ISNULL( ) Function 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