Radio Shack TRS-80 Owner's Manual page 171

\m\
DISK BASIC
sSBBESj*
Random
Access:
A
General
Procedure
The
previous
example shows
the
necessary sequences
to
read and
write using
random
access.
But
it
does not demonstrate
the
primary advantages of
this
form
of access
—
in particular,
it
doesn't
show
how
to
update existing
files
by going
directly to the desired record.
The
program below,
glossacc/bas,
develops
the glossary
example
to
show
some
of the
techniques of
random
access
for
file
maintenance.
But
before
looking
at the
program,
study
this
general
procedure
for creating
and
maintaining
files
via
random
access.
Step
See
GLOSSACC/BAS,
Line
Number
1.
Open
the
file
110
2.
Field
the
buffer
120
3.
Get
the record
to
be updated 140
4.
Display current contents
of
the record (use
145-170
CVD,
CVl,
CVS
before displaying numeric
data)
5.
LSET
and
RSET
new
values
into
the
fields
210-230
(use
MKD$,
MKI$,
MKS$
with
numeric data
before setting
it
into
the
buffer)
6.
PUT
the
updated
record
240
7.
To update another
record,
continue
at
step
3.
250-260
Otherwise,
go
to
step
8.
8.
Close
the
file
270
10
REM .,,,..
GLOSSACC/BAS
.
,.
100 CLS
:
CLEAR 300
110 OPEN "R"»
1.
"GL0SSARY/BAS"
120
FIELD
1»
IB AS WD*
,
238 AS
MEANING**
2
AS NX*
130 INPUT "WHAT RECORD DO YOU WANT
TO ACCESS'
1
!
R%
140 GET
1 ,
RI
145 HXl
=
GUI (NX*)
'SAVE LINK TO NEXT
ALPHABETICAL ENTRY
150
PRINT "WORD
;
"WD$
160
PRINT "DEF'N
:
"
;
PRINT MEANING*
170
PRINT "NEXT ALPHABETICAL ENTRY; RECORD
»:"
NX!
:
PRINT
180 W$
=
""
:
INPUT "TYPE NEW WORD <ENTER>
OR <ENTER>
IF
OK"
5
W*
190 D*
=
""
;
PRINT "TYPE NEW DEF'N
<
ENTER
>
OR
<ENTER>
IF
OK?"
;
LINE INPUT D$
200 INPUT "TYPE NEW SEQUENCE NUMBER
OR
<ENTER>
IF
OK"? NXI
210
IF
W$ <>
""
THEN LSET WD*
= W*
220
IF D* <>
""
THEN LSET MEANING*
=
D$
153