1/*************************************************
2* PCRE2 DEMONSTRATION PROGRAM *
3*************************************************/
4/* This is a demonstration program to illustrate a straightforward way of
6using the PCRE2 regular expression library from a C program. See the
7pcre2sample documentation for a short discussion ("man pcre2sample" if you have
8the PCRE2 man pages installed). PCRE2 is a revised API for the library, and is
9incompatible with the original PCRE API.
10There are actually three libraries, each supporting a different code unit
12width. This demonstration program uses the 8‐bit library. The default is to
13process each code unit as a separate character, but if the pattern begins with
14"(*UTF)", both it and the subject are treated as UTF‐8 strings, where
15characters may occupy multiple code units.
16In Unix‐like environments, if PCRE2 is installed in your standard system
18libraries, you should be able to compile this program using this command:
19cc ‐Wall pcre2demo.c ‐lpcre2‐8 ‐o pcre2demo
21If PCRE2 is not installed in a standard place, it is likely to be installed
23with support for the pkg‐config mechanism. If you have pkg‐config, you can
24compile this program using this command:
25cc ‐Wall pcre2demo.c ‘pkg‐config ‐‐cflags ‐‐libs libpcre2‐8‘ ‐o pcre2demo
27If you do not have pkg‐config, you may have to use something like this:
29cc ‐Wall pcre2demo.c ‐I/usr/local/include ‐L/usr/local/lib \
31 ‐R/usr/local/lib ‐lpcre2‐8 ‐o pcre2demo
32Replace "/usr/local/include" and "/usr/local/lib" with wherever the include and
34library files for PCRE2 are installed on your system. Only some operating
35systems (Solaris is one) use the ‐R option.
36Building under Windows:
38If you want to statically link this program against a non‐dll .a file, you must
40define PCRE2_STATIC before including pcre2.h, so in this environment, uncomment
41the following line. */
42/* #define PCRE2_STATIC */
44/* The PCRE2_CODE_UNIT_WIDTH macro must be defined before including pcre2.h.
46For a program that uses only one code unit width, setting it to 8, 16, or 32
47makes it possible to use generic function names such as pcre2_compile(). Note
48that just changing 8 to 16 (for example) is not sufficient to convert this
49program to process 16‐bit characters. Even in a fully 16‐bit environment, where
50string‐handling functions such as strcmp() and printf() work with 16‐bit
51characters, the code for handling the table of named substrings will still need
52to be modified. */
53#define PCRE2_CODE_UNIT_WIDTH 8
55#include <stdio.h>
57#include <string.h>
58#include <pcre2.h>
59/**************************************************************************
62* Here is the program. The API includes the concept of "contexts" for *
63* setting up unusual interface requirements for compiling and matching, *
64* such as custom memory managers and non‐standard newline definitions. *
65* This program does not do any of this, so it makes no use of contexts, *
66* always passing NULL where a context could be given. *
67**************************************************************************/
68int main(int argc, char **argv)
70{
71pcre2_code *re;
72PCRE2_SPTR pattern; /* PCRE2_SPTR is a pointer to unsigned code units of */
73PCRE2_SPTR subject; /* the appropriate width (in this case, 8 bits). */
74PCRE2_SPTR name_table;
75int crlf_is_newline;
77int errornumber;
78int find_all;
79int i;
80int rc;
81int utf8;
82uint32_t option_bits;
84uint32_t namecount;
85uint32_t name_entry_size;
86uint32_t newline;
87PCRE2_SIZE erroroffset;
89PCRE2_SIZE *ovector;
90PCRE2_SIZE subject_length;
91pcre2_match_data *match_data;
93/**************************************************************************
96* First, sort out the command line. There is only one possible option at *
97* the moment, "‐g" to request repeated matching to find all occurrences, *
98* like Perl’s /g option. We set the variable find_all to a non‐zero value *
99* if the ‐g option is present. *
100**************************************************************************/
101find_all = 0;
103for (i = 1; i < argc; i++)
104 {
105 if (strcmp(argv[i], "‐g") == 0) find_all = 1;
106 else if (argv[i][0] == ’‐’)
107 {
108 printf("Unrecognised option %s\n", argv[i]);
109 return 1;
110 }
111 else break;
112 }
113/* After the options, we require exactly two arguments, which are the pattern,
115and the subject string. */
116if (argc ‐ i != 2)
118 {
119 printf("Exactly two arguments required: a regex and a subject string\n");
120 return 1;
121 }
122/* Pattern and subject are char arguments, so they can be straightforwardly
124cast to PCRE2_SPTR because we are working in 8‐bit code units. The subject
125length is cast to PCRE2_SIZE for completeness, though PCRE2_SIZE is in fact
126defined to be size_t. */
127pattern = (PCRE2_SPTR)argv[i];
129subject = (PCRE2_SPTR)argv[i+1];
130subject_length = (PCRE2_SIZE)strlen((char *)subject);
131/*************************************************************************
134* Now we are going to compile the regular expression pattern, and handle *
135* any errors that are detected. *
136*************************************************************************/
137re = pcre2_compile(
139 pattern, /* the pattern */
140 PCRE2_ZERO_TERMINATED, /* indicates pattern is zero‐terminated */
