c语言大学教程(第六版)源程序

/* Fig. 11.16: fig11_16.c This program reads a random access file sequentially, updates data already written to the file, creates new data to be placed in the file, and deletes data previously in the 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 */ /* prototypes */ int enterChoice( void ); void textFile( FILE *readPtr ); void updateRecord( FILE *fPtr ); void newRecord( FILE *fPtr ); void deleteRecord( FILE *fPtr ); int main( void ) { FILE *cfPtr; /* credit.dat file pointer */ int choice; /* user's choice */ /* 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 { /* enable user to specify action */ while ( ( choice = enterChoice() ) != 5 ) { switch ( choice ) { /* create text file from record file */ case 1: textFile( cfPtr ); break; /* update record */ case 2: updateRecord( cfPtr ); break; /* create record */ case 3: newRecord( cfPtr ); break; /* delete existing record */ case 4: deleteRecord( cfPtr ); break; /* display message if user does not select valid choice */ default: printf( "Incorrect choice\n" ); break; } /* end switch */ } /* end while */ fclose( cfPtr ); /* fclose closes the file */ } /* end else */ return 0; /* indicates successful termination */ } /* end main */ /* create formatted text file for printing */ void textFile( FILE *readPtr ) { FILE *writePtr; /* accounts.txt file pointer */ /* create clientData with default information */ struct clientData client = { 0, "", "", 0.0 }; /* fopen opens the file; exits if file cannot be opened */ if ( ( writePtr = fopen( "accounts.txt", "w" ) ) == NULL ) { printf( "File could not be opened.\n" ); } /* end if */ else { rewind( readPtr ); /* sets pointer to beginning of file */ fprintf( writePtr, "%-6s%-16s%-11s%10s\n", "Acct", "Last Name", "First Name","Balance" ); /* copy all records from random-access file into text file */ while ( !feof( readPtr ) ) { fread( &client, sizeof( struct clientData ), 1, readPtr ); /* write single record to text file */ if ( client.acctNum != 0 ) { fprintf( writePtr, "%-6d%-16s%-11s%10.2f\n", client.acctNum, client.lastName, client.firstName, client.balance ); } /* end if */ } /* end while */ fclose( writePtr ); /* fclose closes the file */ } /* end else */ } /* end function textFile */ /* update balance in record */ void updateRecord( FILE *fPtr ) { int account; /* account number */ double transaction; /* transaction amount */ /* create clientData with no information */ struct clientData client = { 0, "", "", 0.0 }; /* obtain number of account to update */ printf( "Enter account to update ( 1 - 100 ): " ); scanf( "%d", &account ); /* move file pointer to correct record in file */ fseek( fPtr, ( account - 1 ) * sizeof( struct clientData ), SEEK_SET ); /* read record from file */ fread( &client, sizeof( struct clientData ), 1, fPtr ); /* display error if account does not exist */ if ( client.acctNum == 0 ) { printf( "Acount #%d has no information.\n", account ); } /* end if */ else { /* update record */ printf( "%-6d%-16s%-11s%10.2f\n\n", client.acctNum, client.lastName, client.firstName, client.balance ); /* request transaction amount from user */ printf( "Enter charge ( + ) or payment ( - ): " ); scanf( "%lf", &transaction ); client.balance += transaction; /* update record balance */ printf( "%-6d%-16s%-11s%10.2f\n", client.acctNum, client.lastName, client.firstName, client.balance ); /* move file pointer to correct record in file */ fseek( fPtr, ( account - 1 ) * sizeof( struct clientData ), SEEK_SET ); /* write updated record over old record in file */ fwrite( &client, sizeof( struct clientData ), 1, fPtr ); } /* end else */ } /* end function updateRecord */ /* delete an existing record */ void deleteRecord( FILE *fPtr ) { struct clientData client; /* stores record read from file */ struct clientData blankClient = { 0, "", "", 0 }; /* blank client */ int accountNum; /* account number */ /* obtain number of account to delete */ printf( "Enter account number to delete ( 1 - 100 ): " ); scanf( "%d", &accountNum ); /* move file pointer to correct record in file */ fseek( fPtr, ( accountNum - 1 ) * sizeof( struct clientData ), SEEK_SET ); /* read record from file */ fread( &client, sizeof( struct clientData ), 1, fPtr ); /* display error if record does not exist */ if ( client.acctNum == 0 ) { printf( "Account %d does not exist.\n", accountNum ); } /* end if */ else { /* delete record */ /* move file pointer to correct record in file */ fseek( fPtr, ( accountNum - 1 ) * sizeof( struct clientData ), SEEK_SET ); /* replace existing record with blank record */ fwrite( &blankClient, sizeof( struct clientData ), 1, fPtr ); } /* end else */ } /* end function deleteRecord */ /* create and insert record */ void newRecord( FILE *fPtr ) { /* create clientData with default information */ struct clientData client = { 0, "", "", 0.0 }; int accountNum; /* account number */ /* obtain number of account to create */ printf( "Enter new account number ( 1 - 100 ): " ); scanf( "%d", &accountNum ); /* move file pointer to correct record in file */ fseek( fPtr, ( accountNum - 1 ) * sizeof( struct clientData ), SEEK_SET ); /* read record from file */ fread( &client, sizeof( struct clientData ), 1, fPtr ); /* display error if account already exists */ if ( client.acctNum != 0 ) { printf( "Account #%d already contains information.\n", client.acctNum ); } /* end if */ else { /* create record */ /* user enters last name, first name and balance */ printf( "Enter lastname, firstname, balance\n? " ); scanf( "%s%s%lf", &client.lastName, &client.firstName, &client.balance ); client.acctNum = accountNum; /* move file pointer to correct record in file */ fseek( fPtr, ( client.acctNum - 1 ) * sizeof( struct clientData ), SEEK_SET ); /* insert record in file */ fwrite( &client, sizeof( struct clientData ), 1, fPtr ); } /* end else */ } /* end function newRecord */ /* enable user to input menu choice */ int enterChoice( void ) { int menuChoice; /* variable to store user's choice */ /* display available options */ printf( "\nEnter your choice\n" "1 - store a formatted text file of acounts called\n" " \"accounts.txt\" for printing\n" "2 - update an account\n" "3 - add a new account\n" "4 - delete an account\n" "5 - end program\n? " ); scanf( "%d", &menuChoice ); /* receive choice from user */ return menuChoice; } /* end function enterChoice */ /*************