Writing The Record - Commodore 1541 User Manual

between maximum field length and average field length. A program that uses v .
record lengths must calculate the total length of each record as it is entered , to
be
8
total of all fields doesn't exceed the space available. Ure
WRITING THE RECORD
Here is an example of program lines to enter variable length fields for the
abov
design , build them into a single string, and send them to record number RE in file
nuc
3 (assumed to be a relative file that uses channel number 3) .
150 CR$=CHR$(13)
2000 INPUT"NAME";NA$
2010 IF LEN(NA$)>30 THEN 2000
2020 lNPUT"STREET" ;SA$
2030 IF LEN(SA$)>30 THEN 2020
2040 INPUT"CITY & STATE";CS$
2050 lF LEN(CS$)>25 THEN 2040
2060 lNPUT"ZIP CODE" ;ZP$
2070 lF LEN(ZP$)> 10 THEN 2060
2080 DA$ = NA$+ CR$+ SA$+ CR$+
CS$+ CR$ + ZP$
2090 lF LEN(DA$)<87 THEN 2120
2100 PRINT"RECORD TOO LONG"
2110 GOTO 2000
2120 RH= INT(RE/256)
2130 RL=RE-256*RH
Carriage Return
Enter fields
And check length of each
Build output data string
Check its length
If too long overall
Calculate record number
' J f1J_
IF LEN(SA$)>27 THEN 2020
~SA$=
SA$+ LEFT$(BL$ ,27-LN)
fl' I J
(NPUT"CITY & STATE";CS$
~
LN = LEN(CS$)
;,so
IF LEN(CS$)>23 THEN 2040
j,sS
CS$ = CS$+ LEFT$(BL$ ,23 -LN)
~
INPUT"ZIP CODE" ;ZP$
' f lJS
LN = LEN(ZP$)
f10IFLEN(ZP$)>10 THEN 2060
~S
ZP$ = ZP$ + LEFT$(BL$ , 10-LN)
~
DA$ =NA$+ SA$+ CS$+ ZP$
:120
RH= lNT(RE/256)
' . 1J0
RL
= RE-256*RH
;,40 PRINT#15, "P" +CHR$(96 + 3) +
. CHR$(RL) + CHR$(RHl + CHR$ (I)
!ISO GOSUB 59990
!160 PRINT# 3 ,DA$ ;
:170
GOSUB 59990
!i80 PRINT#l5 ,"P" +CHR$(96+3) +
CHR$(RL) + CHR$(RH) + CHR$
(I)
:190
GOSUB 59990
Note lack of separators
Note added semicolon
If
field contents vary in length , variable field lengths are often preferable . On the
' C her hand , if the field lengths are stable, fixed field lengths are preferable . Fixed length
ields are
also required if you want to use the optional offset parameter of the Record#
;oounand to point at a particular byte within a record . However, one warning must be
13dc
about using the offset this way . When any part of a record is written , DOS
2140 PRINT#l5,"P" +CHR$(96+3)+
CHR$(RL) + CHR$(RH)
2150 GOSUB 59990
vcrwrites any remaining spaces in the record . Thus, if you must use the offset option,
Position to record
number RE
:ever
update any field in a record other than the last one unless all succeeding fields will
Check for disk errors
ilsobe
updated from memory later.
2160 PRINT#3,DA$
2170 GOSUB 59990
2180 PRlNT#l5,"P" +CHR$(96+3)+
CHR$(RL) + CHR$(RH)
2190 GOSUB 59990
Send data to it . The above programs are careful to match record lengths exactly to the space
•11ilable. Programs that don't do so will discover that DOS pads short records out to full
Re-position for safety
1
1.e
with fill characters, and tri.mcates overlong records to fill only their allotted space.
Yihen a
record is truncated, DOS will indicate error 51, "RECORD OVERFLOW", but
~records
will be accepted without a DOS error message .
To use the above program lines for the version with fixed length fields, we
YI
•~·-
alter a few lines as follows :
""'WING A RELATIVE RECORD
150
160 BL$="
2000 INPUT"NAME";NA$
2005 LN = LEN(NA$)
2010 IF LEN(NA$) > 27 THEN 2000
2015 NA$ = NA$+LEFT$(BL$ ,27-LN)
2020 JNPUT" STREET";SA$
2025 LN = LEN(SA$)
62
Not needed this time
27 shifted space characters
Checking for different tengthl
And padding to preset sizes
Once
a relative record has been written properly to diskette, reading it back into
-lllputer memory is fairly simple, but the procedure again varies , depending on whether
illes fixed or variable length fields . Here are the program lines needed to read back the
lllable fields created above from record number RE in file and channel 3:
~RH=
INT(RE/256)
llO
RL
= RE-256*RH
120
PiUNT#l5, "P" + CHR$(96 + 3)+
CJ.iRS(RL) + CHR$(RH) + CHR$ ( 1)
63
Calculate record number
Position to record number RE