Radio Shack TRS-80 Owner's Manual page 169

DISK BASIC
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The
buffer
is
a waiting area for the data.
Before
writing data
to
a
file,
you must
place
it
in the
buffer
assigned
to
the
file.
After reading data
from
a
file,
you
must
retrieve
it
from
the buffer.
As you can
see
from
the
sample put and get statements above, data
is
passed
to
and
from
the
disk
in
records.
The
size
of
each record
is
determined
by an
Open
statement.
Storing
Data
In
a Buffer
You must
place the entire
record
into the buffer
before putting
its
contents into
the disk
file.
This
is
accomplished by
1)
dividing the buffer
up
into fields
and
naming
them,
then
2)
placing the string or
numeric
data
into the
fields.
For example, suppose
we
want
to store
a glossary
on
disk.
Each
record will
consist
of a
word
followed
by
its
definition.
We
start
with:
100
0PEN"R"»
1>
"GLOSSARY/BAB"
110
FIELD
1, IB
AS
WD$t 240 AS
MEANING*
Line 100 opens a
file
named
glossary/bas
(creates
it
if
it
doesn't already exist);
and gives buffer
1
direct
access
to
the
file.
Line 110
defines
two
fields
onto buffer
1:
wd$
consists
of the
first
16 bytes
of the buffer;
meanings
consists
of the
last
240
bytes.
wd$
and
meanings
are
now
field-names
What makes
field
names
different?
Most
string
variables point
to
an
area in
memory
called the string
space.
This
is
where
the
value of the string
is
stored.
Field
names, on
the
other
hand, point
to
the buffer area
assigned
in
the
held
statement.
So, for
example,
the statement:
10
PRINT WD*5 ":"
i
MEANING*
displays the contents of the
two
buffer
fields
defined above.
These values
are
meaningless unless
we
first
place data in
the buffer, lset,
rset
and
get can
all
be used
to
accomplish
this
function.
We'll
start
with
lset and
rset,
which
are
used
in
preparation for
disk output.
Our
first
entry
is
the
word
"left-justify"
followed
by
its
definition.
100
0PEN"R"»
1»
"GLOSSARY/BAS"
110
FIELD
1»
IS
AS WD*, 240 AS
MEANING*
120
LSET
WD*="LEFT-JUSTIFY"
130
LSET
MEANING*="T0
PLACE
A
VALUE
IN
A
FIELD FROM LEFT TO
RIGHT1
IF
THE DATA
DOESN'T FILL THE
FIELD, BLANKS
ARE
ADDED
ON THE
RIGHT?
IF
THE DATA
IS
TOO LONG, THE EXTRA
151