var Null : Variant;
Description
The Null variable has an undefined value.
Null does not mean a zero number or empty string - it is undefined. Any expression using a null variable will yield a null result.
Null is particularly useful when handling SQL table data - providing a one for one correspondence with the SQL NULL value.
Notes
The Null variable is the Null Variant.
Calculations using nulls yield the EVariantError.
Related commands
Pointer Defines a general use Pointer to any memory based data
Variant A variable type that can hold changing data types
Example code : Using Null to represent the result of a bad divide
var
Answer : Variant;
begin
Answer := Divide(4,2);
// Show the result of this division
if Answer = Null
then ShowMessage('4 / 2 = Invalid')
else ShowMessage('4 / 2 = '+IntToStr(Answer));
Answer := Divide(4,0);
// Show the result of this division
if Answer = Null
then ShowMessage('4 / 0 = Invalid')
else ShowMessage('4 / 0 = '+IntToStr(Answer));
end;
function TForm1.Divide(Dividend, Divisor: Integer) : Variant;
begin
// Try to divide the Dividend by the Divisor
try
Result := Dividend div Divisor;
except
Result := Null ; // Assign Null if the division threw an error
end;
end;
Show full unit code
4 / 2 = 2
4 / 0 = Invalid