/* A sample program to show the use of fseek and ftell.  The program will
carry out a binary search on a the master file. Author: Goldine Cupit.*/



#include <stdio.h>
#define REC_LEN 167
#define KEY_LEN 9

main() {
   FILE *fp;
   int first,last,count,mid,recCount;
   char recordKey[REC_LEN];  // The key at the current file position.
   char searchKey[] = "000000028"; // Hard coded value of the key value 
                                   // we are looking for.

   // The file to be searched is called master.
   if ((fp = fopen("master","r")) ==NULL) { 
      printf("Problem opening file master\n");
      exit(1);
      }
   else {
      // We must determine the number of records in the file.  
      // Use fseek to move the file position to the last byte in the file.
      fseek(fp,0,SEEK_END);

      // Use ftell to obtain this byte count.
      count = ftell(fp);

      //Compute the number of records in the file
      recCount = count/REC_LEN;

      first = 0;
      last = recCount - 1;

      //Binary search using the algorithm from A58.
      //As written, we assume that the search searchKey is in the list.
      while ( first != last){
	 mid = (first + last) / 2;
	 //Move the file position to the middle record.
	 fseek(fp, mid*REC_LEN,SEEK_SET);

         //Read the key field only
	 fscanf(fp,"%9s",recordKey);

	 if (strncmp(searchKey,recordKey,KEY_LEN) <= 0) 
	    last = mid;
         else 
	    first = mid + 1;
	 }

	 printf("the index is  %d\n",first);
	 }
}