Commodore Plus 4 - Page 340

328 Using Peripheral Devices
Program Files
The program file type is used for storage of programs. It can also be used for data
storage and is opened with a file type parameter of P. Its format is identical to the
sequential file format. When a program file is created by a save command, the
first 2 bytes of the file contain the address from which the program was saved. The
following example illustrates this. Type in the program and save it with the
following command:
DSAVE'TROGRAM"
Then run the program. It reads in the load address that was saved in the file and
prints it out.
Example: 10 0PENl,8,2,"PR0GRAM"
20 IPDS<>OTHEITPRI]SrTDS$:CLOSEl:E]SrD
30 GET#lrAL$:GET#lrAH$
40 A=ASC(AH$)*256+ASC(AL$)
50 PRI^'THE LOAD ADDRESS IS ";A
60 CLOSE1
Line-by-Line Explanation
10 Open the program file with read access (the default).
20 Check for errors. If there is an error, quit.
30 Get the first 2 bytes in the file.
40 Calculate the load address.
50 Output the load address.
60 Close the file.
Relative Files
The types of files discussed previously store information sequentially; that is, to
read a single item somewhere in the middle of the file, you must first read all the
items before it. To reread the item, you must start at the beginning again. When
data will be accessed in a "random" fashion (i.e., you are equally likely to want to
access any piece of data), a relative file can be used.
A relative file is opened with a file-type parameter of L. A relative file is a series
of "records." Each record contains the data for one individual in the database and
is of a predetermined length. When you create a relative file, the record length
must be specified. The syntax is