Intel 9800758-02 manual Opening a Sequential File, Open 1,#1,F1DATES

CHAPTER 5

DISK FILE INPUT/OUTPUT

BASIC-SO includes two types of disk file Input/Output operations: sequential and random. Sequential I/O lets you read or write a file from the beginning to the end; random I/O lets you specify where in the file you read or write.

Because BASIC-SO runs under ISIS-II and RMX/SO, filenames correspond to the ISIS-II and RMX/80-DFS format (:Fn:name.ext, where n is the drive number). BASIC-SO also gives you access to disk file-handling commands:

•DIR, which lists the files on a disk

•RENAME, which changes the name of a disk file

•ATTRIB, which changes the attributes of a disk file

•KILL, which deletes a disk file (it is actually the system DELETE command, but the name must be different because BASIC-SO includes a DELETE command to delete lines from a program).

For more information about ISIS-II filenames or operations, see the ISIS-II User's

Guide.

Although both sequential and random I/O allow you to create, read, and write files on disk, sequential I/O is somewhat simpler in concepts and operation. If you haven't worked with disk files before, it would probably be better to start with se- quential 110 to learn the principles.

Sequential File 1/0

BASIC-SO Sequential I/O allows you to build sequential data files containing numbers and strings of up to 255 characters. In general, to use sequential 110 you must open the file, execute a series of INPUT (to read) or PRINT (to write) statements, then close the file.

A sequential file is open either for input or output. To switch from one to the other, you must close the file and open it again with the opposite attribute. Any 110 opera- tion that immediately follows an OPEN statement starts at the beginning of the file.

Opening a Sequential File

You open a sequential file with the OPEN statement. It specifies whether the file is to be opened for input or output, assigns it a file number, and specifies the filename. Up to six files can be open at one time. If the file named in an OPEN statement that specifies output does not exist, it is created. Once a file is open, it cannot be opened again without closing it first. If you attempt to do so, an error message results.

To open an input file named :Fl:DATES and assign it file number 1:

OPEN "1",#1,":F1:DATES"

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