Note
Access to this page requires authorization. You can try signing in or changing directories.
Access to this page requires authorization. You can try changing directories.
Determines whether an expression evaluates to empty.
EMPTY(eExpression)
Parameters
- eExpression
Specifies the expression that EMPTY( ) evaluates. You can specify an expression with Character, Numeric, Date, Varbinary, Blob, or Logical type, or the name of a Memo or General field in an open table.
Return Value
Logical. EMPTY( ) returns True (.T.) if the expression eExpression evaluates to empty; otherwise, EMPTY( ) returns False (.F.).
When expression types evaluate to the values in the following table, EMPTY( ) returns True (.T.).
Expression type |
Evaluates to |
|---|---|
Blob |
Empty (0h) or contains only zero bytes, for example, 0h00, 0h000000, and so on |
Character |
Empty string, spaces, tabs, carriage returns, linefeeds, or any combination of these |
Currency |
0 |
Date |
Empty, for example, CTOD('') |
DateTime |
Empty, for example, CTOT('') |
Double |
0 |
Float |
0 |
General |
Empty (no OLE object) |
Integer |
0 |
Logical |
False (.F.) |
Memo |
Empty (no contents) |
Numeric |
0 |
Varbinary |
Empty (0h) or contains only zero bytes, for example, 0h00, 0h000000, and so on |
Remarks
You cannot use EMPTY( ) to determine whether a variable object reference is empty. For example, a variable can contain an object reference for a form. If the form is closed by clicking Close from the form's pop-up menu or by issuing CLEAR WINDOWS, the variable contains the null value.
The following program example demonstrates how to use TYPE( ) and ISNULL( ) to determine if a variable object reference is valid.
goMyForm = CREATEOBJECT('Form')
WAIT WINDOW IIF(TYPE('goMyForm') = 'O' AND !ISNULL(goMyForm), ;
'goMyForm has valid object reference',;
'goMyForm does not have valid object reference')
Example
The following example opens the customer table in the testdata database. FOR ... ENDFOR is used to create a loop in which EMPTY( ) s used to determine if TAG( ) returns the empty string. The name of each structural index tag is displayed with its candidate status.
CLOSE DATABASES
OPEN DATABASE (HOME(2) + 'data\testdata')
USE customer && Open customer table
FOR nCount = 1 TO TAGCOUNT( )
IF !EMPTY(TAG(nCount)) && Checks for empty string
? TAG(nCount) && Display tag name
? CANDIDATE(nCount) && Display candidate status
ELSE
EXIT && Exit the loop when no more tags are found
ENDIF
ENDFOR