code/trunk/pcredemo.c

/*************************************************
*           PCRE DEMONSTRATION PROGRAM           *
*************************************************/

/* This is a demonstration program to illustrate the most straightforward ways
of calling the PCRE regular expression library from a C program. See the
pcresample documentation for a short discussion.

Compile thuswise:
  gcc -Wall pcredemo.c -I/usr/local/include -L/usr/local/lib \
    -R/usr/local/lib -lpcre

Replace "/usr/local/include" and "/usr/local/lib" with wherever the include and
library files for PCRE are installed on your system. You don't need -I and -L 
if PCRE is installed in the standard system libraries. Only some operating
systems (e.g. Solaris) use the -R option.
*/


#include <stdio.h>
#include <string.h>
#include <pcre.h>

#define OVECCOUNT 30    /* should be a multiple of 3 */


int main(int argc, char **argv)
{
pcre *re;
const char *error;
char *pattern;
char *subject;
unsigned char *name_table;
int erroffset;
int find_all;
int namecount;
int name_entry_size;
int ovector[OVECCOUNT];
int subject_length;
int rc, i;


/**************************************************************************
* First, sort out the command line. There is only one possible option at  *
* the moment, "-g" to request repeated matching to find all occurrences,  *
* like Perl's /g option. We set the variable find_all to a non-zero value *
* if the -g option is present. Apart from that, there must be exactly two *
* arguments.                                                              *
**************************************************************************/

find_all = 0;
for (i = 1; i < argc; i++)
  {
  if (strcmp(argv[i], "-g") == 0) find_all = 1;
    else break;
  }

/* After the options, we require exactly two arguments, which are the pattern,
and the subject string. */

if (argc - i != 2)
  {
  printf("Two arguments required: a regex and a subject string\n");
  return 1;
  }

pattern = argv[i];
subject = argv[i+1];
subject_length = (int)strlen(subject);


/*************************************************************************
* Now we are going to compile the regular expression pattern, and handle *
* and errors that are detected.                                          *
*************************************************************************/

re = pcre_compile(
  pattern,              /* the pattern */
  0,                    /* default options */
  &error,               /* for error message */
  &erroffset,           /* for error offset */
  NULL);                /* use default character tables */

/* Compilation failed: print the error message and exit */

if (re == NULL)
  {
  printf("PCRE compilation failed at offset %d: %s\n", erroffset, error);
  return 1;
  }


/*************************************************************************
* If the compilation succeeded, we call PCRE again, in order to do a     *
* pattern match against the subject string. This does just ONE match. If *
* further matching is needed, it will be done below.                     *
*************************************************************************/

rc = pcre_exec(
  re,                   /* the compiled pattern */
  NULL,                 /* no extra data - we didn't study the pattern */
  subject,              /* the subject string */
  subject_length,       /* the length of the subject */
  0,                    /* start at offset 0 in the subject */
  0,                    /* default options */
  ovector,              /* output vector for substring information */
  OVECCOUNT);           /* number of elements in the output vector */

/* Matching failed: handle error cases */

if (rc < 0)
  {
  switch(rc)
    {
    case PCRE_ERROR_NOMATCH: printf("No match\n"); break;
    /*
    Handle other special cases if you like
    */
    default: printf("Matching error %d\n", rc); break;
    }
  pcre_free(re);     /* Release memory used for the compiled pattern */
  return 1;
  }

/* Match succeded */

printf("\nMatch succeeded at offset %d\n", ovector[0]);


/*************************************************************************
* We have found the first match within the subject string. If the output *
* vector wasn't big enough, set its size to the maximum. Then output any *
* substrings that were captured.                                         *
*************************************************************************/

/* The output vector wasn't big enough */

if (rc == 0)
  {
  rc = OVECCOUNT/3;
  printf("ovector only has room for %d captured substrings\n", rc - 1);
  }

/* Show substrings stored in the output vector by number. Obviously, in a real
application you might want to do things other than print them. */

for (i = 0; i < rc; i++)
  {
  char *substring_start = subject + ovector[2*i];
  int substring_length = ovector[2*i+1] - ovector[2*i];
  printf("%2d: %.*s\n", i, substring_length, substring_start);
  }


