PCRE - Regulárne výrazy v C/C++

Z času na čas sa stretneme s problémom, kedy je potrebné analyzovať reťazce na vyššej úrovni ako len porovnávaním. Tieto situácie sa dajú riešiť vlastným kódom, kedy reťazec pracne analyzujete. V takýchto situáciách jeale výhodnejšie a jednoduhšie použiť regulárne výrazy. Tento článok vám ukáže ako regulárne výrazy implementovať do C/C++ kódu a uvediem aj zopár asi najpoužívanejších príkladov.

Regulárne výrazy

[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}

{0}{123} Translated by ..

\{([0-9]+)\}\{([0-9]+)\}(.+)

Matchovanie v C/C++

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

#define REG_EXP "[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}\\.[0-9]{1,3}"
#define VEC_SIZE 30

int main(int argc, char** argv)
{
   pcre*       re_handle;
   const char* err;
   int         err_offset;
   int         ovector[VEC_SIZE];
   int         res;

   if (argc < 2) {
      printf("USAGE %s [text]\n", argv[0]);
      return 0;
   }

   //kompilacia vyrazu
   re_handle = pcre_compile(REG_EXP, 0, &err, &err_offset, NULL );
   if (!re_handle) {
      printf("ERROR: %s", err);
      return 0;
   }

   //vyhodnotenie vyrazu
   res = pcre_exec(re_handle, NULL, argv[1], strlen(argv[1]), 0, 0, ovector, VEC_SIZE);
   if (res < 0) {
      printf("text is not IP address\n");
   } else {
      printf("text is IP address\n");
   }

   pcre_free(re_handle);
   return 0;
}

-bash-3.00$ ./example1 192.168.1.1
text is IP address

-bash-3.00$ ./example1 slovo
text is not IP address

Počet výskytov a ako získať text vyhovujúci reg. výrazu

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

#define REG_EXP "[0-9]{3}"
#define VEC_SIZE 30

int main(int argc, char** argv)
{
   pcre*       re_handle;
   const char* err;
   int         err_offset;
   int         ovector[VEC_SIZE];
   int         res = 0;
   int         pos = 0;
   int         count = 0;
   char        substring[4];

   if (argc < 2) {
      printf("USAGE %s [text]\n", argv[0]);
      return 0;
   }

   //kompilacia vyrazu
   re_handle = pcre_compile(REG_EXP, 0, &err, &err_offset, NULL );
   if (!re_handle) {
      printf("ERROR: %s", err);
      return 0;
   }

   //prechadzanie stringu a hladanie vyhovujucich substringov
   while ( (res = pcre_exec(re_handle, NULL, argv[1], strlen(argv[1]), pos, 0, ovector, VEC_SIZE)) >= 0 ) {
      count++;
      memcpy(substring, (argv[1] + ovector[0]), (ovector[1] - ovector[0]));
      pos = ovector[1];
      printf("matched %s\n", substring);
   }

   printf("count of 3 decimal numbers:%d\n", count);

   pcre_free(re_handle);
   return 0;
}

-bash-3.00$ ./example2 192.168.1.1
matched 192
matched 168
count of 3 decimal numbers:2

Tajomstvo poľa ovector odhalené - prístup k skupinám

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

#define REG_EXP "\\{([0-9]+)\\}\\{([0-9]+)\\}(.+)"
#define VEC_SIZE 30
#define BUF_SIZE 255

typedef struct {
   int   start;
   int   end;
   char* text;
} subtitle;


int getSubstrFromRe(char* line, int* ovector, int pos, char* out, int out_size)
{
   char* substr_start;
   int   substr_size  = 0;

   substr_start = line + ovector[(2*pos)];
   substr_size  = ovector[(2*pos)+1] - ovector[(2*pos)];
   if (substr_size >= out_size) {
      return 0;
   }

   memset(out, '\0', out_size);
   memcpy(out, substr_start, substr_size);
   return 1;
}

int fillSubtitle(subtitle* sub, pcre* re, char* line)
{
   int   res = 0;
   int   ovector[VEC_SIZE];
   char  buf[BUF_SIZE];

   //vykonanie reg. vyrazu
   res = pcre_exec(re, 0, line, strlen(line), 0, 0, ovector, VEC_SIZE);
   if (res < 0) {
      return 0;
   }

   //spracovanie start-u
   getSubstrFromRe(line, ovector, 1, buf, BUF_SIZE);
   sub->start = atoi(buf);

   //spracovanie end-u
   getSubstrFromRe(line, ovector, 2, buf, BUF_SIZE);
   sub->end = atoi(buf);

   //spracovanie textu
   getSubstrFromRe(line, ovector, 3, buf, BUF_SIZE);
   sub->text = malloc(strlen(buf));
   strcpy(sub->text, buf);

   return 1;
}

int main(int argc, char** argv)
{
   FILE*       subtitle_file = NULL;
   pcre*       re_handle     = NULL;
   pcre_extra* re_extra      = NULL;
   const char* err;
   int         err_offset;
   char        buf[BUF_SIZE];
   subtitle    sub;

   if (argc < 2) {
      printf("USAGE %s [subtitle file]\n", argv[0]);
      return 0;
   }

   //kompilacia reg.vyrazu
   re_handle = pcre_compile(REG_EXP, 0, &err, &err_offset, NULL );
   if (!re_handle) {
      printf("ERROR reg.exp.: %s", err);
      return 0;
   }

   subtitle_file = fopen(argv[1], "r");
   while ( fgets (buf, BUF_SIZE, subtitle_file) != NULL ) {
      if (fillSubtitle(&sub, re_handle, buf)) {
         printf("line info:\n");
         printf(" -start:%d\n", sub.start);
         printf(" -end:%d\n", sub.end);
         printf(" -text:%s\n", sub.text);
         free(sub.text);
      }
   }

   fclose(subtitle_file);
   pcre_free(re_handle);
   return 0;
}