ISNULL( ) Function
Returns true (.T.) if an expression evaluates to a null value; otherwise, ISNULL( ) returns false (.F.).
ISNULL(eExpression)
Return Values
Logical
Parameters
- eExpression
Specifies the expression to evaluate.
Remarks
Use ISNULL( ) to determine if the contents of a field, memory variable, or array element contains a null value, or if an expression evaluates to a null value.
Example
In the following example, ISNULL( ) is used to check for a null value.
STORE .NULL. TO mNullvalue && Store a null value to a memory variable
CLEAR
? mNullvalue && Display the value of the memory variable
? ISNULL(mNullvalue) && Returns .T., indicating a null value
? TYPE('mNullvalue') && Returns L, indicating a logical value
? (mNullvalue = .NULL.) && Returns .NULL., bad test for null values