141 0, /* default options */
142 &errornumber, /* for error number */
143 &erroroffset, /* for error offset */
144 NULL); /* use default compile context */
145/* Compilation failed: print the error message and exit. */
147if (re == NULL)
149 {
150 PCRE2_UCHAR buffer[256];
151 pcre2_get_error_message(errornumber, buffer, sizeof(buffer));
152 printf("PCRE2 compilation failed at offset %d: %s\n", (int)erroroffset,
153 buffer);
154 return 1;
155 }
156/*************************************************************************
159* If the compilation succeeded, we call PCRE2 again, in order to do a *
160* pattern match against the subject string. This does just ONE match. If *
161* further matching is needed, it will be done below. Before running the *
162* match we must set up a match_data block for holding the result. Using *
163* pcre2_match_data_create_from_pattern() ensures that the block is *
164* exactly the right size for the number of capturing parentheses in the *
165* pattern. If you need to know the actual size of a match_data block as *
166* a number of bytes, you can find it like this: *
167* *
168* PCRE2_SIZE match_data_size = pcre2_get_match_data_size(match_data); *
169*************************************************************************/
170match_data = pcre2_match_data_create_from_pattern(re, NULL);
172/* Now run the match. */
174rc = pcre2_match(
176 re, /* the compiled pattern */
177 subject, /* the subject string */
178 subject_length, /* the length of the subject */
179 0, /* start at offset 0 in the subject */
180 0, /* default options */
181 match_data, /* block for storing the result */
182 NULL); /* use default match context */
183/* Matching failed: handle error cases */
185if (rc < 0)
187 {
188 switch(rc)
189 {
190 case PCRE2_ERROR_NOMATCH: printf("No match\n"); break;
191 /*
192 Handle other special cases if you like
193 */
194 default: printf("Matching error %d\n", rc); break;
195 }
196 pcre2_match_data_free(match_data); /* Release memory used for the match */
197 pcre2_code_free(re); /* data and the compiled pattern. */
198 return 1;
199 }
200/* Match succeeded. Get a pointer to the output vector, where string offsets
202are stored. */
203ovector = pcre2_get_ovector_pointer(match_data);
205printf("Match succeeded at offset %d\n", (int)ovector[0]);
206/*************************************************************************
209* We have found the first match within the subject string. If the output *
210* vector wasn’t big enough, say so. Then output any substrings that were *
211* captured. *
212*************************************************************************/
213/* The output vector wasn’t big enough. This should not happen, because we used
215pcre2_match_data_create_from_pattern() above. */
216if (rc == 0)
218 printf("ovector was not big enough for all the captured substrings\n");
219/* Since release 10.38 PCRE2 has locked out the use of \K in lookaround
221assertions. However, there is an option to re‐enable the old behaviour. If that
222is set, it is possible to run patterns such as /(?=.\K)/ that use \K in an
223assertion to set the start of a match later than its end. In this demonstration
224program, we show how to detect this case, but it shouldn’t arise because the
225option is never set. */
226if (ovector[0] > ovector[1])
228 {
229 printf("\\K was used in an assertion to set the match start after its end.\n"
230 "From end to start the match was: %.*s\n", (int)(ovector[0] ‐ ovector[1]),
231 (char *)(subject + ovector[1]));
232 printf("Run abandoned\n");
233 pcre2_match_data_free(match_data);
234 pcre2_code_free(re);
235 return 1;
236 }
237/* Show substrings stored in the output vector by number. Obviously, in a real
239application you might want to do things other than print them. */
240for (i = 0; i < rc; i++)
242 {
243 PCRE2_SPTR substring_start = subject + ovector[2*i];
244 PCRE2_SIZE substring_length = ovector[2*i+1] ‐ ovector[2*i];
245 printf("%2d: %.*s\n", i, (int)substring_length, (char *)substring_start);
246 }
247/**************************************************************************
250* That concludes the basic part of this demonstration program. We have *
251* compiled a pattern, and performed a single match. The code that follows *
252* shows first how to access named substrings, and then how to code for *
253* repeated matches on the same subject. *
254**************************************************************************/
255/* See if there are any named substrings, and if so, show them by name. First
257we have to extract the count of named parentheses from the pattern. */
258(void)pcre2_pattern_info(
260 re, /* the compiled pattern */
261 PCRE2_INFO_NAMECOUNT, /* get the number of named substrings */
262 &namecount); /* where to put the answer */
263if (namecount == 0) printf("No named substrings\n"); else
265 {
266 PCRE2_SPTR tabptr;
267 printf("Named substrings\n");
268 /* Before we can access the substrings, we must extract the table for
270 translating names to numbers, and the size of each entry in the table. */
271 (void)pcre2_pattern_info(
273 re, /* the compiled pattern */
274 PCRE2_INFO_NAMETABLE, /* address of the table */
275 &name_table); /* where to put the answer */
276 (void)pcre2_pattern_info(
278 re, /* the compiled pattern */
