fig11_12.c

C程序设计经典教程第5版程序示例,比较适合初级c语言的学生

/* Fig. 11.12: fig11_12.c
   Writing to a random access file */
#include <stdio.h>

/* clientData structure definition */
struct clientData { 
   int acctNum;          /* account number */
   char lastName[ 15 ];  /* account last name */
   char firstName[ 10 ]; /* account first name */
   double balance;       /* account balance */
}; /* end structure clientData */
 
int main( void ) 
{ 
   FILE *cfPtr; /* credit.dat file pointer */

   /* create clientData with default information */
   struct clientData client = { 0, "", "", 0.0 };

   /* fopen opens the file; exits if file cannot be opened */
   if ( ( cfPtr = fopen( "credit.dat", "rb+" ) ) == NULL ) {
      printf( "File could not be opened.\n" );
   } /* end if */
   else { 

      /* require user to specify account number */
      printf( "Enter account number"
         " ( 1 to 100, 0 to end input )\n? " );
      scanf( "%d", &client.acctNum );

      /* user enters information, which is copied into file */
      while ( client.acctNum != 0 ) { 

         /* user enters last name, first name and balance */
         printf( "Enter lastname, firstname, balance\n? " );
        
         /* set record lastName, firstName and balance value */
         fscanf( stdin, "%s%s%lf", client.lastName, 
            client.firstName, &client.balance );

         /* seek position in file to user-specified record */
         fseek( cfPtr, ( client.acctNum - 1 ) * 
            sizeof( struct clientData ), SEEK_SET );

         /* write user-specified information in file */
         fwrite( &client, sizeof( struct clientData ), 1, cfPtr );

         /* enable user to input another account number */
         printf( "Enter account number\n? " );
         scanf( "%d", &client.acctNum );
      } /* end while */

      fclose( cfPtr ); /* fclose closes the file */
   } /* end else */

   return 0; /* indicates successful termination */

} /* end main */
 


/**************************************************************************
 * (C) Copyright 1992-2007 by Deitel & Associates, Inc. and               *
 * Pearson Education, Inc. All Rights Reserved.                           *
 *                                                                        *
 * DISCLAIMER: The authors and publisher of this book have used their     *
 * best efforts in preparing the book. These efforts include the          *
 * development, research, and testing of the theories and programs        *
 * to determine their effectiveness. The authors and publisher make       *
 * no warranty of any kind, expressed or implied, with regard to these    *
 * programs or to the documentation contained in these books. The authors *
 * and publisher shall not be liable in any event for incidental or       *
 * consequential damages in connection with, or arising out of, the       *
 * furnishing, performance, or use of these programs.                     *
 *************************************************************************/