BOF(), EOF()
She was a phantom of delight
When first she gleamed upon my sight;
William Wordsworth, She Was a Phantom of Delight, 1807
These functions stand for Beginning Of File and End Of File, respectively. They tell you whether the record pointer is at the start or end of a table or cursor.|
Usage |
lReturnValue = BOF( [cAlias | nWorkArea] ) lReturnValue = EOF( [cAlias | nWorkArea] ) |
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Parameter |
Value |
Meaning |
|
cAlias |
Character |
Check the table whose alias is cAlias. |
|
Omitted |
If nWorkArea is also omitted, check the table in the current work area. |
|
|
nWorkArea |
Numeric |
Check the table currently open in nWorkArea. |
|
Omitted |
If cAlias is also omitted, check the table in the current work area. |
|
|
lReturnValue |
.T. |
The specified table is at the beginning or end of file, based on the current order. |
|
.F. |
The specified table is not at the beginning or end of file. |
BOF() and EOF() are not complementary as their names imply.
Instead, we have one of those little inconsistencies that drive
us all nuts. BOF() means at the beginning of the file;
EOF() means beyond the end of the file. BOF() becomes true
when you skip backward from the first record (in the current
order), but the record pointer remains on the first record.
However, every Xbase table has a "phantom" record at the end.
EOF() is true when the record pointer is pointing to the phantom
record, not to the last real record in the table. So the
mechanism for getting to BOF() and EOF() is the same—skip
backward or forward from the first or last record—but the results
are not.
EOF() is useful when a relation has been set between two tables. If you move the record pointer in the parent table, and there are no matching records in the child table, EOF() becomes true for the child table. This is an easy way to check for matching records. Incidentally, you can do the same thing by checking FOUND() in the child area.Besides a lack of relatives, various things can set the record pointer to EOF(). The simplest is to issue SKIP when you're already on the last record. Other things that leave the pointer on EOF() are a SEEK or SEEK() (with SET NEAR OFF) that doesn't find a match, a LOCATE that doesn't locate any matching records, and any of the scoped commands (like REPLACE or COUNT) issued with ALL or REST, and no WHILE clause to stop them sooner.
We recommend strongly that you never use work area numbers as parameters to BOF() and EOF() (or just about any other time, actually). While it's always been better to avoid them, this is even more true in Visual FoxPro, since the visual interface no longer provides a way to choose work areas by number.
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Example |
USE Customer
? RECNO() && 1
? BOF() && .F.
* make BOF() true
SKIP –1
? BOF() && .T.
? RECNO() && Still 1
* now go to the bottom
GO BOTTOM
? EOF() && .F.
? RECNO()
* go to phantom record
SKIP
? EOF() && .T.
? RECNO() && Not the same as above;
&& one more than RECCOUNT()
* check for related records
USE Parent IN 0
USE Child IN 0 ORDER ParentId
SELECT Parent
SET RELATION TO ParentId INTO Child
* Browse child-less parents
BROWSE FOR EOF("Child")
* Another way to do this is:
BROWSE FOR NOT FOUND("Child")
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See Also |