i
171 PCRE_MULTILINE multiple lines match /m
172 PCRE_DOTALL dot matches newlines /s
173 PCRE_DOLLAR_ENDONLY $ matches only at end N/A
174 PCRE_EXTRA strict escape parsing N/A
175 PCRE_EXTENDED ignore whitespaces /x
176 PCRE_UTF8 handles UTF8 chars built-in
177 PCRE_UNGREEDY reverses * and *? N/A
178 PCRE_NO_AUTO_CAPTURE disables capturing parens N/A (*)
179 .sp
180 (*) Both Perl and PCRE allow non capturing parentheses by means of the
181 "?:" modifier within the pattern itself. e.g. (?:ab|cd) does not
182 capture, while (ab|cd) does.
183 .P
184 For a full account on how each modifier works, please check the
185 PCRE API reference page.
186 .P
187 For each modifier, there are two member functions whose name is made
188 out of the modifier in lowercase, without the "PCRE_" prefix. For
189 instance, PCRE_CASELESS is handled by
190 .sp
191 bool caseless()
192 .sp
193 which returns true if the modifier is set, and
194 .sp
195 RE_Options & set_caseless(bool)
196 .sp
197 which sets or unsets the modifier. Moreover, PCRE_EXTRA_MATCH_LIMIT can be
198 accessed through the \fBset_match_limit()\fR and \fBmatch_limit()\fR member
199 functions. Setting \fImatch_limit\fR to a non-zero value will limit the
200 execution of pcre to keep it from doing bad things like blowing the stack or
201 taking an eternity to return a result. A value of 5000 is good enough to stop
202 stack blowup in a 2MB thread stack. Setting \fImatch_limit\fR to zero disables
203 match limiting. Alternatively, you can call \fBmatch_limit_recursion()\fP
204 which uses PCRE_EXTRA_MATCH_LIMIT_RECURSION to limit how much PCRE
205 recurses. \fBmatch_limit()\fP limits the number of matches PCRE does;
206 \fBmatch_limit_recursion()\fP limits the depth of internal recursion, and
207 therefore the amount of stack that is used.
208 .P
209 Normally, to pass one or more modifiers to a RE class, you declare
210 a \fIRE_Options\fR object, set the appropriate options, and pass this
211 object to a RE constructor. Example:
212 .sp
213 RE_options opt;
214 opt.set_caseless(true);
215 if (RE("HELLO", opt).PartialMatch("hello world")) ...
216 .sp
217 RE_options has two constructors. The default constructor takes no arguments and
218 creates a set of flags that are off by default. The optional parameter
219 \fIoption_flags\fR is to facilitate transfer of legacy code from C programs.
220 This lets you do
221 .sp
222 RE(pattern,
223 RE_Options(PCRE_CASELESS|PCRE_MULTILINE)).PartialMatch(str);
224 .sp
225 However, new code is better off doing
226 .sp
227 RE(pattern,
228 RE_Options().set_caseless(true).set_multiline(true))
229 .PartialMatch(str);
230 .sp
231 If you are going to pass one of the most used modifiers, there are some
232 convenience functions that return a RE_Options class with the
233 appropriate modifier already set: \fBCASELESS()\fR, \fBUTF8()\fR,
234 \fBMULTILINE()\fR, \fBDOTALL\fR(), and \fBEXTENDED()\fR.
235 .P
236 If you need to set several options at once, and you don't want to go through
237 the pains of declaring a RE_Options object and setting several options, there
238 is a parallel method that give you such ability on the fly. You can concatenate
239 several \fBset_xxxxx()\fR member functions, since each of them returns a
240 reference to its class object. For example, to pass PCRE_CASELESS,
241 PCRE_EXTENDED, and PCRE_MULTILINE to a RE with one statement, you may write:
242 .sp
243 RE(" ^ xyz \e\es+ .* blah$",
244 RE_Options()
245 .set_caseless(true)
246 .set_extended(true)
247 .set_multiline(true)).PartialMatch(sometext);
248 .sp
249 .
250 .
252 .rs
253 .sp
254 The "Consume" operation may be useful if you want to repeatedly
255 match regular expressions at the front of a string and skip over
256 them as they match. This requires use of the "StringPiece" type,
257 which represents a sub-range of a real string. Like RE, StringPiece
258 is defined in the pcrecpp namespace.
259 .sp
260 Example: read lines of the form "var = value" from a string.
261 string contents = ...; // Fill string somehow
262 pcrecpp::StringPiece input(contents); // Wrap in a StringPiece
264 string var;
265 int value;
266 pcrecpp::RE re("(\e\ew+) = (\e\ed+)\en");
267 while (re.Consume(&input, &var, &value)) {
268 ...;
269 }
270 .sp
271 Each successful call to "Consume" will set "var/value", and also
272 advance "input" so it points past the matched text.
273 .P
274 The "FindAndConsume" operation is similar to "Consume" but does not
275 anchor your match at the beginning of the string. For example, you
276 could extract all words from a string by repeatedly calling
277 .sp
278 pcrecpp::RE("(\e\ew+)").FindAndConsume(&input, &word)
279 .
280 .
282 .rs
283 .sp
284 By default, if you pass a pointer to a numeric value, the
285 corresponding text is interpreted as a base-10 number. You can
286 instead wrap the pointer with a call to one of the operators Hex(),
287 Octal(), or CRadix() to interpret the text in another base. The
288 CRadix operator interprets C-style "0" (base-8) and "0x" (base-16)
289 prefixes, but defaults to base-10.
290 .sp
291 Example:
292 int a, b, c, d;
293 pcrecpp::RE re("(.*) (.*) (.*) (.*)");
294 re.FullMatch("100 40 0100 0x40",
295 pcrecpp::Octal(&a), pcrecpp::Hex(&b),
296 pcrecpp::CRadix(&c), pcrecpp::CRadix(&d));
297 .sp
298 will leave 64 in a, b, c, and d.
299 .
300 .
302 .rs
303 .sp
304 You can replace the first match of "pattern" in "str" with "rewrite".
305 Within "rewrite", backslash-escaped digits (\e1 to \e9) can be
306 used to insert text matching corresponding parenthesized group
307 from the pattern. \e0 in "rewrite" refers to the entire matching
308 text. For example:
309 .sp
310 string s = "yabba dabba doo";
311 pcrecpp::RE("b+").Replace("d", &s);
312 .sp
313 will leave "s" containing "yada dabba doo". The result is true if the pattern
314 matches and a replacement occurs, false otherwise.
315 .P
316 \fBGlobalReplace\fP is like \fBReplace\fP except that it replaces all
317 occurrences of the pattern in the string with the rewrite. Replacements are
318 not subject to re-matching. For example:
319 .sp
320 string s = "yabba dabba doo";
321 pcrecpp::RE("b+").GlobalReplace("d", &s);
322 .sp
323 will leave "s" containing "yada dada doo". It returns the number of
324 replacements made.
325 .P
326 \fBExtract\fP is like \fBReplace\fP, except that if the pattern matches,
327 "rewrite" is copied into "out" (an additional argument) with substitutions.
328 The non-matching portions of "text" are ignored. Returns true iff a match
329 occurred and the extraction happened successfully; if no match occurs, the
330 string is left unaffected.
331 .
332 .
334 .rs
335 .sp
336 .nf
337 The C++ wrapper was contributed by Google Inc.
338 Copyright (c) 2007 Google Inc.
339 .fi
340 .
341 .
343 .rs
344 .sp
345 .nf
346 Last updated: 17 March 2009
347 .fi


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