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Returns true (.T.) if an expression evaluates to a null value; otherwise, ISNULL(В ) returns false (.F.).

ISNULL(eExpression)

Parameters

eExpression


Specifies the expression to evaluate.

Return Value

Logical

Remarks

Use ISNULL(В ) 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(В ) is used to check for a null value.

В Copy Code
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

See Also



JavaScript Editor js editor     Web development