| 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.
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| Notes |
The Null variable is the Null Variant.
Calculations using nulls yield the EVariantError.
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| Related commands |
| Pointer |
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Defines a general use Pointer to any memory based data |
| Variant |
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A variable type that can hold changing data types |
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| 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;
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| Show full unit code |
4 / 2 = 2
4 / 0 = Invalid
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