279 PCRE2_INFO_NAMEENTRYSIZE, /* size of each entry in the table */
280 &name_entry_size); /* where to put the answer */
281 /* Now we can scan the table and, for each entry, print the number, the name,
283 and the substring itself. In the 8‐bit library the number is held in two
284 bytes, most significant first. */
285 tabptr = name_table;
287 for (i = 0; i < namecount; i++)
288 {
289 int n = (tabptr[0] << 8) | tabptr[1];
290 printf("(%d) %*s: %.*s\n", n, name_entry_size ‐ 3, tabptr + 2,
291 (int)(ovector[2*n+1] ‐ ovector[2*n]), subject + ovector[2*n]);
292 tabptr += name_entry_size;
293 }
294 }
295/*************************************************************************
298* If the "‐g" option was given on the command line, we want to continue *
299* to search for additional matches in the subject string, in a similar *
300* way to the /g option in Perl. This turns out to be trickier than you *
301* might think because of the possibility of matching an empty string. *
302* What happens is as follows: *
303* *
304* If the previous match was NOT for an empty string, we can just start *
305* the next match at the end of the previous one. *
306* *
307* If the previous match WAS for an empty string, we can’t do that, as it *
308* would lead to an infinite loop. Instead, a call of pcre2_match() is *
309* made with the PCRE2_NOTEMPTY_ATSTART and PCRE2_ANCHORED flags set. The *
310* first of these tells PCRE2 that an empty string at the start of the *
311* subject is not a valid match; other possibilities must be tried. The *
312* second flag restricts PCRE2 to one match attempt at the initial string *
313* position. If this match succeeds, an alternative to the empty string *
314* match has been found, and we can print it and proceed round the loop, *
315* advancing by the length of whatever was found. If this match does not *
316* succeed, we still stay in the loop, advancing by just one character. *
317* In UTF‐8 mode, which can be set by (*UTF) in the pattern, this may be *
318* more than one byte. *
319* *
320* However, there is a complication concerned with newlines. When the *
321* newline convention is such that CRLF is a valid newline, we must *
322* advance by two characters rather than one. The newline convention can *
323* be set in the regex by (*CR), etc.; if not, we must find the default. *
324*************************************************************************/
325if (!find_all) /* Check for ‐g */
327 {
328 pcre2_match_data_free(match_data); /* Release the memory that was used */
329 pcre2_code_free(re); /* for the match data and the pattern. */
330 return 0; /* Exit the program. */
331 }
332/* Before running the loop, check for UTF‐8 and whether CRLF is a valid newline
334sequence. First, find the options with which the regex was compiled and extract
335the UTF state. */
336(void)pcre2_pattern_info(re, PCRE2_INFO_ALLOPTIONS, &option_bits);
338utf8 = (option_bits & PCRE2_UTF) != 0;
339/* Now find the newline convention and see whether CRLF is a valid newline
341sequence. */
342(void)pcre2_pattern_info(re, PCRE2_INFO_NEWLINE, &newline);
344crlf_is_newline = newline == PCRE2_NEWLINE_ANY ||
345 newline == PCRE2_NEWLINE_CRLF ||
346 newline == PCRE2_NEWLINE_ANYCRLF;
347/* Loop for second and subsequent matches */
349for (;;)
351 {
352 uint32_t options = 0; /* Normally no options */
353 PCRE2_SIZE start_offset = ovector[1]; /* Start at end of previous match */
354 /* If the previous match was for an empty string, we are finished if we are
356 at the end of the subject. Otherwise, arrange to run another match at the
357 same point to see if a non‐empty match can be found. */
358 if (ovector[0] == ovector[1])
360 {
361 if (ovector[0] == subject_length) break;
362 options = PCRE2_NOTEMPTY_ATSTART | PCRE2_ANCHORED;
363 }
364 /* If the previous match was not an empty string, there is one tricky case to
366 consider. If a pattern contains \K within a lookbehind assertion at the
367 start, the end of the matched string can be at the offset where the match
368 started. Without special action, this leads to a loop that keeps on matching
369 the same substring. We must detect this case and arrange to move the start on
370 by one character. The pcre2_get_startchar() function returns the starting
371 offset that was passed to pcre2_match(). */
372 else
374 {
375 PCRE2_SIZE startchar = pcre2_get_startchar(match_data);
376 if (start_offset <= startchar)
377 {
378 if (startchar >= subject_length) break; /* Reached end of subject. */
379 start_offset = startchar + 1; /* Advance by one character. */
380 if (utf8) /* If UTF‐8, it may be more */
381 { /* than one code unit. */
382 for (; start_offset < subject_length; start_offset++)
383 if ((subject[start_offset] & 0xc0) != 0x80) break;
384 }
385 }
386 }
387 /* Run the next matching operation */
389 rc = pcre2_match(
391 re, /* the compiled pattern */
392 subject, /* the subject string */
393 subject_length, /* the length of the subject */
394 start_offset, /* starting offset in the subject */
395 options, /* options */
396 match_data, /* block for storing the result */
397 NULL); /* use default match context */
398 /* This time, a result of NOMATCH isn’t an error. If the value in "options"
400 is zero, it just means we have found all possible matches, so the loop ends.
