Conditional compilation (Delphi)

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Conditional compilation is based on the existence and evaluation of constants, the status of compiler switches, and the definition of conditional symbols.

Conditional symbols work like Boolean variables: they are either defined (True) or undefined (False). Any valid conditional symbol is treated as false until it has been defined.

You can define a conditional in the following ways:

  • Use the {$DEFINE} directive to set a specified symbol to True, and the {$UNDEF} directive to set the symbol to False.
  • Use the -D switch with the command-line compiler (this option is supported by all the Delphi compilers).
  • Add the symbol to the Conditional Defines field on the Project > Options > Delphi Compiler page.

The conditional directives {$IFDEF}, {$IFNDEF}, {$IF}, {$ELSEIF}, {$ELSE}, {$ENDIF}, and {$IFEND} allow you to compile or suppress code based on the status of a conditional symbol. {$IF} and {$ELSEIF} allow you to base conditional compilation on declared Delphi identifiers. {$IFOPT} compiles or suppresses code depending on whether a specified compiler switch is enabled.

For example, the following Delphi code snippet processes differently depending on whether the DEBUG conditional define is set ({$DEFINE DEBUG}): 

  {$DEFINE DEBUG}
    {$IFDEF DEBUG}
    Writeln('Debug is on.');  // This code executes.
    {$ELSE}
    Writeln('Debug is off.');  // This code does not execute.
    {$ENDIF}
    {$UNDEF DEBUG}
    {$IFNDEF DEBUG}
    Writeln('Debug is off.');  // This code executes.
    {$ENDIF}
Note: Conditional symbols are not Delphi identifiers and cannot be referenced in actual program code. Similarly, Delphi identifiers cannot be referenced in any conditional directives other than {$IF} and {$ELSEIF}.
Note: Conditional definitions are evaluated only when source code is recompiled. If you change a conditional symbol status and then rebuild a project, source code in unchanged units may not be recompiled. Use Project > Build All Projects to ensure that everything in your project reflects the current status of conditional symbols.
Note: If you modify the name of a conditional define in the Project > Options > Delphi Compiler, you need to Build your project (Project > Build <ProjectName> or Shift + F9) for the changes to take effect.

Conditional-directive constructions can be nested up to 32 levels deep. For every {$IFxxx}, the corresponding {$ENDIF} or {$IFEND} must be found within the same source file. Conditional symbols must start with a letter, followed by any combination of letters, digits, and underscores; they can be of any length, but only the first 255 characters are significant.

Predefined Conditionals

The following standard conditional symbols are defined:

