Commodore 1541-II - Reading a Relative Record

2030 IF LEN(SA$)>27 THEN 2020
2035 SA$ = SA$ + LEFT$(BL$,27-LN)
2040 INPUT"CITY & STATE";CS$
2045LN = LEN(CS$)
2050 IF LEN(CS$)>23 THEN 2040
2055 CSS = CSS + LEFT$(BL$,23 -LN)
2060 ENfPUT'ZIP CODE";ZP$
2065LN = LEN(ZP$)
2070 IF LEN(ZP$)> 10 THEN 2060
2075 ZP$ = ZP$ + LEFT$(BL$,10-LN)
2080 DAS = NAS + SAS + CSS+ZPS Note lack of separators
2120RH = INT(RE/256)
2130RL = RE-256*RH
2140PRINT#15,"P"+CHR$(96 + 3) +
CHRS(RL) + CHRS(RH)+CHRS (1)
2150 GOSUB 59990
2160 PRINT#3 ,DA$; Note added semicolon
2170 GOSUB 59990
2180 PRINT# 15,"P" + CHR$(96 + 3) +
CHRS(RL) + CHRS(RH) + CHRS (1)
2190 GOSUB 59990
If field contents vary in length, variable field lengths are often preferable. On the
other hand, if the field lengths are stable, fixed field lengths are preferable. Fixed length
fields are also required if you want to use the optional offset parameter of the Record#
command to point at a particular byte within a record. However, one warning must be
made about using the offset this way. When any part of a record is written, DOS
overwrites any remaining spaces in the record. Thus, if you must use the offset option,
never update any field in a record other than the last one unless all succeeding fields will
also be updated from memory later.
The above programs are careful to match record lengths exactly to the space
available. Programs that don't do so will discover that DOS pads short records out to full
size with fill characters, and truncates overlong records to fill only their allotted space.
When a record is truncated, DOS will indicate error 51,''RECORD OVERFLOW'', but
short records will be accepted without a DOS error message.
READING A RELATIVE RECORD
Once a relative record has been written properly to diskette, reading it back into
computer memory is fairly simple, but the procedure again varies, depending on whether
it uses fixed or variable length fields. Here are the program lines needed to read back the
variable fields created above from record number RE in file and channel 3:
3000 RH = INT(RE/256) Calculate record number
3010RL = RE-256*RH
3020 PRINT#15,ttP"+CHR$(96 + 3) +
CHRS(RL) + CHR$(RH) + CHRS (1) Position to record number RE
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