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'The program uses the ON ERROR statement to enable error trapping. The
'program attempts to write a large file to the disk. If an error occurs,
'control is passed to a handling routine, and the ERR function is used to
'determine an appropriate message to display.  The ERROR, ERR, and RESUME
'statements are used to exit the handling routines, and the END, STOP,
'and SYSTEM statements demonstrate ways to exit a program.
 
DECLARE SUB ErrorMessage (Message$)
DECLARE SUB WriteBigFile (Filenum%)
ON ERROR GOTO ErrHandler
CLS
PRINT "This program will attempt to write a large file to a disk drive"
PRINT "you select. The file will be erased when the program ends."
PRINT
DO
    INPUT "Which drive"; DR$
    DR$ = UCASE$(DR$)
LOOP UNTIL LEN(DR$) >= 1 AND LEN(DR$) <= 2 AND DR$ >= "A" AND DR$ <= "Z"
IF LEN(DR$) > 1 THEN
    IF RIGHT$(DR$, 1) <> ":" THEN
        DR$ = LEFT$(DR$, 1) + ":"
    END IF
ELSE
    DR$ = DR$ + ":"
END IF
'Put together a complete file specification.
FileSpec$ = DR$ + "BIGFILE.XXX"
'Get the next available file number.
Filenum% = FREEFILE
'Try to open the file.
OPEN FileSpec$ FOR OUTPUT AS Filenum%
WriteBigFile Filenum%
CLOSE Filenum%
CLS
PRINT "Everything was OK. No errors occurred."
PRINT "Deleting the file that was created."
KILL FileSpec$
'Same as END, returns to operating system.
SYSTEM
 
ErrHandler:
 
SELECT CASE ERR
    CASE 52  'Bad file name or number.
        END
    CASE 53  'File not found.
        RESUME NEXT
    CASE 57  'Device I/O error.
        ErrorMessage "You should probably format the diskette."
        END
    CASE 64  'Bad File Name.
        ErrorMessage "The drive name you specified was not correct."
        END
    CASE 68  'Device unavailable.
        ErrorMessage "The drive you named is unavailable."
        END
    CASE 71  'Drive not ready.
        ErrorMessage "The drive was not ready. Check the drive!"
        END
    CASE ELSE
        ErrorMessage "An unexpected FATAL error has occurred."
        STOP
END SELECT
 
SUB ErrorMessage (Message$)
    ON LOCAL ERROR GOTO MessageError
    CLS
    PRINT Message$
    PRINT "Cannot continue."
    PRINT
    PRINT "Press any key to exit."
    DO
    LOOP WHILE INKEY$ = ""
    EXIT SUB
MessageError:
    RESUME NEXT
END SUB
 
SUB WriteBigFile (Filenum%)
    ON LOCAL ERROR GOTO LocalHandler
    TEXT$ = STRING$(1024, "A")
    FOR I% = 1 TO 400
        PRINT #Filenum%, TEXT$
    NEXT I%
    EXIT SUB
LocalHandler:
    SELECT CASE ERR
        CASE 61             'Disk full.
            ErrorMessage ("There is no room remaining on the disk.")
            KILL "BIGFILE.XXX"
            END
        CASE ELSE
            ERROR ERR
    END SELECT
END SUB