/**************************************************************************
* That concludes the basic part of this demonstration program. We have    *
* compiled a pattern, and performed a single match. The code that follows *
* first shows how to access named substrings, and then how to code for    *
* repeated matches on the same subject.                                   *
**************************************************************************/

/* See if there are any named substrings, and if so, show them by name. First
we have to extract the count of named parentheses from the pattern. */

(void)pcre_fullinfo(
  re,                   /* the compiled pattern */
  NULL,                 /* no extra data - we didn't study the pattern */
  PCRE_INFO_NAMECOUNT,  /* number of named substrings */
  &namecount);          /* where to put the answer */

if (namecount <= 0) printf("No named substrings\n"); else
  {
  unsigned char *tabptr;
  printf("Named substrings\n");

  /* Before we can access the substrings, we must extract the table for
  translating names to numbers, and the size of each entry in the table. */

  (void)pcre_fullinfo(
    re,                       /* the compiled pattern */
    NULL,                     /* no extra data - we didn't study the pattern */
    PCRE_INFO_NAMETABLE,      /* address of the table */
    &name_table);             /* where to put the answer */

  (void)pcre_fullinfo(
    re,                       /* the compiled pattern */
    NULL,                     /* no extra data - we didn't study the pattern */
    PCRE_INFO_NAMEENTRYSIZE,  /* size of each entry in the table */
    &name_entry_size);        /* where to put the answer */

  /* Now we can scan the table and, for each entry, print the number, the name,
  and the substring itself. */

  tabptr = name_table;
  for (i = 0; i < namecount; i++)
    {
    int n = (tabptr[0] << 8) | tabptr[1];
    printf("(%d) %*s: %.*s\n", n, name_entry_size - 3, tabptr + 2,
      ovector[2*n+1] - ovector[2*n], subject + ovector[2*n]);
    tabptr += name_entry_size;
    }
  }


/*************************************************************************
* If the "-g" option was given on the command line, we want to continue  *
* to search for additional matches in the subject string, in a similar   *
* way to the /g option in Perl. This turns out to be trickier than you   *
* might think because of the possibility of matching an empty string.    *
* What happens is as follows:                                            *
*                                                                        *
* If the previous match was NOT for an empty string, we can just start   *
* the next match at the end of the previous one.                         *
*                                                                        *
* If the previous match WAS for an empty string, we can't do that, as it *
* would lead to an infinite loop. Instead, a special call of pcre_exec() *
* is made with the PCRE_NOTEMPTY and PCRE_ANCHORED flags set. The first  *
* of these tells PCRE that an empty string is not a valid match; other   *
* possibilities must be tried. The second flag restricts PCRE to one     *
* match attempt at the initial string position. If this match succeeds,  *
* an alternative to the empty string match has been found, and we can    *
* proceed round the loop.                                                *
*************************************************************************/

if (!find_all)
  {
  pcre_free(re);   /* Release the memory used for the compiled pattern */
  return 0;        /* Finish unless -g was given */
  }

/* Loop for second and subsequent matches */

for (;;)
  {
  int options = 0;                 /* Normally no options */
  int start_offset = ovector[1];   /* Start at end of previous match */

  /* If the previous match was for an empty string, we are finished if we are
  at the end of the subject. Otherwise, arrange to run another match at the
  same point to see if a non-empty match can be found. */

  if (ovector[0] == ovector[1])
    {
    if (ovector[0] == subject_length) break;
    options = PCRE_NOTEMPTY | PCRE_ANCHORED;
    }

  /* Run the next matching operation */

  rc = pcre_exec(
    re,                   /* the compiled pattern */
    NULL,                 /* no extra data - we didn't study the pattern */
    subject,              /* the subject string */
    subject_length,       /* the length of the subject */
    start_offset,         /* starting offset in the subject */
    options,              /* options */
    ovector,              /* output vector for substring information */
    OVECCOUNT);           /* number of elements in the output vector */

  /* This time, a result of NOMATCH isn't an error. If the value in "options"
  is zero, it just means we have found all possible matches, so the loop ends.
  Otherwise, it means we have failed to find a non-empty-string match at a
  point where there was a previous empty-string match. In this case, we do what
  Perl does: advance the matching position by one, and continue. We do this by
  setting the "end of previous match" offset, because that is picked up at the
  top of the loop as the point at which to start again. */

  if (rc == PCRE_ERROR_NOMATCH)
    {
    if (options == 0) break;
    ovector[1] = start_offset + 1;
    continue;    /* Go round the loop again */
    }

