Guardian Procedure Calls Reference Manual (G06.25+)

Guardian Procedure Calls (H-K)
Guardian Procedure Calls Reference Manual—522629-013
7-60
KEYPOSITION[X] Procedures
(Superseded by FILE_SETKEY_ Procedure)
When positioning by standard (not insertion-ordered) alternate key, you can save
the current file position for later access by concatenating alternate-key value and
primary key values in a temporary buffer. This permits you to return to that position
in a key-sequenced file; for example:
temporary-buffer ':='
record.altkeyfield FOR $LEN (record.altkeyfield)
& record.primarykey FOR $LEN (record.primarykey);
Use the following to reposition to the same record:
KEYPOSITION ( filenum , temporary-buffer
, key-specifier ,
$LEN (record.altkeyfield) +
$LEN (record.primarykey) ,
positioning-mode );
Use the following to reposition to the next record:
KEYPOSITION ( filenum , temporary-buffer ,
key-specifier ,
$LEN (record.altkeyfield) +
$LEN (record.primarykey),
%100000 + positioning-mode );
In either case, if generic positioning is desired, the generic length would be placed
in the upper 8 bits of the
length-word parameter.
This method will not work when positioning with an insertion-ordered alternate key,
because the value of the timestamp portion of the alternate key is not contained in
the primary record. However, you can use the SAVEPOSITION and REPOSITION
procedures to save and restore the current position when positioning to an
insertion-ordered alternate (or any other) key is in effect.
•
Positioning to the start of a file
To position to the first record of a key-sequenced file, you can use the following call
to specify a zero
length-word:
INT ZERO := 0;
CALL KEYPOSITION ( FILENUM , ZERO ,, ZERO );
•
Considerations for Position-to-Last Option
The standard operation of KEYPOSITION is to position to the first record that
satisfies the positioning criteria specified by
key-value, key-length, compare-
length, and positioning-mode. When reading a file in reverse order,
however, you might want to position to the last record in the set of records
matching the positioning criteria. Consider the following records:
Record Number Key Value
0AAA
1ABA