struct re_pattern_buffer
{
/* [[[begin pattern_buffer]]] */
	/* Space that holds the compiled pattern.  It is declared as
          `unsigned char *' because its elements are
           sometimes used as array indexes.  */
  unsigned char *buffer;

	/* Number of bytes to which `buffer' points.  */
  unsigned long allocated;

	/* Number of bytes actually used in `buffer'.  */
  unsigned long used;	

        /* Syntax setting with which the pattern was compiled.  */
  reg_syntax_t syntax;

        /* Pointer to a fastmap, if any, otherwise zero.  re_search uses
           the fastmap, if there is one, to skip over impossible
           starting points for matches.  */
  char *fastmap;

        /* Either a translate table to apply to all characters before
           comparing them, or zero for no translation.  The translation
           is applied to a pattern when it is compiled and to a string
           when it is matched.  */
  char *translate;

	/* Number of subexpressions found by the compiler.  */
  size_t re_nsub;

        /* Zero if this pattern cannot match the empty string, one else.
           Well, in truth it's used only in `re_search_2', to see
           whether or not we should use the fastmap, so we don't set
           this absolutely perfectly; see `re_compile_fastmap' (the
           `duplicate' case).  */
  unsigned can_be_null : 1;

        /* If REGS_UNALLOCATED, allocate space in the `regs' structure
             for `max (RE_NREGS, re_nsub + 1)' groups.
           If REGS_REALLOCATE, reallocate space if necessary.
           If REGS_FIXED, use what's there.  */
#define REGS_UNALLOCATED 0
#define REGS_REALLOCATE 1
#define REGS_FIXED 2
  unsigned regs_allocated : 2;

        /* Set to zero when `regex_compile' compiles a pattern; set to one
           by `re_compile_fastmap' if it updates the fastmap.  */
  unsigned fastmap_accurate : 1;

        /* If set, `re_match_2' does not return information about
           subexpressions.  */
  unsigned no_sub : 1;

        /* If set, a beginning-of-line anchor doesn't match at the
           beginning of the string.  */ 
  unsigned not_bol : 1;

        /* Similarly for an end-of-line anchor.  */
  unsigned not_eol : 1;

        /* If true, an anchor at a newline matches.  */
  unsigned newline_anchor : 1;

/* [[[end pattern_buffer]]] */
};

typedef struct re_pattern_buffer regex_t;

int regcomp (regex_t *preg, const char *regex, int cflags);

int regexec (const regex_t *preg, const char *string, size_t nmatch, regmatch_t pmatch[], int eflags);

size_t regerror (int errcode, const regex_t *preg, char *errbuf, size_t errbuf_size);

void regfree (regex_t *preg);

a

egu

[mt]oi

[abcdefghijklmnopqrstuvwxyz]

[a-z]

[a]{3}

^[A-Z]

^www\.[-_[:alnum:]]+\.[[:lower:]]{2,4}

^www\.

^[w]{3}\.

[-_[:alnum:]]+

\.

[[:lower:]]{2,4}

"www\\.[-_[:alnum:]]+\\.[[:lower:]]{2,4}"

#include <stdio.h>
#include <stdlib.h>
#include <regex.h>

int main (void)
{
   int err;
   regex_t preg;
   const char *str_request = "www.developpez.com";
   const char *str_regex = "www\\.[-_[:alnum:]]+\\.[[:lower:]]{2,4}";

/* (1) */
   err = regcomp (&preg, str_regex, REG_NOSUB | REG_EXTENDED);
   if (err == 0)
   {
      int match;

/* (2) */
      match = regexec (&preg, str_request, 0, NULL, 0);
/* (3) */
      regfree (&preg);
/* (4) */
      if (match == 0)
      {
         printf ("%s est une adresse internet valide\n", str_request);
      }
/* (5) */
      else if (match == REG_NOMATCH)
      {
         printf ("%s n\'est pas une adresse internet valide\n", str_request);
      }
/* (6) */
      else
      {
         char *text;
         size_t size;

/* (7) */
         size = regerror (err, &preg, NULL, 0);
         text = malloc (sizeof (*text) * size);
         if (text)
         {
/* (8) */
            regerror (err, &preg, text, size);
            fprintf (stderr, "%s\n", text);
            free (text);
         }
         else
         {
            fprintf (stderr, "Memoire insuffisante\n");
            exit (EXIT_FAILURE);
         }
      }
   }
   puts ("\nPress any key\n");
/* Dev-cpp */
   getchar ();
   return (EXIT_SUCCESS);
}

"(www\\.[-_[:alnum:]]+\\.[[:lower:]]{2,4})"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <regex.h>

int main (void)
{
   int err;
   regex_t preg;
   const char *str_request = "http://www.developpez.net/forums/index.php";
   const char *str_regex = "(www\\.[-_[:alnum:]]+\\.[[:lower:]]{2,4})";

/* (1) */
   err = regcomp (&preg, str_regex, REG_EXTENDED);
   if (err == 0)
   {
      int match;
      size_t nmatch = 0;
      regmatch_t *pmatch = NULL;
      
      nmatch = preg.re_nsub;
      pmatch = malloc (sizeof (*pmatch) * nmatch);
      if (pmatch)
      {
/* (2) */
         match = regexec (&preg, str_request, nmatch, pmatch, 0);
/* (3) */
         regfree (&preg);
/* (4) */
         if (match == 0)
         {
            char *site = NULL;
            int start = pmatch[0].rm_so;
            int end = pmatch[0].rm_eo;
            size_t size = end - start;
               
            site = malloc (sizeof (*site) * (size + 1));
            if (site)
            {
               strncpy (site, &str_request[start], size);
               site[size] = '\0';
               printf ("%s\n", site);
               free (site);
            }
         }
/* (5) */
         else if (match == REG_NOMATCH)
         {
            printf ("%s n\'est pas une adresse internet valide\n", str_request);
         }
/* (6) */
         else
         {
            char *text;
            size_t size;

/* (7) */
            size = regerror (err, &preg, NULL, 0);
            text = malloc (sizeof (*text) * size);
            if (text)
            {
/* (8) */
               regerror (err, &preg, text, size);
               fprintf (stderr, "%s\n", text);
               free (text);
            }
            else
            {
               fprintf (stderr, "Memoire insuffisante\n");
               exit (EXIT_FAILURE);
            }
         }
      }
      else
      {
         fprintf (stderr, "Memoire insuffisante\n");
         exit (EXIT_FAILURE);
      }
   }
   puts ("\nPress any key\n");
/* Dev-cpp */
   getchar ();
   return (EXIT_SUCCESS);
}