VarIsNull

function VarIsNull(const V: Variant): Boolean;

VarIsNull returns true if the given variant contains the value Null. If the variant contains any other value, the function result is false.

Do not confuse a Null variant with an unassigned variant. A Null variant is still assigned, but has the value Null. Unlike unassigned variants, Null variants can be used in expressions and can be converted to other types of variants.

Example
TRObject Syntax

var
   valueInt : Integer;
   valueFlt : Float;
   valueStr : String;
   valueBool : Boolean;
 
 {
 
  valueInt = nil;
  if (VarIsNull(valueInt))
   ShowMessage('True');
  else
   ShowMessage('False');
   
  if (VarIsNull(valueFlt))
   ShowMessage('True');
  else
   ShowMessage('False');  
  
  if (VarIsNull(valueStr))
   ShowMessage('True');
  else
   ShowMessage('False');
   
  valueBool = true;
  if (VarIsNull(valueBool))
   ShowMessage('True');
  else
   ShowMessage('False');
 
 }

Base Syntax

var
  valueInt : Integer;
  valueFlt : Float;
  valueStr : String;
  valueBool : Boolean;

begin

 valueInt := nil;
 if VarIsNull(valueInt) then
  ShowMessage('True');
 else
  ShowMessage('False');
  
 if VarIsNull(valueFlt) then
  ShowMessage('True');
 else
  ShowMessage('False');  
 
 if VarIsNull(valueStr) then
  ShowMessage('True');
 else
  ShowMessage('False');
  
 valueBool := true;
 if VarIsNull(valueBool) then
  ShowMessage('True');
 else
  ShowMessage('False');

end;

Output:

False
True
True
False

See Also

• Boolean Functions