Category Symbol DCC32 DCC64
Since XE2 		DCCOSX64
Since 10.3 Rio Release 2 		DCCAARM
In XE5 		DCCIOSARM64
Since XE8 		DCCLINUX64
Since 10.2 Tokyo 		DCCAARM64
Since 10.3 Rio Release 3 		DCCOSXARM64
Since 11.0 Alexandria Release 		DCCIOSSIMARM64
Since 11.2 Alexandria Release 		Comments
Compiler DCC DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED
VER340
For a list of compiler versions, see Compiler Versions.		 DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED For Delphi Sydney, compiler version 34.0 has VER340 defined.
Platform CONSOLE DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED Defined if an application is being compiled as a console application.
IOS not defined not defined not defined N/A DEFINED not defined not defined not defined DEFINED Defined if the target platform is iOS.
*New* in XE4/iOS.
IOS64 not defined not defined not defined not defined DEFINED not defined not defined not defined DEFINED Defined if the target platform is iOS64.
Since XE8/iOSarm64.
OSX not defined not defined DEFINED not defined not defined not defined not defined DEFINED not defined Defined if the target platform is macOS.
*New* in XE2/macOS.
OSX64 not defined not defined DEFINED not defined not defined not defined not defined DEFINED not defined Defined if the target platform is macOS.
*New* in 10.3.2 .
NATIVECODE DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED Since Delphi.Net
MSWINDOWS DEFINED DEFINED not defined not defined not defined not defined not defined not defined not defined Indicates that the operating environment is Windows. Use MSWINDOWS to test for any flavor of the Windows platform instead of WIN32.
WIN32 DEFINED not defined not defined not defined not defined not defined not defined not defined not defined Target platform is the native 32-bit Windows platform.
WIN64 not defined DEFINED not defined not defined not defined not defined not defined not defined not defined Target platform is 64-bit Windows.
*New* in XE2/x64.
MACOS not defined not defined DEFINED not defined DEFINED not defined not defined DEFINED DEFINED Target platform is an Apple Darwin OS (macOS or iOS).
Note: This symbol existed before Apple changed the name of OS X to macOS.
*New* in XE2/macOS.
MACOS32 not defined not defined not defined not defined not defined not defined not defined not defined not defined Target platform is 32-bit Apple Darwin OS (32-bit macOS or 32-bit iOS).
Note: This symbol existed before Apple changed the name of OS X to macOS.
*New* in XE2/macOS.
MACOS64 not defined not defined DEFINED not defined DEFINED not defined not defined DEFINED DEFINED Target platform is 64-bit Apple Darwin OS (64-bit macOS or 64-bit iOS).
Note: This symbol existed before Apple changed the name of OS X to macOS.
*New* in XE8/macOS.
LINUX not defined not defined not defined not defined not defined DEFINED not defined not defined not defined Since Kylix.
LINUX32 not defined not defined not defined not defined not defined not defined not defined not defined not defined Since Kylix.
LINUX64 not defined not defined not defined not defined not defined DEFINED not defined not defined not defined New in 10.2
POSIX not defined not defined DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED Since Kylix.
POSIX32 not defined not defined not defined DEFINED DEFINED not defined not defined not defined not defined Since Kylix.
POSIX64 not defined not defined DEFINED not defined DEFINED DEFINED DEFINED DEFINED DEFINED Since Kylix.
ANDROID not defined not defined not defined DEFINED not defined not defined DEFINED not defined not defined Defined if the target platform is Android.
*New* in XE5.
ANDROID32 not defined not defined not defined DEFINED not defined not defined not defined not defined not defined Since XE8/iOSarm64.
ANDROID64 not defined not defined not defined not defined not defined not defined DEFINED not defined not defined Delphi compiler for Android 64-bit platform.
*New* in 10.3.3.
CPU CPU386 DEFINED not defined DEFINED not defined not defined note defined not defined not defined not defined Indicates that the CPU is an Intel 386 or later.
CPUX86 DEFINED not defined not defined not defined not defined not defined not defined not defined not defined CPU is an Intel 386 or later on any platform.
*New* in XE2/x64.
CPUX64 not defined DEFINED DEFINED not defined not defined DEFINED not defined not defined not defined The CPU supports the x86-64 instruction set, and is in a 64-bit environment.
*New* in XE2/x64.
CPU32BITS DEFINED not defined not defined DEFINED not defined not defined not defined not defined not defined The CPU is in a 32-bit environment, such as DCC32.EXE.
*New* in XE8.
CPU64BITS not defined DEFINED DEFINED not defined DEFINED DEFINED DEFINED DEFINED DEFINED The CPU is in a 64-bit environment, such as DCC64.EXE.
*New* in XE8.
CPUARM not defined not defined not defined DEFINED DEFINED not defined DEFINED DEFINED DEFINED Defined if the CPU is based on the ARM architecture..
*New* in XE4/iOS.
CPUARM32 not defined not defined not defined DEFINED not defined not defined not defined not defined not defined The CPU is in a 32-bit ARM environment.
*New* in XE8.
CPUARM64 not defined not defined not defined not defined DEFINED not defined DEFINED DEFINED DEFINED The CPU is in a 64-bit ARM environment, such as DCCIOSARM64.EXE.
*New* in XE8.
Availability ALIGN_STACK not defined not defined not defined not defined not defined not defined not defined not defined not defined Defined in code that may be shared with the macOS compiler and another compiler on another platform such as Linux that does not have a rigid stack alignment requirement. For more information, see Eli Boling's blog at http://blogs.embarcadero.com/eboling/2009/05/20/5607 .
*New* in XE2/macOS.
ASSEMBLER DEFINED DEFINED not defined not defined not defined not defined not defined not defined not defined Assembler syntax is accepted.
AUTOREFCOUNT (*) not defined not defined DEFINED DEFINED DEFINED not defined DEFINED if 10.2.
Not defined since 10.3.		 not defined not defined Defined for compilers that use automatic reference counting, such as the Delphi mobile compilers.
*New* in XE4/iOS. Removed in 10.4 Sydney.
EXTERNALLINKER not defined not defined DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED Defined for compilers that have an external linker and the LLVM code generator; the Delphi mobile compilers have the external ld linker and use LLVM as code generator.
*New* in XE4/iOS.
UNICODE DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED UNICODE is defined as the default string type.
CONDITIONALEXPRESSIONS DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED Tests for the use of the $IF directive.
ELF not defined not defined not defined not defined not defined DEFINED not defined not defined not defined Defined when targeting Executable and Linkable Format (ELF) files.
NEXTGEN (*) not defined not defined DEFINED DEFINED DEFINED DEFINED if 10.2.
Not defined since 10.3.		 not defined not defined not defined Defined for compilers (such as the Delphi mobile compilers) that use "next-generation" language features, such as 0-based strings.
*New* in XE4/iOS. Removed in 10.4 Sydney.
PC_MAPPED_EXCEPTIONS not defined not defined not defined not defined not defined not defined not defined not defined not defined Defined when compiling on a platform or for a target platform that uses address maps instead of stack frames to unwind exceptions (such as macOS).
*New* in XE2.
PIC never never always DEFINED always DEFINED always DEFINED always DEFINED always DEFINED always DEFINED always DEFINED Defined for platforms that require Position-Independent Code (PIC), such as macOS.
UNDERSCOREIMPORTNAME DEFINED not defined not defined not defined not defined not defined not defined not defined not defined Defined for compilers that add a leading underscore (for example, in names of dynamic libraries imported from Mac OS).
*New* in XE4/iOS.
WEAKREF DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED Defined for compilers that can use weak references (the [weak] attribute).
*New* in XE4/iOS.
WEAKINSTREF (*) DEFINED DEFINED not defined not defined not defined DEFINED not defined DEFINED DEFINED Defined when weak references are defined for instances.
*New* in XE4/iOS. Removed in 10.4 Sydney.
WEAKINTFREF DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED DEFINED Defined when weak references are defined for interfaces.
*New* in XE4/iOS.


