////// 2031 User's Manual - Part 2 \\\\\\\



					Chapter 6

					ADVANCED

						FILE

					MANAGEMENT

In the preceding chapters, you learned how to manipulate files on the disk, and
were shown the format of commands used to create and update files. In this
chapter, you will utilize these skills in a file handling application using random
or relative access.

	SPECIAL OPEN AND CLOSE STATEMENTS
				FOR DIRECT ACCESS

The BASIC statements (after initializing the disk):

	OPEN2,8,4,"#"

and

	OPEN2,8,4,"#0"

are examples that show how to open a channel to one buffer (to be used with the
block commands). In the first example, the first available buffer is allocated to
channel 4. The second example is an attempt to allocate buffer 0 to the channel.

											55


If the buffers are not available, a NO CHANNEL error condition is generated.
The explicit buffer allocation can be used to reserve a buffer for position
dependent code as in the case of a EXECUTE command.

Execute a GET# statement to find the number of the allocated buffer. The byte
transmitted is the buffer number. A buffer number may only be obtained
PRIOR TO any write or read operations to that buffer.

The CLOSE statement clears the OPENed channel and writes the BAM to the
diskette that was last used by that channel. To avoid confusion, limit yourself to
accessing one drive with any direct access channel.

RANDOM ACCESS EXAMPLE

Since the BLOCK-ALLOCATE command returns the next available diskette
block through the error channel, it can be used in the allocation of records. This
feature allows creating a random file without being concerned with the actual
physical structure of the diskette. However, the allocated blocks must first be
recorded in a sequential or user file in order to be referenced by the BASIC
program.

The following random file example demonstrates the use of block access com-
mands. Notice that the U1 and U2 commands are used. These commands are
used since more than one record is stored in a block and it is necessary to
manage end-of-record pointers in BASIC. A smaller application might take
advantage of the B-R and B-W commands.

Chapter 9 contains a complete listing of the random access program entitled
"RANDOMEXAMPLE". The example program is built upon a relative record
scheme and provides single record access through BASIC programming. Most
of the programming below line 20000 is relative record access. The field accessing
routines left-justify binary and alpha fields, and right-justify numeric fields.

In an actual situation, the program should generate error messages to the opera-
tor, or automatically take corrective action such as rounding numbers to fit a
field. It would also be possible to add data sorts and searches as well as key
fields to the program. Record size, including field markers, must be less than 254
characters. Field size is restricted to 80 characters because of the restrictions of
the BASIC INPUT# statement. Longer fields could be used if the BASIC pro-
gram were modified to use GET# for retrieval but that procedure would be much
slower.

								56

Two sequential files are used to support the random access file in this example.
Each file bears the name of the file name given in the CREATE file code (lines
1100 to 1180) plus a six-character extension. Since primary file names are ten or
less characters, the file names are padded with spaces. The two files are named
FILENAME   .DESCR and FILENAME   .KEY01.

The descriptor (    .DESC) contains information about record structure and
location. The primary key file (     .KEY01) contains the first field of each record
and the relative record number. This example allows the random records to
reside on a separate diskette from the sequential support files, thereby providing
added room for random data. The OPEN code (lines 1200 to 1275) requires the
disk ID of the random file disk for comparison.

NOTE

The DOS Support Program must not be in the computer
when running this program.

				To Create A File:

STEP 1.	Insert the Demo Disk.

STEP 2.	Type:  LOAD"RANDOM*",8 and press RETURN

	This loads the Random Program

STEP 3.	Type:  OPEN 15,8,15 and press RETURN

	This opens the command channel.

STEP 4.	Remove the Demo Disk and insert a blank disk.

STEP 5.	Type:  PRINT#15,"NO:MAILING LIST,CS" and press RETURN

STEP 6.	Type:  RUN and press RETURN

	The screen diskplays: "DO YOU WISH TO CREATE A FILE"?

STEP 7.	Type:  Y and press RETURN

	The screen displays: "RANDOM FILE NAME"?

STEP 8.	Type the file name: PHONE LIST and press RETURN

	The screen displays: "KEY FILE DRIVE NUMBER"?

STEP 9.	Type:  0 and press RETURN

	The screen displays: "RANDOM FILE NUMBER"?

							57