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dos #19
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2022-08-26
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DOS and DON'Ts -- Part 19
by Joel Ellis Rea
The format of an OPEN statement for
APPEND is:
OPEN <filenum>, <unitnum>, <chan-
nelnum>, '<filename>,[<type>]
,A[PPEND]'
Some examples:
OPEN 8, 8, 8, "DATAFILE,A"
OPEN F%, U%, C%, F$ + ",S,A"
OPEN 1, 8, 2, "1:MACHLANG,P,A"
The first example OPENs the file
DATAFILE as file #8 via channel #8 of
drive unit #8. The file type is not
checked, and the OPEN succeeds if the
file exists and is of type SEQ, PRG
or USR (REL and DEL don't work with
,A[PPEND], of course). If the OPEN
succeeds, all further PRINT#8 state-
ments will write their data starting
at the END of DATAFILE.
The second example OPENs a file
whose name is in the string variable
F$, giving it the file reference num-
ber specified in the integer variable
F%, via the channel in C% on the unit
in U%. Since the file type was speci-
fied, the OPEN fails if the file is
not found, or if it is found but is
not of type SEQ.
The third example OPENs file 'MACH-
LANG', which must exist on drive 1 (of
a two-unit drive such as a CBM 4040 or
an MSD SD-2) as a PRG file. This
might be used to add bytes to binary
data such as a translation table.
It is important to note that the ,A
mode REQUIRES that the file ALREADY
EXISTS on the disk. So before you can
use the ,A mode on a new file, you
must first create the file with the
OPEN statement with a ,W parameter,
followed by at least one PRINT# state-
ment, followed by a CLOSE statement.
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