Version: 2021.3
Special folders and script compilation order
Custom scripting symbols

Conditional Compilation

Unity’s support for the C# language includes the use of directives, which allow you to selectively include or exclude code from compilation, based on whether certain scripting symbols are defined or not defined.

You can read more broadly about how these directives work in C# on the Microsoft C# preprocessor directives page.

Unity has a range of built-in scripting symbols which represent options that you can use in your scriptsA piece of code that allows you to create your own Components, trigger game events, modify Component properties over time and respond to user input in any way you like. More info
See in Glossary
to selectively include or exclude portions of code from compilation.

For example, the built-in scripting symbol that is set when a player is built for Windows standalone platform is UNITY_STANDALONE_WIN. You can check whether this symbol is defined using a special type of if statement, as follows:

#if UNITY_STANDALONE_WIN

  Debug.Log("Standalone Windows");

#endif

The hash (#) character in front of the if and endif indicates that these statements are “directives”, and are handled during the compilation process, rather than at runtime.

Therefore in the above example, the Debug line is only included for compilation in the Windows standalone build of the project. It is omitted entirely when compiled in the Editor, or in other target builds. This is different to using a regular if .. then .. else structure, which would only bypass the execution of certain portions of code at run time. See further below for full examples.

There are a number of built-in scripting symbols which allow you to selectively compile or omit code based on the selected Platform, the Editor Version, and other miscellaneous system environment scenarios. These built-in scripting symbols are listed below.

In addition, you can define your own scripting symbols either using the Editor UI(User Interface) Allows a user to interact with your application. Unity currently supports three UI systems. More info
See in Glossary
, via scripting, or via an asset file, which allows you to control compilation of portions of your code based on arbitrary definitions. See Custom scripting symbols for more information.

Note: Scripting symbols are sometimes referred to as “define symbols”, “preprocessor defines”, or just “defines”.

Platform scripting symbols

Unity automatically defines certain scripting symbols based on the authoring and build target platform. These are as follows:

Define Function
UNITY_EDITOR Scripting symbol to call Unity Editor scripts from your game code.
UNITY_EDITOR_WIN Scripting symbol for Editor code on Windows.
UNITY_EDITOR_OSX Scripting symbol for Editor code on Mac OS X.
UNITY_EDITOR_LINUX Scripting symbol for Editor code on Linux.
UNITY_STANDALONE_OSX Scripting symbol to compile or execute code specifically for Mac OS X (including Universal, PPC and Intel architectures).
UNITY_STANDALONE_WIN Scripting symbol for compiling/executing code specifically for Windows standalone applications.
UNITY_STANDALONE_LINUX Scripting symbol for compiling/executing code specifically for Linux standalone applications.
UNITY_STANDALONE Scripting symbol for compiling/executing code for any standalone platform (Mac OS X, Windows or Linux).
UNITY_WII Scripting symbol for compiling/executing code for the Wii console.
UNITY_IOS Scripting symbol for compiling/executing code for the iOS platform.
UNITY_IPHONE Deprecated. Use UNITY_IOS instead.
UNITY_ANDROID Scripting symbol for the Android platform.
UNITY_LUMIN Scripting symbol for the Magic Leap OS platform. You can also use PLATFORM_LUMIN.
UNITY_TIZEN Scripting symbol for the Tizen platform.
UNITY_TVOS Scripting symbol for the Apple TV platform.
UNITY_WSA Scripting symbol for Universal Windows PlatformAn IAP feature that supports Microsoft’s In App Purchase simulator, which allows you to test IAP purchase flows on devices before publishing your application. More info
See in Glossary
. Additionally, NETFX_CORE is defined when compiling C# files against .NET Core and using .NET scripting backendA framework that powers scripting in Unity. Unity supports three different scripting backends depending on target platform: Mono, .NET and IL2CPP. Universal Windows Platform, however, supports only two: .NET and IL2CPP. More info
See in Glossary
.
UNITY_WSA_10_0 Scripting symbol for Universal Windows Platform. Additionally WINDOWS_UWP is defined when compiling C# files against .NET Core.
UNITY_WEBGL Scripting symbol for WebGLA JavaScript API that renders 2D and 3D graphics in a web browser. The Unity WebGL build option allows Unity to publish content as JavaScript programs which use HTML5 technologies and the WebGL rendering API to run Unity content in a web browser. More info
See in Glossary
.
UNITY_FACEBOOK Scripting symbol for the Facebook platform (WebGL or Windows standalone).
UNITY_ANALYTICS Scripting symbol for calling Unity AnalyticsAbbreviation of Unity Analytics
See in Glossary
methods from your game code. Version 5.2 and above.
UNITY_ASSERTIONS Scripting symbol for assertions control process.
UNITY_64 Scripting symbol for 64-bit platforms.

Editor version Scripting symbols

Unity automatically defines certain scripting symbols based on the version of the Editor that you are currently using.

