Direct Accessing With The Notelpointcommands - Atari DOS 2.5: XF551 Owner's Manual

PRINT performs what is called record
1/0.
Records are sets of
bytes separated by end-at-line characters (98 Hex). The size of a
record is arbitrary. Record size can be determined by the length
of a string printed to a diskette file or the format of an arithmetic
variable. It can also be the length of a string of characters en-
tered from the keyboard and terminated by I
Retirn J.
The INPUT statement cannot generally read a record that is
longer than 255 characters in length . If you PRINT a record to the
disk that you might later want to INPUT, it is best to limit the size
of the PAINTed records to 255 characters or less.
Direct Accessing With the
NOTE/POINT Commands
NOTE (NO.)
Format: NOTE #iocb, avar, avar
Example: tmTE # 2, A, B
Files are created sequentially and are normally accessed from
beginning to end.
If
you want to access the records in a file in a
nonsequential manner (directly), you can either read the file
sequentially and stop at the record you want , or use a special
method of addressing the record you want.
Because the former is very time-consuming for large files, DOS
2.5 incorporates NOTE and POINT to give you the capability of
accessing a file randomly. To get to a record without going
through every record that precedes it, you need to let the com-
puler know what record you want. This requires a "note" of the
file 's sector, so you use a NOTE command before each write and
save the returned value in a table.
This command gets the value of the current file pointer for the file
using the specified 10GB. The file pointer specifies the exact
position in the file where the next byte is to be read or written.
This command stores the absolute disk sector number in the first
arithmetic variable and the current byte number in the second .
Sector numbers range from
1
to 719 in single density and 1 to
1023 in enhanced density; byte numbers range from 0 to 124.
70