Regular expression pattern match in a string, I only checked with * as wild card, other wild card characters are easy implement but I havent done that.

any problems you can email me @ rramaswa@usc.edu

platform - Unix/Linux, havent tested in windows, should'nt be a problem unless some standard header files are missing.

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

int index;

int main()
{
  char *reg_str,*str;
  int flag = 0;
  int reg_index = 0;
  int i = 0;
  int reg_len = 0;
  int *arr;
  int arr_count = 0;
  int reg_flag = 0;
  int Find_Match(char c,int flag, char *str,int *arr, int *arr_count);

  reg_str = (char *)malloc(100);
  str = (char *)malloc(100);
  arr = (int *)malloc(100 *sizeof(int));
  index = 0;
  printf("Enter the regular expression ..\n");
  gets(reg_str);
  printf("\nEnter the string ..\n");
  gets(str);
  reg_len = strlen(reg_str);
  
  for(i = 0;i < reg_len;i++)
    {
      if(reg_str[i] == '*')
	{
	  //reg_index++;
	  flag = 1;
	  free(arr);
	  arr_count = 0;
	}
      else
	{
	  if(Find_Match(reg_str[i],flag,str,arr,&arr_count) == 0)
	    {
	      printf("pattern not found ...\n");
	      reg_flag = 1;
	      break;
	    }
	}
    }
  if(reg_flag == 0)
    printf("reg exp pattern found in the string ..\n");
  return 0;
}

int Find_Match(char c,int flag, char *str,int *arr, int *arr_count)
{
  int i = 0;
  int counter = 0;
  int arr_index = 0;

  if(flag == 0)
    {
      if(str[index] == c)
	{
	  index++;
	  return 1;
	}
      else 
	{
	  return 0;
	}
    }

  else
    {
      if(*arr_count == 0)
	{
	  for(i = index;str[i] != '\0';i++)
	    {
	      if(str[i] == c)
		{
		  arr[*arr_count] = i;
		  *arr_count = *arr_count + 1;
		  if(counter == 0)
		    {
		      index++;
		      counter++;
		    }
		}
	    }
	}
      else
	{
	  for(i = 0;i < *arr_count;i++)
	    {
	      if(arr[i] == -1)
		continue;
	      arr_index = arr[i] + 1;
	      if(str[arr_index] == c)
	      {
		arr[i] = arr_index;
		if(counter == 0)
	        {
		  index = arr_index + 1;
		  counter++;
		}
	      }
	      else
	      {
		arr[i] = -1;
	      }
	   }
	}
    }
   if(counter == 0)
     return 0;
   else
     return 1;
}

Dont use "gets( )" for accepting string input from user -- It is a bad programming practice and the function itself is flawed as it doesnt check for buffer overflows. Use [search]fgets( )[/search] instead.

Avoid use of globals if possible -- there is no condition where the program cant be done without using globals. Using globals prevents your algo or program being used as a part of a larger program.