  /* Other matching errors are not recoverable. */

  if (rc < 0)
    {
    printf("Matching error %d\n", rc);
    pcre_free(re);    /* Release memory used for the compiled pattern */
    return 1;
    }

  /* Match succeded */

  printf("\nMatch succeeded again at offset %d\n", ovector[0]);

  /* The match succeeded, but the output vector wasn't big enough. */

  if (rc == 0)
    {
    rc = OVECCOUNT/3;
    printf("ovector only has room for %d captured substrings\n", rc - 1);
    }

  /* As before, show substrings stored in the output vector by number, and then
  also any named substrings. */

  for (i = 0; i < rc; i++)
    {
    char *substring_start = subject + ovector[2*i];
    int substring_length = ovector[2*i+1] - ovector[2*i];
    printf("%2d: %.*s\n", i, substring_length, substring_start);
    }

  if (namecount <= 0) printf("No named substrings\n"); else
    {
    unsigned char *tabptr = name_table;
    printf("Named substrings\n");
    for (i = 0; i < namecount; i++)
      {
      int n = (tabptr[0] << 8) | tabptr[1];
      printf("(%d) %*s: %.*s\n", n, name_entry_size - 3, tabptr + 2,
        ovector[2*n+1] - ovector[2*n], subject + ovector[2*n]);
      tabptr += name_entry_size;
      }
    }
  }      /* End of loop to find second and subsequent matches */

printf("\n");
pcre_free(re);       /* Release memory used for the compiled pattern */
return 0;
}

