Commodore 1541-II - Expanding a Relative File

1410OPEN l,8,2,4t0:"+FI$+",L,"
1420 GOSUB 59990
1430RH = INT(NR/256)
1440RL = NR-256*RH
1450PRINT#15,t4P" + CHR$(96 + 2) +
CHR$(RL) + CHR$(RH)
1460 GOSUB 59990
1470 PRINT#1,CHR$(255);
1480 GOSUB 59990
1490PRINT#15/'P" + CHR$(96 + 2) +
CHR$(RL) + CHR$(RH)
1500 GOSUB 59990
1510 CLOSE 1
1520 GOSUB 59990
9980 CLOSE 15
9990 END
59980 REM CHECK DISK SUBROUTINE
59990 INPUT#15,EN,EM$,ET,ES
60000 IF EN>1 AND ENO50 THEN PRINT
EN,EM$,ET,ES:STOP
60010 RETURN
Begin to create desired file
Check for disk errors
Calculate length values
Position to last record
number
Send default character to it
Re-position for safety
Now the file can be safely
closed
And the command channel
closed
Before we end the pro
gram
Ignore "RECORD NOT
PRESENT"
Two lines require additional explanation. When line 1470 executes, the disk drive will
operate for up to ten or more minutes, creating all the records in the file, up to the
maximum record number you selected in line 1390. This is normal, and only needs to be
done once. During the process you may hear the drive motor turning and an occasional
slight click as the head steps from track to track, everything is probably just fine. Second,
line 60000 above is different from the equivalent line in the error check subroutine given
earlier. Here disk error number 50 is specifically ignored, because it will be generated
when the error channel is checked in line 1460. We ignore it because not having a
requested record would only be an error if that record had previously been created.
EXPANDING A RELATIVE FILE
What if you underestimate your needs and need to expand a relative file later? No
problem. Simply request the record number you need, even if it doesn't currently exist in
the file. If fthere is no such record yet, DOS' will create it as soon as you try to write
information in it, and also automatically create any other missing records below it in
number. The only penalty will be a slight time delay while the records are created.
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