Suggestions for FIlEMAN.E
Suggestions for Fileman.e
Like Dbase, how about a status byte as the first character in a record?
To represent a deleted record, place an ASCII 0 there, and an ASCII 1 or
larger code to represent a valid, active record. Thus, when you
delete a record, all you need to do is set the status byte to zero. You
can leave the actual record data alone, which will permit an undelete
later, if you desire.
One record format I read about placed an ASCII 26 after the header
identification. ASCII 26 is the old end of file marker for DOS.
Thus, if you placed such a character at byte position
3, then if the file is read in line mode, by Euphoria or another program,
all they will see is Eu.
I think Ralf mentioned that you should open these files in binary mode.
That way any character from 0 to 255 is permissable and will not affect
the read or write routines.
You will need to have a way to sort the file records. I would think
sorting by some combination of fields would be a nice touch. If you
include the status byte, then you could sort all deleted records to
the end of the file, or simply drop them.
If an area in the header were to be reserved as a pointer to the
first deleted record, you would be able to add a record by reusing
the space occupied by a deleted record. And if that record were big
enough, it could in turn point to the next deleted record.
It might be fun to code a routine to compact the file in place.
That is, you could rearrange the file such that all deleted records
are placed after all the data records, without coping to a second file.
Indexing comes to mind, also.
Larry Gregg
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