Mega Code Archive
$undef - undefines a compiler directive symbol - as used by ifdef
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{$UnDef Symbol}
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.
Related commands
$Define Defines a compiler directive symbol - as used by IfDef
$Else Starts the alternate section of an IfDef or IfNDef
$EndIf Terminates conditional code compilation
$IfDef Executes code if a conditional symbol has been defined
$IfNDef Executes code if a conditional symbol has not been defined
$IfOpt Tests for the state of a Compiler directive
Example code : Setting up and using a test mode symbol
var
text : string;
begin
// Set our code into test mode
{$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;
Show full unit code
text = We are in test mode
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