/* End of pcredemo.c */
1	/*************************************************
2	* PCRE DEMONSTRATION PROGRAM *
3	*************************************************/
4
5	/* This is a demonstration program to illustrate the most straightforward ways
6	of calling the PCRE regular expression library from a C program. See the
7	pcresample documentation for a short discussion.
8
9	Compile thuswise:
10	gcc -Wall pcredemo.c -I/usr/local/include -L/usr/local/lib \
11	-R/usr/local/lib -lpcre
12
13	Replace "/usr/local/include" and "/usr/local/lib" with wherever the include and
14	library files for PCRE are installed on your system. You don't need -I and -L
15	if PCRE is installed in the standard system libraries. Only some operating
16	systems (e.g. Solaris) use the -R option.
17	*/
18
19
20	#include <stdio.h>
21	#include <string.h>
22	#include <pcre.h>
23
24	#define OVECCOUNT 30 /* should be a multiple of 3 */
25
26
27	int main(int argc, char **argv)
28	{
29	pcre *re;
30	const char *error;
31	char *pattern;
32	char *subject;
33	unsigned char *name_table;
34	int erroffset;
35	int find_all;
36	int namecount;
37	int name_entry_size;
38	int ovector[OVECCOUNT];
39	int subject_length;
40	int rc, i;
41
42
43	/**************************************************************************
44	* First, sort out the command line. There is only one possible option at *
45	* the moment, "-g" to request repeated matching to find all occurrences, *
46	* like Perl's /g option. We set the variable find_all to a non-zero value *
47	* if the -g option is present. Apart from that, there must be exactly two *
48	* arguments. *
49	**************************************************************************/
50
51	find_all = 0;
52	for (i = 1; i < argc; i++)
53	{
54	if (strcmp(argv[i], "-g") == 0) find_all = 1;
55	else break;
56	}
57
58	/* After the options, we require exactly two arguments, which are the pattern,
59	and the subject string. */
60
61	if (argc - i != 2)
62	{
63	printf("Two arguments required: a regex and a subject string\n");
64	return 1;
65	}
66
67	pattern = argv[i];
68	subject = argv[i+1];
69	subject_length = (int)strlen(subject);
70
71
72	/*************************************************************************
73	* Now we are going to compile the regular expression pattern, and handle *
74	* and errors that are detected. *
75	*************************************************************************/
76
77	re = pcre_compile(
78	pattern, /* the pattern */
79	0, /* default options */
80	&error, /* for error message */
81	&erroffset, /* for error offset */
82	NULL); /* use default character tables */
83
84	/* Compilation failed: print the error message and exit */
85
86	if (re == NULL)
87	{
88	printf("PCRE compilation failed at offset %d: %s\n", erroffset, error);
89	return 1;
90	}
91
92
93	/*************************************************************************
94	* If the compilation succeeded, we call PCRE again, in order to do a *
95	* pattern match against the subject string. This does just ONE match. If *
96	* further matching is needed, it will be done below. *
97	*************************************************************************/
98
99	rc = pcre_exec(
100	re, /* the compiled pattern */
101	NULL, /* no extra data - we didn't study the pattern */
102	subject, /* the subject string */
103	subject_length, /* the length of the subject */
104	0, /* start at offset 0 in the subject */
105	0, /* default options */
106	ovector, /* output vector for substring information */
107	OVECCOUNT); /* number of elements in the output vector */
108
109	/* Matching failed: handle error cases */
110
111	if (rc < 0)
112	{
113	switch(rc)
114	{
115	case PCRE_ERROR_NOMATCH: printf("No match\n"); break;
116	/*
117	Handle other special cases if you like
118	*/
119	default: printf("Matching error %d\n", rc); break;
120	}
121	pcre_free(re); /* Release memory used for the compiled pattern */
122	return 1;
123	}
124
125	/* Match succeded */
126
127	printf("\nMatch succeeded at offset %d\n", ovector[0]);
128
129
130	/*************************************************************************
131	* We have found the first match within the subject string. If the output *
132	* vector wasn't big enough, set its size to the maximum. Then output any *
133	* substrings that were captured. *
134	*************************************************************************/
135
136	/* The output vector wasn't big enough */
137
138	if (rc == 0)
139	{
140	rc = OVECCOUNT/3;
141	printf("ovector only has room for %d captured substrings\n", rc - 1);
142	}
143
144	/* Show substrings stored in the output vector by number. Obviously, in a real
145	application you might want to do things other than print them. */
146
147	for (i = 0; i < rc; i++)
148	{
149	char substring_start = subject + ovector[2i];
150	int substring_length = ovector[2i+1] - ovector[2i];
151	printf("%2d: %.*s\n", i, substring_length, substring_start);
152	}
153
154
155	/**************************************************************************
156	* That concludes the basic part of this demonstration program. We have *
157	* compiled a pattern, and performed a single match. The code that follows *
158	* first shows how to access named substrings, and then how to code for *
159	* repeated matches on the same subject. *
160	**************************************************************************/
161
162	/* See if there are any named substrings, and if so, show them by name. First
163	we have to extract the count of named parentheses from the pattern. */
164
165	(void)pcre_fullinfo(
166	re, /* the compiled pattern */
167	NULL, /* no extra data - we didn't study the pattern */
168	PCRE_INFO_NAMECOUNT, /* number of named substrings */
169	&namecount); /* where to put the answer */