401 Otherwise, it means we have failed to find a non‐empty‐string match at a
402 point where there was a previous empty‐string match. In this case, we do what
403 Perl does: advance the matching position by one character, and continue. We
404 do this by setting the "end of previous match" offset, because that is picked
405 up at the top of the loop as the point at which to start again.
406 There are two complications: (a) When CRLF is a valid newline sequence, and
408 the current position is just before it, advance by an extra byte. (b)
409 Otherwise we must ensure that we skip an entire UTF character if we are in
410 UTF mode. */
411 if (rc == PCRE2_ERROR_NOMATCH)
413 {
414 if (options == 0) break; /* All matches found */
415 ovector[1] = start_offset + 1; /* Advance one code unit */
416 if (crlf_is_newline && /* If CRLF is a newline & */
417 start_offset < subject_length ‐ 1 && /* we are at CRLF, */
418 subject[start_offset] == ’\r’ &&
419 subject[start_offset + 1] == ’\n’)
420 ovector[1] += 1; /* Advance by one more. */
421 else if (utf8) /* Otherwise, ensure we */
422 { /* advance a whole UTF‐8 */
423 while (ovector[1] < subject_length) /* character. */
424 {
425 if ((subject[ovector[1]] & 0xc0) != 0x80) break;
426 ovector[1] += 1;
427 }
428 }
429 continue; /* Go round the loop again */
430 }
431 /* Other matching errors are not recoverable. */
433 if (rc < 0)
435 {
436 printf("Matching error %d\n", rc);
437 pcre2_match_data_free(match_data);
438 pcre2_code_free(re);
439 return 1;
440 }
441 /* Match succeeded */
443 printf("\nMatch succeeded again at offset %d\n", (int)ovector[0]);
445 /* The match succeeded, but the output vector wasn’t big enough. This
447 should not happen. */
448 if (rc == 0)
450 printf("ovector was not big enough for all the captured substrings\n");
451 /* We must guard against patterns such as /(?=.\K)/ that use \K in an
453 assertion to set the start of a match later than its end. In this
454 demonstration program, we just detect this case and give up. */
455 if (ovector[0] > ovector[1])
457 {
458 printf("\\K was used in an assertion to set the match start after its end.\n"
459 "From end to start the match was: %.*s\n", (int)(ovector[0] ‐ ovector[1]),
460 (char *)(subject + ovector[1]));
461 printf("Run abandoned\n");
462 pcre2_match_data_free(match_data);
463 pcre2_code_free(re);
464 return 1;
465 }
466 /* As before, show substrings stored in the output vector by number, and then
468 also any named substrings. */
469 for (i = 0; i < rc; i++)
471 {
472 PCRE2_SPTR substring_start = subject + ovector[2*i];
473 size_t substring_length = ovector[2*i+1] ‐ ovector[2*i];
474 printf("%2d: %.*s\n", i, (int)substring_length, (char *)substring_start);
475 }
476 if (namecount == 0) printf("No named substrings\n"); else
478 {
479 PCRE2_SPTR tabptr = name_table;
480 printf("Named substrings\n");
481 for (i = 0; i < namecount; i++)
482 {
483 int n = (tabptr[0] << 8) | tabptr[1];
484 printf("(%d) %*s: %.*s\n", n, name_entry_size ‐ 3, tabptr + 2,
485 (int)(ovector[2*n+1] ‐ ovector[2*n]), subject + ovector[2*n]);
486 tabptr += name_entry_size;
487 }
488 }
489 } /* End of loop to find second and subsequent matches */
490printf("\n");
492pcre2_match_data_free(match_data);
493pcre2_code_free(re);
494return 0;
495}
496/* End of pcre2demo.c */
498