Delphi Basics : $IfDef command

DelphiBasics

$IfDef
Compiler Directive

Executes code if a conditional symbol has been defined

{$IfDef Symbol}
... Code to run when the symbol is defined ...
{$Else}
... Code to run when the symbol is not defined ...
{$EndIf}

Description

The $IfDef compiler directive starts a section of conditionally compiled code. Only if the specified Symbol has been defined.

Symbols come in two types. Predefined in Delphi, such as Console when running a console application. And defined by the $Define compiler direcctive.

$IfDef is very useful when developing code, allowing various sections to be compiled when testing.

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
$IfNDef		Executes code if a conditional symbol has not been defined
$IfOpt		Tests for the state of a Compiler directive
$UnDef		Undefines a compiler directive symbol - as used by IfDef

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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}

  // Display the value of text if we are in test mode
  {$IfDef TESTMODE}
  ShowMessage('text = '+text);
  {$Else}
  ShowMessage('Out of test mode now');
  {$EndIf}
end;

Show full unit code

We are in test mode
Out of test mode now