/*************************************************
*           PCRE2 DEMONSTRATION PROGRAM          *
*************************************************/
/* This is a demonstration program to illustrate a straightforward way of
using the PCRE2 regular expression library from a C program. See the
pcre2sample documentation for a short discussion ("man pcre2sample" if you have
the PCRE2 man pages installed). PCRE2 is a revised API for the library, and is
incompatible with the original PCRE API.
There are actually three libraries, each supporting a different code unit
width. This demonstration program uses the 8-bit library. The default is to
process each code unit as a separate character, but if the pattern begins with
"(*UTF)", both it and the subject are treated as UTF-8 strings, where
characters may occupy multiple code units.
In Unix-like environments, if PCRE2 is installed in your standard system
libraries, you should be able to compile this program using this command:
cc -Wall pcre2demo.c -lpcre2-8 -o pcre2demo
If PCRE2 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:
cc -Wall pcre2demo.c `pkg-config --cflags --libs libpcre2-8` -o pcre2demo
If you do not have pkg-config, you may have to use something like this:
cc -Wall pcre2demo.c -I/usr/local/include -L/usr/local/lib \


  -R/usr/local/lib -lpcre2-8 -o pcre2demo
Replace "/usr/local/include" and "/usr/local/lib" with wherever the include and
library files for PCRE2 are installed on your system. Only some operating
systems (Solaris is one) use the -R option.
Building under Windows:
If you want to statically link this program against a non-dll .a file, you must
define PCRE2_STATIC before including pcre2.h, so in this environment, uncomment
the following line. */
/* #define PCRE2_STATIC */
/* The PCRE2_CODE_UNIT_WIDTH macro must be defined before including pcre2.h.
For a program that uses only one code unit width, setting it to 8, 16, or 32
makes it possible to use generic function names such as pcre2_compile(). Note
that just changing 8 to 16 (for example) is not sufficient to convert this
program to process 16-bit characters. Even in a fully 16-bit environment, where
string-handling functions such as strcmp() and printf() work with 16-bit
characters, the code for handling the table of named substrings will still need
to be modified. */
#define PCRE2_CODE_UNIT_WIDTH 8
#include <stdio.h>
#include <string.h>
#include <pcre2.h>
/**************************************************************************
* Here is the program. The API includes the concept of "contexts" for     *
* setting up unusual interface requirements for compiling and matching,   *
* such as custom memory managers and non-standard newline definitions.    *
* This program does not do any of this, so it makes no use of contexts,   *
* always passing NULL where a context could be given.                     *
**************************************************************************/
int main(int argc, char **argv)
{
pcre2_code *re;
PCRE2_SPTR pattern;     /* PCRE2_SPTR is a pointer to unsigned code units of */
PCRE2_SPTR subject;     /* the appropriate width (in this case, 8 bits). */
PCRE2_SPTR name_table;
int errornumber;
int find_all, caseless_match;
int i;
int rc;
uint32_t namecount;
uint32_t name_entry_size;
PCRE2_SIZE erroroffset;
PCRE2_SIZE *ovector;
PCRE2_SIZE ovector_last[2];
PCRE2_SIZE subject_length;
pcre2_match_data *match_data;
/**************************************************************************
* First, sort out the command line. Options:                              *
* - "-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.                                    *
* - "-i" to request caseless matching, like Perl's /i option.  We set the *
*   variable caseless_match to PCRE2_CASELESS if the -i option is         *
*   present.                                                              *
**************************************************************************/
find_all = 0;
caseless_match = 0;
for (i = 1; i < argc; i++)


  {


  if (strcmp(argv[i], "-g") == 0) find_all = 1;


  else if (strcmp(argv[i], "-i") == 0) caseless_match = PCRE2_CASELESS;


  else if (argv[i][0] == '-')


    {


    printf("Unrecognised option %s\n", argv[i]);


    return 1;


    }


  else break;


  }
/* After the options, we require exactly two arguments, which are the pattern,
and the subject string. */
if (argc - i != 2)


  {


  printf("Exactly two arguments required: a regex and a subject string\n");


  return 1;


