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.
Contents
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 |
DCCOSX Since XE2 |
DCCIOSARM Since XE3 |
DCCIOS32 Since XE3 |
DCCAARM In XE5 |
DCCIOSARM64 Since XE8 |
DCCLINUX64 Since 10.2 Tokyo |
Comments |
---|---|---|---|---|---|---|---|---|---|---|
Compiler | DCC | DEFINED | DEFINED | DEFINED | DEFINED | DEFINED | DEFINED | DEFINED | DEFINED | |
VER320 For a list of compiler versions, see Compiler Versions. |
DEFINED | DEFINED | DEFINED | DEFINED | DEFINED | DEFINED | DEFINED | DEFINED | For Delphi Tokyo, compiler version 32.0 has VER320 defined.
| |
Platform | CONSOLE | 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 | DEFINED | DEFINED | N/A | DEFINED | not defined | Defined if the target platform is iOS. *New* in XE4/iOS | |
IOS32 | not defined | not defined | not defined | DEFINED | DEFINED | not defined | not defined | not defined | Defined if the target platform is iOS32. Since XE8/iOSarm64 | |
IOS64 | not defined | not defined | not defined | not defined | not defined | not defined | DEFINED | not defined | Defined if the target platform is iOS64. Since XE8/iOSarm64 | |
NATIVECODE | 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 | 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 | 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 | Target platform is 64-bit Windows. *New* in XE2/x64 | |
MACOS | not defined | not defined | DEFINED | DEFINED | DEFINED | not defined | DEFINED | not defined | Target platform is OS X. *New* in XE2/OSX | |
MACOS32 | not defined | not defined | DEFINED | DEFINED | DEFINED | not defined | not defined | not defined | Target platform is 32-bit OS X. *New* in XE2/OSX | |
MACOS64 | not defined | not defined | not defined | not defined | not defined | not defined | DEFINED | not defined | Target platform is 64-bit OS X. *New* in XE8/OSX | |
LINUX | not defined | not defined | not defined | not defined | not defined | not defined | not defined | DEFINED | Since Kylix | |
LINUX32 | 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 | not defined | not defined | DEFINED | New in 10.2 | |
POSIX | not defined | not defined | DEFINED | DEFINED | DEFINED | DEFINED | DEFINED | DEFINED | Since Kylix | |
POSIX32 | not defined | not defined | DEFINED | DEFINED | DEFINED | DEFINED | DEFINED | not defined | Since Kylix | |
POSIX64 | not defined | not defined | not defined | not defined | not defined | not defined | DEFINED | DEFINED | Since Kylix | |
ANDROID | not defined | not defined | not 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 | not defined | not defined | DEFINED | not defined | not defined | Since XE8/iOSarm64 | |
CPU | CPU386 | DEFINED | not defined | DEFINED | not defined | DEFINED | not defined | not defined | note defined | Indicates that the CPU is an Intel 386 or later. |
CPUX86 | DEFINED | not defined | DEFINED | not defined | 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 | not defined | not defined | not defined | not defined | not defined | DEFINED | The CPU supports the x86-64 instruction set, and is in a 64-bit environment. *New* in XE2/x64 | |
CPU32BITS | DEFINED | not defined | DEFINED | DEFINED | DEFINED | DEFINED | not defined | not defined | The CPU is in a 32-bit environment, such as DCC32.EXE. *New* in XE8 | |
CPU64BITS | not defined | DEFINED | not defined | not defined | not defined | not 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 | not defined | DEFINED | DEFINED | not defined | Defined if the CPU is based on the ARM architecture, such as the Delphi mobile compiler for the iOS device (DCCIOSARM.EXE). *New* in XE4/iOS | |
CPUARM32 | not defined | not defined | not defined | DEFINED | not defined | DEFINED | not defined | not defined | The CPU is in a 32-bit ARM environment, such as DCCIOSARM.EXE. *New* in XE8 | |
CPUARM64 | not defined | not defined | not defined | not defined | not defined | not defined | DEFINED | not defined | The CPU is in a 64-bit ARM environment, such as DCCIOSARM64.EXE. *New* in XE8 | |
Availability | ||||||||||
ALIGN_STACK | not defined | not defined | DEFINED | not defined | DEFINED | not defined | not defined | not defined | Defined in code that may be shared with the OS X 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/OSX | |
ASSEMBLER | DEFINED | DEFINED | DEFINED | not defined | DEFINED | not defined | not defined | not defined | Assembler syntax is accepted. | |
AUTOREFCOUNT | not defined | not defined | not defined | DEFINED | DEFINED | DEFINED | DEFINED | DEFINED | Defined for compilers that use automatic reference counting, such as the Delphi mobile compilers. *New* in XE4/iOS | |
EXTERNALLINKER | not defined | not defined | not defined | DEFINED | not 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 | UNICODE is defined as the default string type. | |
CONDITIONALEXPRESSIONS | 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 | not defined | not defined | DEFINED | Defined when targeting Executable and Linkable Format (ELF) files. | |
NEXTGEN | not defined | not defined | not defined | DEFINED | DEFINED | DEFINED | DEFINED | 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 | |
PC_MAPPED_EXCEPTIONS | not defined | not defined | DEFINED | not defined | 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 OS X). *New* in XE2. | |
PIC | never | never | always DEFINED | never | always DEFINED | always DEFINED | never | always DEFINED | Defined for platforms that require Position-Independent Code (PIC), such as OS X. | |
UNDERSCOREIMPORTNAME | DEFINED | not defined | DEFINED | not defined | 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 for compilers that can use weak references (the [weak] attribute). *New* in XE4/iOS | |
WEAKINSTREF | not defined | not defined | not defined | DEFINED | DEFINED | DEFINED | DEFINED | DEFINED | Defined when weak references are defined for instances. *New* in XE4/iOS | |
WEAKINTFREF | DEFINED | DEFINED | DEFINED | DEFINED | DEFINED | DEFINED | DEFINED | DEFINED | Defined when weak references are defined for interfaces. *New* in XE4/iOS |
In the table column heads:
- DCC32 is the 32-bit Windows Delphi compiler.
- DCC64 is the 64-bit Windows Delphi compiler.
- DCCOSX is the OS X Delphi compiler.
- DCCIOSARM is the Delphi compiler for 32-bit iOS Devices.
- DCCIOS32 is the Delphi compiler for iOS Simulators.
- DCCAARM.EXE is the Delphi compiler for Android devices.
- DCCIOSARM64 is the Delphi compiler for 64-bit iOS devices.
- DCCLINUX64 is the 64-bit Linux Delphi compiler.
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 Tokyo, RTLVersion is 32.
- System.CompilerVersion is a constant defined as the version of the current Delphi compiler. For Tokyo, CompilerVersion is 32.
- FMX.Types.FireMonkeyVersion is a constant defined as the version of the current FireMonkey library. For Tokyo, FireMonkeyVersion is 250.