Platform dependent compilation

Unity’s Platform Dependent Compilation feature consists of some preprocessor directives that let you partition 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 compile and execute a section of code exclusively for one of the supported platforms.

You can run this code within the Unity Editor, so you can compile the code specifically for your target platform and test it in the Editor.

Platform #define directives

The platform #define directives that Unity supports for your scripts are as follows:

You can also compile code selectively. The options available depend on the version of the Editor that you are working on. Given a version number X.Y.Z (for example, 2.6.0), Unity exposes three global #define directives in the following formats: UNITY_X, UNITY_X_Y and UNITY_X_Y_Z.

Here is an example of #define directives exposed in Unity 5.0.1:

Starting from Unity 5.3.4, you can 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.Z), Unity exposes one global #define in the format UNITY_X_Y_OR_NEWER, that can be used for this purpose.

The supported #define directives are:

You use the DEVELOPMENT_BUILD #define to identify whether 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.

You can also compile code selectively depending on the scripting back-end.

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.

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:

// C#
using UnityEngine;
using System.Collections;

public class PlatformDefines : MonoBehaviour {
  void Start () {

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

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

    #if UNITY_STANDALONE_WIN
      Debug.Log("Stand Alone 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 “Iphone” 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 iPhone");

#else
    Debug.Log("Any other platform");

#endif

Platform custom #defines

It is also possible to add to the built-in selection of #define directives by supplying your own. Open the Other Settings panel of the Player settings and navigate to the Scripting Define Symbols text box.

Enter the names of the symbols you want to define for that particular platform, separated by semicolons. These symbols can then be used as the conditions for #if directives, just like the built-in ones.

Global custom #defines

You can define your own preprocessor directives to control which code gets included when compiling. To do this you must add a text file with the extra directives to the AssetsAny media or data that can be used in your game or project. An asset may come from a file created outside of Unity, such as a 3D Model, an audio file or an image. You can also create some asset types in Unity, such as an Animator Controller, an Audio Mixer or a Render Texture. More info
See in Glossary folder. The name of the file depends on the language you are using. The extension is .rsp:

As an example, if you include the single line -define:UNITY_DEBUG in your mcs.rsp file, the #define directive UNITY_DEBUG exists as a global #define for C# scripts, except for Editor scripts.

Every time you make changes to .rsp files, you need to recompile in order for them to be effective. You can do this by updating or reimporting a single script (.js or .cs) file.

Note: If you want to modify only global #define directives, use Scripting Define Symbols in Player settings, because this covers all the compilers. If you choose the .rsp files instead, you need to provide one file for every compiler Unity uses.

The use of .rsp files is described in the ‘Help’ section of the mcs application, which is included in the Editor installation folder. You can get more information by running mcs -help.

Note that the .rsp file needs to match the compiler being invoked. For example:

• when targeting the .NET 3.5 Equivalent (deprecated) scripting runtime version, mcs is used with mcs.rsp, and
• when targeting the .NET 4.x Eqivalent scripting runtime version compiler, csc is used with csc.rsp.