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BOF()
Determine when beginning of file is encountered
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Syntax
BOF() --> lBoundary
Returns
BOF() returns true (.T.) after an attempt to SKIP backward beyond the
first logical record in a database file; otherwise, it returns false
(.F.). If there is no database file open in the current work area,
BOF() returns false (.F.). If the current database file contains no
records, BOF() returns true (.T.).
Description
BOF() is a database function used to test for a boundary condition when
you are moving the record pointer backward through a database file using
the SKIP command. A simple usage example is a descending order record
list with an ascending order index file. A more sophisticated example
is a screen paging routine that pages forward or backward through the
current database file based on the key the user presses. When the user
attempts to page backward, you would use BOF() to test for a beginning
of file condition before using the SKIP command to move the record
pointer and repaint the screen.
Once BOF() is set to true (.T.), it retains its value until there is
another attempt to move the record pointer.
By default, BOF() operates on the currently selected work area. It can
be made to operate on an unselected work area by specifying it within an
aliased expression (see example below).
The SKIP command is the only record movement command that can set BOF()
to true (.T.).
Examples
. This example demonstrates BOF() by attempting to move the
record pointer before the first record:
USE Sales NEW
? RECNO(), BOF() // Result: 1 .F.
SKIP -1
? RECNO(), BOF() // Result: 1 .T.
. This example uses aliased expressions to query the value of
BOF() in unselected work areas:
USE Sales NEW
USE Customer NEW
USE Invoices NEW
? Sales->(BOF()), Customer->(BOF())
Files Library is CLIPPER.LIB.
See Also:
EOF()
SKIP
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