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BASIC-80
Disk File
Input/Output
LINE INPUT,
on
the other hand, ignores blanks, commas, and quotation marks,
and reads everything between the current file position and the next carriage return-
line feed,
or
up to
255
characters.
If
the last INPUT did not read to the end of a
logical line, LINE
INPUT
will read to the end
of
that line before reading the next
line. The string
is
assigned to the single string variable specified. In the preceding ex-
ample, assume
that
instead
of
the INPUT statement shown, the following statement
was executed:
LINE INPUT #2,R$
The value
of
R$
would be:
"R1"
,200,
"R2"
,2200,
"R3"
,10000
This statement
is
useful for reading from a file that consists of lines, not individual
data values, such
as
lines from an ASCII-saved BASIC-80 program file,
or
a docu-
ment created with the
ISIS-II text editor.
The
INPUT$ function reads the specified number
of
characters from a sequential
file:
10
OPEN
"1",#1,":F1:MONTHS"
20
PRINT INPUT$ (3,1)
30
CLOSE
#1
40
END
This program reads the first 3 characters from the file
:Fl
:MONTHS and prints
them.
If
you execute line
20
again, INPUT$
will
read the next 3 characters.
When you read the last value from a file, an end-of-file flag
is
set to
-1.
This flag
can be tested with the
EOF
function.
If
you try to read data from a disk file after the
end-of-file flag
is
set, BASIC-80 issues an INPUT PAST END message and execu-
tion halts.
To
prevent surprises, you can test for an end-of-file with the EOF func-
tion and then branch to an appropriate routine:
250
IF
EOF
(1)
THEN
300
300
CLOSE 1
310
PRINT
"END
OF INPUT
DATA"
Closing a Sequential File
Once you read or write the desired data from or to a sequential file, you must close
the file. This can be done in several ways.
The
CLOSE command closes one
or
more files:
CLOSE 1,2,5
If
you enter CLOSE with no file number, all open files are closed. The END state-
ment and the NEW
and
EXIT
commands close all disk files. After closing a file, you
can open it again for input or output, with the same or a different file number.
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