  }
/* Pattern and subject are char arguments, so they can be straightforwardly
cast to PCRE2_SPTR because we are working in 8-bit code units. The subject
length is cast to PCRE2_SIZE for completeness, though PCRE2_SIZE is in fact
defined to be size_t. */
pattern = (PCRE2_SPTR)argv[i];
subject = (PCRE2_SPTR)argv[i+1];
subject_length = (PCRE2_SIZE)strlen((char *)subject);
/*************************************************************************
* Now we are going to compile the regular expression pattern, and handle *
* any errors that are detected.                                          *
*************************************************************************/
re = pcre2_compile(


  pattern,               /* the pattern */


  PCRE2_ZERO_TERMINATED, /* indicates pattern is zero-terminated */


  caseless_match,        /* possibly enable caseless */


  &errornumber,          /* for error number */


  &erroroffset,          /* for error offset */


  NULL);                 /* use default compile context */
/* Compilation failed: print the error message and exit. */
if (re == NULL)


  {


  PCRE2_UCHAR buffer[256];


  pcre2_get_error_message(errornumber, buffer, sizeof(buffer));


  printf("PCRE2 compilation failed at offset %d: %s\n", (int)erroroffset,


    buffer);


  return 1;


  }
/*************************************************************************
* If the compilation succeeded, we call PCRE2 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. Before running the  *
* match we must set up a match_data block for holding the result. Using  *
* pcre2_match_data_create_from_pattern() ensures that the block is       *
* exactly the right size for the number of capturing parentheses in the  *
* pattern. If you need to know the actual size of a match_data block as  *
* a number of bytes, you can find it like this:                          *
*                                                                        *
* PCRE2_SIZE match_data_size = pcre2_get_match_data_size(match_data);    *
*************************************************************************/
match_data = pcre2_match_data_create_from_pattern(re, NULL);
/* Now run the match. */
rc = pcre2_match(


  re,                   /* the compiled pattern */


  subject,              /* the subject string */


  subject_length,       /* the length of the subject */


  0,                    /* start at offset 0 in the subject */


  0,                    /* default options */


  match_data,           /* block for storing the result */


  NULL);                /* use default match context */
/* Matching failed: handle error cases */
if (rc < 0)


  {


  switch(rc)


    {


    case PCRE2_ERROR_NOMATCH: printf("No match\n"); break;


    /*


    Handle other special cases if you like


    */


    default: printf("Matching error %d\n", rc); break;


    }


  pcre2_match_data_free(match_data);   /* Release memory used for the match */


  pcre2_code_free(re);                 /*   data and the compiled pattern. */


  return 1;


  }
/* Match succeeded. Get a pointer to the output vector, where string offsets
are stored. */
ovector = pcre2_get_ovector_pointer(match_data);
printf("Match succeeded at offset %d\n", (int)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. This should not happen, because we used
pcre2_match_data_create_from_pattern() above. */
if (rc == 0)


  printf("ovector was not big enough for all the captured substrings\n");
/* Since release 10.38 PCRE2 has locked out the use of \K in lookaround
assertions. This is the recommended behaviour. However, the option
PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK allows applications to re-enable the old
behaviour. If that is set, it is possible to run patterns such as /(?=.\K)/ that
use \K in an assertion to set the start of a match later than its end. In this
demonstration program, we show how to detect this case, although it cannot arise
because the option is never set. */
if (ovector[0] > ovector[1])


  {


  printf("\\K was used in an assertion to set the match start after its end.\n"


    "From end to start the match was: %.*s\n", (int)(ovector[0] - ovector[1]),


      (char *)(subject + ovector[1]));


  printf("Run abandoned\n");


  pcre2_match_data_free(match_data);


  pcre2_code_free(re);


  return 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++)


  {


  PCRE2_SPTR substring_start = subject + ovector[2*i];