Attention: The symbols followed by an asterisk (*) were defined for Delphi mobile compilers in the past, but they have been removed in RAD Studio 10.4 Sydney as part of the removal of the ARC memory model.

In the table column heads:

Framework Conditional variables

The following conditionals are available as of RAD Studio 11.1:

Category Symbol Comments
Framework FRAMEWORK_VCL Defined if the project uses VCL framework.
FRAMEWORK_FMX Defined if the project uses FMX framework.

Using Conditional Defines for the Compiler Version

For example, to determine the version of the compiler and run-time library that were used to compile your code, you can use {$IF} with the CompilerVersion, RTLVersion and other constants: 

 {$IFDEF CONDITIONALEXPRESSIONS}
    {$IF CompilerVersion >= 17.0}
      {$DEFINE HAS_INLINE}
    {$IFEND}
    {$IF RTLVersion >= 14.0}
      {$DEFINE HAS_ERROUTPUT}
    {$IFEND}
 {$ENDIF}

See the table of Compiler Versions for a list of version numbers associated with various released Delphi compilers.

Predefined Constants

Constants can be more powerful than conditionals because you can use constants programmatically in Delphi code. Conditionals, on the other hand, are accepted only inside conditional compiler directives such as {$IF} and {$IFDEF}.

There are three important constants available:

  • System.RTLVersion is a constant defined as the version of the run-time library. For Sydney, RTLVersion is 34.
  • System.CompilerVersion is a constant defined as the version of the current Delphi compiler. For Sydney, CompilerVersion is 34.
  • FMX.Types.FireMonkeyVersion is a constant defined as the version of the current FireMonkey library. For Sydney, FireMonkeyVersion is 270.

See Also

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