/*************************************************
* 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 ("man
pcresample" if you have
the PCRE man pages installed).
In Unix-like environments, if
PCRE is installed in your standard system
libraries, you should be able to compile this program using
this command:
gcc -Wall pcredemo.c -lpcre -o pcredemo
If PCRE is not installed in a
standard place, it is likely to be installed with
support for the pkg-config mechanism. If you have
pkg-config, you can compile
this program using this command:
gcc -Wall pcredemo.c ‘pkg-config --cflags --libs libpcre‘ -o pcredemo
If you do not have pkg-config, you may have to use this:
gcc -Wall pcredemo.c
-I/usr/local/include -L/usr/local/lib \
-R/usr/local/lib -lpcre -o pcredemo
Replace
"/usr/local/include" and
"/usr/local/lib" with wherever the include and
library files for PCRE are installed on your system. Only
some operating
systems (e.g. Solaris) use the -R option.
Building under Windows:
If you want to statically link
this program against a non-dll .a file, you must
define PCRE_STATIC before including pcre.h, otherwise the
pcre_malloc() and
pcre_free() exported functions will be declared
__declspec(dllimport), with
unwanted results. So in this environment, uncomment the
following line. */
/* #define PCRE_STATIC */
#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;
unsigned int option_bits;
int erroffset;
int find_all;
int crlf_is_newline;
int namecount;
int name_entry_size;
int ovector[OVECCOUNT];
int subject_length;
int rc, i;
int utf8;
/**************************************************************************
* 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 succeeded */
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, say so. 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 *
* shows first 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_ATSTART and PCRE_ANCHORED
flags set. *
* The first of these tells PCRE that an empty string at the
start of the *
* subject 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 print it and proceed
round the loop, *
* advancing by the length of whatever was found. If this
match does not *
* succeed, we still stay in the loop, advancing by just one
character. *
* In UTF-8 mode, which can be set by (*UTF8) in the pattern,
this may be *
* more than one byte. *
* *
* However, there is a complication concerned with newlines.
When the *
* newline convention is such that CRLF is a valid newline,
we must *
* advance by two characters rather than one. The newline
convention can *
* be set in the regex by (*CR), etc.; if not, we must find
the default. *
*************************************************************************/
if (!find_all) /* Check for -g
*/
{
pcre_free(re); /* Release the memory used for the compiled
pattern */
return 0; /* Finish unless -g was given */
}
/* Before running the loop,
check for UTF-8 and whether CRLF is a valid newline
sequence. First, find the options with which the regex was
compiled; extract
the UTF-8 state, and mask off all but the newline options.
*/
(void)pcre_fullinfo(re, NULL,
PCRE_INFO_OPTIONS, &option_bits);
utf8 = option_bits & PCRE_UTF8;
option_bits &=
PCRE_NEWLINE_CR|PCRE_NEWLINE_LF|PCRE_NEWLINE_CRLF|
PCRE_NEWLINE_ANY|PCRE_NEWLINE_ANYCRLF;
/* If no newline options were
set, find the default newline convention from the
build configuration. */
if (option_bits == 0)
{
int d;
(void)pcre_config(PCRE_CONFIG_NEWLINE, &d);
/* Note that these values are always the ASCII ones, even in
EBCDIC environments. CR = 13, NL = 10. */
option_bits = (d == 13)? PCRE_NEWLINE_CR :
(d == 10)? PCRE_NEWLINE_LF :
(d == (13<<8 | 10))? PCRE_NEWLINE_CRLF :
(d == -2)? PCRE_NEWLINE_ANYCRLF :
(d == -1)? PCRE_NEWLINE_ANY : 0;
}
/* See if CRLF is a valid newline sequence. */
crlf_is_newline =
option_bits == PCRE_NEWLINE_ANY ||
option_bits == PCRE_NEWLINE_CRLF ||
option_bits == PCRE_NEWLINE_ANYCRLF;
/* 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_ATSTART | 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 character,
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.
There are two complications: (a)
When CRLF is a valid newline sequence, and
the current position is just before it, advance by an extra
byte. (b)
Otherwise we must ensure that we skip an entire UTF-8
character if we are in
UTF-8 mode. */
if (rc == PCRE_ERROR_NOMATCH)
{
if (options == 0) break; /* All matches found */
ovector[1] = start_offset + 1; /* Advance one byte */
if (crlf_is_newline && /* If CRLF is newline &
*/
start_offset < subject_length - 1 && /* we are at
CRLF, */
subject[start_offset] == ’\r’ &&
subject[start_offset + 1] == ’\n’)
ovector[1] += 1; /* Advance by one more. */
else if (utf8) /* Otherwise, ensure we */
{ /* advance a whole UTF-8 */
while (ovector[1] < subject_length) /* character. */
{
if ((subject[ovector[1]] & 0xc0) != 0x80) break;
ovector[1] += 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 succeeded */
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 */