Radio Shack TRS-80 Trsdos & Disk Basic Reference Manual page 133

DISK BASIC
Random
Access Statements
FIELD
(organize a
random
file-buffer into fields)
FIELD
nmexp,nmexpl
AS
varl$ [,nmexp2
AS
var2$
. .
.]
where
nmexp
specifies a
random
access
file
buffer,
nmexp=\,2,
... ,15
nmexpl
specifies
the length
of
the
first
field,
varl$
defines
a
variable
name
for
the
first field
nmexp2
specifies
the length
of
the
second
field
var2$
defines
a
variable
name
for
the second
field
subsequent
nmexp AS
var$
pairs
define
other
fields in
the buffer
Before
FIELDing
a buffer,
you must
use an
OPEN
statement
to
assign that
buffer to
a particular disk
file
(must
use
random
access
mode).
Then
use the
FIELD
statement
to
organize
a
random
file
buffer so that
you
can
pass data
from
BASIC
to disk storage
and
vice-versa.
Each random
file
buffer has
255
bytes
which
can
store
data
for
transfer
from
disk storage to
BASIC
or
from
BASIC
to disk.
However, you need
a
way
to access
this
buffer
from
BASIC
so
that
you
can
either
read the data
it
contains or place
new
data
in
it.
The
FIELD
statement provides
the
means
of
access.
You may
use the
FIELD
statement any
number
of times
to
"re-organize" a
file
buffer.
FIELDing
a
buffer does not
clear
the
contents of the
buffer;
only the
means
of
accessing the buffer
(the
field
names)
are changed. Furthermore,
two
or
more
field
names
can reference the
same
area
of
the buffer.
Examples:
FIELD
1,
255 AS R$
This statement
tells
BASIC
to
assign
the
entire
255-byte buffer
to
the
string
variable
A$.
If
you
now
print
A$, you
will see
the contents
of the
buffer.
Of
course,
this
value
would be meaningless
unless
you
have used
GET
to
read
a
255-byte record
from
disk.
Note:
All data
—
both
strings
and numbers
—
must
be placed
into
the buffer
in string
form.
There
are
three
pairs
of
functions
(MKI$/CVI,MKS$/CVS,MKD$/CVD)
for
converting
numbers
to
strings
and
vice-versa.
See "Functions", below.
7-47