EMPTY( ) Function
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