Given a version number X.Y.Z (for example, 2019.4.14), Unity exposes three global scripting symbols in the following formats: UNITY_X, UNITY_X_Y and UNITY_X_Y_Z.

Here is an example of scripting symbols exposed in Unity 2019.4.14:

Define Function
UNITY_2019 Scripting symbol for the release version of Unity 2019, exposed in every 2019.Y.Z release.
UNITY_2019_4 Scripting symbol for the major version of Unity 2019.4, exposed in every 2019.4.Z release.
UNITY_2019_4_14 Scripting symbol for the minor version of Unity 2019.4.14.

You can also compile code selectively based on the earliest version of Unity required to compile or execute a given portion of code. Given the same version format as above (X.Y), Unity exposes one global #define in the format UNITY_X_Y_OR_NEWER, that you can use for this purpose.

Other scripting symbols

The other scripting symbols Unity defines are:

Define Function
CSHARP_7_3_OR_NEWER Defined when building scripts with support for C# 7.3 or newer.
ENABLE_MONO Scripting backend #define for Mono.
ENABLE_IL2CPP Scripting backend #define for IL2CPPA Unity-developed scripting back-end which you can use as an alternative to Mono when building projects for some platforms. More info
See in Glossary
.
NET_2_0 Defined when building scripts against .NET 2.0 API compatibility level on Mono and IL2CPP.
NET_2_0_SUBSET Defined when building scripts against .NET 2.0 Subset API compatibility level on Mono and IL2CPP.
NET_LEGACY Defined when building scripts against .NET 2.0 or .NET 2.0 Subset API compatibility level on Mono and IL2CPP.
NET_4_6 Defined when building scripts against .NET 4.x API compatibility level on Mono and IL2CPP.
NET_STANDARD_2_0 Defined when building scripts against .NET Standard 2.0 API compatibility level on Mono and IL2CPP.
NET_STANDARD_2_1 Defined when building scripts against .NET Standard 2.1 API compatibility level on Mono and IL2CPP.
NET_STANDARD Defined when building scripts against .NET Standard 2.1 API compatibility level on Mono and IL2CPP.
NETSTANDARD2_1 Defined when building scripts against .NET Standard 2.1 API compatibility level on Mono and IL2CPP.
NETSTANDARD Defined when building scripts against .NET Standard 2.1 API compatibility level on Mono and IL2CPP.
ENABLE_WINMD_SUPPORT Defined when Windows Runtime support is enabled on IL2CPP. See Windows Runtime Support for more details.
ENABLE_INPUT_SYSTEM Defined when the Input System package is enabled in Player SettingsSettings that let you set various player-specific options for the final game built by Unity. More info
See in Glossary
.
ENABLE_LEGACY_INPUT_MANAGER Defined when the legacy Input ManagerSettings where you can define all the different input axes, buttons and controls for your project. More info
See in Glossary
is enabled in Player Settings.
UNITY_SERVER Defined when the Server Build setting is enabled in Build Settings
DEVELOPMENT_BUILD Defined when your script is running in a player which was built with the “Development BuildA development build includes debug symbols and enables the Profiler. More info
See in Glossary
” option enabled.

Testing precompiled code

Below is an example of how to use the precompiled code. It prints a message that depends on the platform you have selected for your target build.

First of all, select the platform you want to test your code against by going to File > Build Settings. This displays the Build Settings window; select your target platform from here.

Build Settings window with Windows, Mac, Linux selected as the target platform
Build Settings window with Windows, Mac, Linux selected as the target platform

Select the platform you want to test your precompiled code against and click Switch Platform to tell Unity which platform you are targeting.

Create a script and copy/paste the following code:

using UnityEngine;
using System.Collections;

public class PlatformDefines : MonoBehaviour {
  void Start () {

    #if UNITY_EDITOR
      Debug.Log("Unity Editor");
    #endif

    #if UNITY_IOS
      Debug.Log("iOS");
    #endif

    #if UNITY_STANDALONE_OSX
        Debug.Log("Standalone OSX");
    #endif

    #if UNITY_STANDALONE_WIN
      Debug.Log("Standalone Windows");
    #endif

  }          
}

To test the code, click Play Mode. Confirm that the code works by checking for the relevant message in the Unity console, depending on which platform you selected - for example, if you choose iOSApple’s mobile operating system. More info
See in Glossary
, the message “Unity iOS” is set to appear in the console.

In C# you can use a CONDITIONAL attribute which is a more clean, less error-prone way of stripping out functions. See ConditionalAttribute Class for more information. Note that common Unity callbacks (ex. Start(), Update(), LateUpdate(), FixedUpdate(), Awake()) are not affected by this attribute because they are called directly from the engine and, for performance reasons, it does not take them into account.

In addition to the basic #if compiler directive, you can also use a multiway test in C#:

#if UNITY_EDITOR

    Debug.Log("Unity Editor");

#elif UNITY_IOS

    Debug.Log("Unity iOS");

#else

    Debug.Log("Any other platform");

#endif
Special folders and script compilation order
Custom scripting symbols