Commodore 1581 - Completing Relative File Creation

inputs a record number and converts it into the required low-byte/
high-byte form:
450 INPUTRECORD NUMBER DESIRED";RE
460 IF RE<1 OR RE>65535 THEN 450
470RH = INT(RE/256)
480RL = RE-256*RH
490 PRINT#15, "P" +CHR$(98) + CHR$(RL) + CHR$(RH)
Assuming RH and RL are calculated as in the previous example,
programs may also use variables for the channel, record, and offset
required:
570 INPUT "CHANNEL, RECORD, & OFFSET DESIRED";CH,RE,OF
630 PRINT#15, "P" + CHR$
(CH + 96) + CHR$(RL) + CHR$(RH) + CHR$(OF)
COMPLETING RELATIVE FILE CREATION
Now that you have learned how to use both the Open and Re-
cord# commands, you are almost ready to properly create a relative
file. The only additional fact you need to know is that CHR$(255) is a
special character in a relative file. It is the character used by the DOS to
fill relative records as they are created, before a program fills them
with other information. Thus, if you want to write the last record, you
expect to need in your file with dummy data that will not interfere with
your later work, CHR$(255) is the obvious choice. Here is how it works
in an actual program which you may copy for use in your own relative
file programs.
BASIC 2.0:
1020 OPEN 15,8,15 Open command channel
1380 INPUT'ENTER RELATIVE FILE NAME";FI$ Select file parameters
1390 INPUT'ENTER MAX. # OF RECORDS";NR
1400 INPUT'ENTER RECORD LENGTH";RL
1410 OPEN l,8,2,"0:" + FI$ + "JL," + CHR$(RL) Begin to create desired
file
1420 GOSUB 59990 Check for disk errors
1430 RH = INT(NR/256) Calculate length values
144ORL = NR-256*RH
1450 PRINT#15,"P" + CHR$(96 + 2) +
CHR$(RL) + CHR$(RH) Position to last record
number
1455 PRINT#15,"P" + CHR$(96 + 2) + Re-position for safety
CHR$(RL) + CHR$(RH)
1460 GOSUB 59990
1470 PRINT#1 ,CHR$(255); Send default character to
it
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