cc.c

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/**
 * cc - Char Counter. Finds the n'th character in a file and displays it
 *      together with some surrounding characters.
 */

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

int main(int argc, char* argv[])
{
   int   ch;
   int   num;
   int   pos; /* The character we are looking for */
   int   sur; /* Number of surrounding characters */
   FILE *instream;

   /* Check the number of arguments */
   if ((argc != 3) && (argc != 4))
   {
      fprintf(stderr, "Usage: cc filename char# [#surrounding chars]\n");
      return EXIT_SUCCESS;
   }

   /* Read arguments */
   if (argc == 4)
     sur = atoi(argv[3]);
   else
     sur = 50;

   num = atoi(argv[2]);

   if (!(instream = fopen(argv[1], "r")))
   {
      fprintf(stderr, "Can't open file '%s'\n", argv[1]);
      return EXIT_FAILURE;
   }

   pos = 0;

   /* Go through the file character by character */
   while ((ch = fgetc(instream)) != EOF)
   {
      /* The character we are looking for */
      if (pos == num)
         printf(" >> %c << ", ch);

      /* Also print some surrounding characters */
      else if (abs(pos - num) < sur)
         printf("%c", ch);

      pos++;
   }
   printf("\n");

   /* The file was not big enough */
   if (num > pos)
      fprintf(stderr, "File is not more than %d characters long\n", pos);

   /* fclose might fail, but since the program ends here we really
    * don't care. */
   (void)fclose(instream);

   return EXIT_SUCCESS;
}