| Description |
The $UnDef compiler directive removes a Symbol definition. By doing so, the symbol is now Off.
When a symbol is on, $IfDef will compile conditional code, and $IfNDef will not.
When a symbol is off, $IfNDef will compile conditional code, and $IfDef will not.
Delphi provides some predefined symbols, such as Console that is on for a console application and off for a GUI application.
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| Related commands |
| $Define |
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Defines a compiler directive symbol - as used by IfDef |
| $Else |
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Starts the alternate section of an IfDef or IfNDef |
| $EndIf |
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Terminates conditional code compilation |
| $IfDef |
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Executes code if a conditional symbol has been defined |
| $IfNDef |
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Executes code if a conditional symbol has not been defined |
| $IfOpt |
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Tests for the state of a Compiler directive |
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| Example code : Setting up and using a test mode symbol |
// Full Unit code.
// -----------------------------------------------------------
// You must store this code in a unit called Unit1 with a form
// called Form1 that has an OnCreate event called FormCreate.
unit Unit1;
interface
uses
Forms, Dialogs;
type
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
end;
var
Form1: TForm1;
implementation
{$R *.dfm} // Include form definitions
procedure TForm1.FormCreate(Sender: TObject);
var
text : string;
begin
// Set our code into test mode
{$Define TESTMODE}
text := 'We are in test mode';
// Display the value of text if we are in test mode
{$IfDef TESTMODE}
ShowMessage('text = '+text);
{$EndIf}
// Switch off test mode
{$UnDef TESTMODE}
text := 'We are out of test mode';
// Display the value of text if we are in test mode
{$IfDef TESTMODE}
ShowMessage('text = '+text);
{$EndIf}
end;
end.
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| Hide full unit code |
text = We are in test mode
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