Commodore Plus 4 - Page 375

The Datassette Tape Recorder 363
The VERIFY command is also useful when you want to position the tape
beyond the last file recorded on it. After you rewind the tape, request a VERIFY
of the last file on the tape. Of course, a VERIFY ERROR is reported (unless the
last file is identical to the program in memory). But the tape is positioned just
after the file, ready for a new file to be recorded.
Using Data Files A data file on tape consists of a long series of bytes stored on
the tape. It can be identified with a name and is concluded with an end-of-file (or
end-of-tape) mark. The purpose for which the file is being accessed must be given
in the secondary address sent with the OPEN statement:
OPEN filenumber,1, secondary,filename
The filenumber is the logical file number to be associated with this file. It is for
reference purposes only and can be 0-127 (128-255 will send a linefeed character
following every carriage return). The secondary address specifies the use of the
file. If it is 0 (or omitted), the file is read. If it is 1, the file is written and ended with
an end-of-file. If it is 2, the file is written and ended with an end-of-tape. The last
parameter is the file name (a string expression up to 17 characters).
After the file is open, output may be directed to it by referring to its logical file
number in a PRINT# or CMD command. Input may be received from it by
referring to its logical file number in a INPUT# or GET# command.
When the input to or output from a file is complete, the file must be closed with
CLOSE filenumber
where filenumber is the logical file number of the file to close.
After a file is opened for writing, each byte that is sent to it is stored sequen
tially on the tape. The format of the bytes written to a tape file must be designed
with the method of retrieval in mind. If they are to be read one at a time using the
GET# command, any format is all right. However, if they are to be read using the
INPUT# command, care must be taken to store comma characters between
values and carriage return characters between lines of input.
Example: 10 G0SUB130
SO OPEN"l,l,l,"nATFIL"
30 PRIlTTCHR$(13)//WHATT0ST0RE//;:I]SrPUTA$
40 PRI1TT#1,A$
SO CLOSE1
60 G0SUB130
70 PJEtINT"REWIlTD THE TAPE":WAIT64784,4,4
80 PRHSTT^WHEU D01TE, ";:G0SUB130
90 0PEITl,l,0,"DATFIL"