  PCRE2_SIZE substring_length = ovector[2*i+1] - ovector[2*i];


  printf("%2d: %.*s\n", i, (int)substring_length, (char *)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)pcre2_pattern_info(


  re,                   /* the compiled pattern */


  PCRE2_INFO_NAMECOUNT, /* get the number of named substrings */


  &namecount);          /* where to put the answer */
if (namecount == 0)


  printf("No named substrings\n");
else


  {


  PCRE2_SPTR 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)pcre2_pattern_info(


    re,                       /* the compiled pattern */


    PCRE2_INFO_NAMETABLE,     /* address of the table */


    &name_table);             /* where to put the answer */


  (void)pcre2_pattern_info(


    re,                       /* the compiled pattern */


    PCRE2_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. In the 8-bit library the number is held in two


  bytes, most significant first. */


  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,


      (int)(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.    *
*                                                                        *
* To help with this task, PCRE2 provides the pcre2_next_match() helper.  *
*************************************************************************/
if (!find_all)     /* Check for -g */


  {


  pcre2_match_data_free(match_data);  /* Release the memory that was used */


  pcre2_code_free(re);                /* for the match data and the pattern. */


  return 0;                           /* Exit the program. */


  }
/* Loop for second and subsequent matches */
ovector_last[0] = ovector[0];
ovector_last[1] = ovector[1];
for (;;)


  {


  PCRE2_SIZE start_offset;


  uint32_t options;


  /* After each successful match, we use pcre2_next_match() to obtain the match


  parameters for subsequent match attempts. */


  if (!pcre2_next_match(match_data, &start_offset, &options))


    break;


  /* Run the next matching operation */


  rc = pcre2_match(


    re,                   /* the compiled pattern */


    subject,              /* the subject string */


    subject_length,       /* the length of the subject */


    start_offset,         /* starting offset in the subject */


    options,              /* options */


    match_data,           /* block for storing the result */


    NULL);                /* use default match context */


  /* If this match attempt fails, exit the loop for subsequent matches. */


  if (rc == PCRE2_ERROR_NOMATCH)


    break;


  /* Other matching errors are not recoverable. */


  if (rc < 0)


    {


    printf("Matching error %d\n", rc);


    pcre2_match_data_free(match_data);


    pcre2_code_free(re);


    return 1;


    }


  /* This demonstration program depends on pcre2_next_match() to ensure that the


  loop for second and subsequent matches does not run forever. However, it would


  be robust practice for a production application to verify this. The following


  block of code shows how to do this. This error case is not reachable unless


  there is a bug in PCRE2.


  Because this program does not set the PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK option,


  the logic is simple. We verify that either ovector[1] has advanced, or that we


  have an empty match touching the end of a previous non-empty match. See the


  API documentation for guidance if your application uses


  PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK and searches for multiple matches. */


  if (!(ovector[1] > ovector_last[1] ||


        (ovector[1] == ovector[0] && ovector_last[1] > ovector_last[0] &&


         ovector[1] == ovector_last[1])))


    {


    printf("\\K was used in an assertion to yield non-advancing matches.\n");


    printf("Run abandoned\n");


    pcre2_match_data_free(match_data);


    pcre2_code_free(re);


    return 1;


    }


  ovector_last[0] = ovector[0];


  ovector_last[1] = ovector[1];


  /* Match succeeded. */


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


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


  should not happen. */


  if (rc == 0)


    printf("ovector was not big enough for all the captured substrings\n");


  /* We guard against patterns such as /(?=.\K)/ that use \K in an assertion to


  set the start of a match later than its end. As explained above, this case


  should not occur because this demonstration program does not set the


  PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK option, however, we do include code showing


  how to detect it. */


  if (ovector[0] > ovector[1])


    {


    printf("\\K was used in an assertion to set the match start after its end.\n"


      "From end to start the match was: %.*s\n", (int)(ovector[0] - ovector[1]),


        (char *)(subject + ovector[1]));


    printf("Run abandoned\n");


    pcre2_match_data_free(match_data);


    pcre2_code_free(re);


    return 1;


    }


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


  also any named substrings. */


  for (i = 0; i < rc; i++)


    {


    PCRE2_SPTR substring_start = subject + ovector[2*i];


    size_t substring_length = ovector[2*i+1] - ovector[2*i];


    printf("%2d: %.*s\n", i, (int)substring_length, (char *)substring_start);


    }


  if (namecount == 0)


    printf("No named substrings\n");


  else


    {


    PCRE2_SPTR 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,


        (int)(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");
pcre2_match_data_free(match_data);
pcre2_code_free(re);
return 0;
}
/* End of pcre2demo.c */