170
171	if (namecount <= 0) printf("No named substrings\n"); else
172	{
173	unsigned char *tabptr;
174	printf("Named substrings\n");
175
176	/* Before we can access the substrings, we must extract the table for
177	translating names to numbers, and the size of each entry in the table. */
178
179	(void)pcre_fullinfo(
180	re, /* the compiled pattern */
181	NULL, /* no extra data - we didn't study the pattern */
182	PCRE_INFO_NAMETABLE, /* address of the table */
183	&name_table); /* where to put the answer */
184
185	(void)pcre_fullinfo(
186	re, /* the compiled pattern */
187	NULL, /* no extra data - we didn't study the pattern */
188	PCRE_INFO_NAMEENTRYSIZE, /* size of each entry in the table */
189	&name_entry_size); /* where to put the answer */
190
191	/* Now we can scan the table and, for each entry, print the number, the name,
192	and the substring itself. */
193
194	tabptr = name_table;
195	for (i = 0; i < namecount; i++)
196	{
197	int n = (tabptr[0] << 8) \| tabptr[1];
198	printf("(%d) %s: %.s\n", n, name_entry_size - 3, tabptr + 2,
199	ovector[2n+1] - ovector[2n], subject + ovector[2*n]);
200	tabptr += name_entry_size;
201	}
202	}
203
204
205	/*************************************************************************
206	* If the "-g" option was given on the command line, we want to continue *
207	* to search for additional matches in the subject string, in a similar *
208	* way to the /g option in Perl. This turns out to be trickier than you *
209	* might think because of the possibility of matching an empty string. *
210	* What happens is as follows: *
211	* *
212	* If the previous match was NOT for an empty string, we can just start *
213	* the next match at the end of the previous one. *
214	* *
215	* If the previous match WAS for an empty string, we can't do that, as it *
216	* would lead to an infinite loop. Instead, a special call of pcre_exec() *
217	* is made with the PCRE_NOTEMPTY and PCRE_ANCHORED flags set. The first *
218	* of these tells PCRE that an empty string is not a valid match; other *
219	* possibilities must be tried. The second flag restricts PCRE to one *
220	* match attempt at the initial string position. If this match succeeds, *
221	* an alternative to the empty string match has been found, and we can *
222	* proceed round the loop. *
223	*************************************************************************/
224
225	if (!find_all)
226	{
227	pcre_free(re); /* Release the memory used for the compiled pattern */
228	return 0; /* Finish unless -g was given */
229	}
230
231	/* Loop for second and subsequent matches */
232
233	for (;;)
234	{
235	int options = 0; /* Normally no options */
236	int start_offset = ovector[1]; /* Start at end of previous match */
237
238	/* If the previous match was for an empty string, we are finished if we are
239	at the end of the subject. Otherwise, arrange to run another match at the
240	same point to see if a non-empty match can be found. */
241
242	if (ovector[0] == ovector[1])
243	{
244	if (ovector[0] == subject_length) break;
245	options = PCRE_NOTEMPTY \| PCRE_ANCHORED;
246	}
247
248	/* Run the next matching operation */
249
250	rc = pcre_exec(
251	re, /* the compiled pattern */
252	NULL, /* no extra data - we didn't study the pattern */
253	subject, /* the subject string */
254	subject_length, /* the length of the subject */
255	start_offset, /* starting offset in the subject */
256	options, /* options */
257	ovector, /* output vector for substring information */
258	OVECCOUNT); /* number of elements in the output vector */
259
260	/* This time, a result of NOMATCH isn't an error. If the value in "options"
261	is zero, it just means we have found all possible matches, so the loop ends.
262	Otherwise, it means we have failed to find a non-empty-string match at a
263	point where there was a previous empty-string match. In this case, we do what
264	Perl does: advance the matching position by one, and continue. We do this by
265	setting the "end of previous match" offset, because that is picked up at the
266	top of the loop as the point at which to start again. */
267
268	if (rc == PCRE_ERROR_NOMATCH)
269	{
270	if (options == 0) break;
271	ovector[1] = start_offset + 1;
272	continue; /* Go round the loop again */
273	}
274
275	/* Other matching errors are not recoverable. */
276
277	if (rc < 0)
278	{
279	printf("Matching error %d\n", rc);
280	pcre_free(re); /* Release memory used for the compiled pattern */
281	return 1;
282	}
283
284	/* Match succeded */
285
286	printf("\nMatch succeeded again at offset %d\n", ovector[0]);
287
288	/* The match succeeded, but the output vector wasn't big enough. */
289
290	if (rc == 0)
291	{
292	rc = OVECCOUNT/3;
293	printf("ovector only has room for %d captured substrings\n", rc - 1);
294	}
295
296	/* As before, show substrings stored in the output vector by number, and then
297	also any named substrings. */
298
299	for (i = 0; i < rc; i++)
300	{
301	char substring_start = subject + ovector[2i];
302	int substring_length = ovector[2i+1] - ovector[2i];
303	printf("%2d: %.*s\n", i, substring_length, substring_start);
304	}
305
306	if (namecount <= 0) printf("No named substrings\n"); else
307	{
308	unsigned char *tabptr = name_table;
309	printf("Named substrings\n");
310	for (i = 0; i < namecount; i++)
311	{
312	int n = (tabptr[0] << 8) \| tabptr[1];
313	printf("(%d) %s: %.s\n", n, name_entry_size - 3, tabptr + 2,
314	ovector[2n+1] - ovector[2n], subject + ovector[2*n]);
315	tabptr += name_entry_size;
316	}
317	}
318	} /* End of loop to find second and subsequent matches */
319
320	printf("\n");
321	pcre_free(re); /* Release memory used for the compiled pattern */
322	return 0;
323	}
324
325	/* End of pcredemo.c */
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