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18 Sep 1987 get/put element routines
The user-callable get/put element routines are tbegt[tbird] and
tbept[tbird]. In outline, each of these routines calls tbeoff to get
the offset to the element (i.e. row & column) to be gotten or put,
then calls a get/put primitive routine (tbegp[], tbepp[]) of the data
type of the column, and finally converts the data type if that is
necessary. If the data type of the column is the same as that of the
I/O buffer then the value is read directly into or from that buffer.
No separate null flag is returned by tbegt[]; if the table value is
undefined the output value will be INDEF.
A subroutine call could have been saved by writing tbeoff into
each of the get/put primitives. That would have been very reasonable,
but there were a couple of reasons for not doing it that way. I would
like to replace the seek & read or seek & write in get/put row (tbrgt[],
tbrpt[]) by calls to these get/put primitives, and in that case the
offset does not need to be recomputed from scratch for each column.
If we ever have 3-D tables (i.e. entries which are arrays) then these
primitives could still be used for getting/putting single elements in
the arrays.
I should also write get/put array primitives for get/put column
or for arrays in 3-D tables. Eventually it would be nice to include
conversion between machine-dependent and machine-independent formats
in these primitives.
The use of TB_CURROW and TB_OFFSET in tbrgt[] and tbrpt[] seems
rather clumsy. I think it would be better to just call tbxoff or tbeoff.
1 Oct 1987 tbpset & tbpsta for FIO buffer size
I have not handled this very well. It is supposed to be not possible
to set the FIO buffer size after the first I/O operation to a file. When
an existing table is opened by tbtopn, the size-information record is read.
For a new table tbtopn does not actually call open (but perhaps it should!),
so the buffer size can't be set before calling tbtcre, which does call open
but which also writes the size-info record to the table. So in neither case
is it possible to change the FIO buffer size. My solution, in the routine
tbtfst, was to close the table file (using close, not tbtclo), reopen it,
and then call fset before any I/O operation is done. This precludes calling
tbpset to set the buffer size (e.g. advice=RANDOM) for a new table between
calls to tbtopn and tbtcre. This is just where you would expect to be able
to set it, however, so one of these days I will have to make that possible.
This could be done by calling open in tbtopn even for a new table but not
writing to the table until the call to tbtcre.
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