Platform Defines Macros
The platform defines that Unity supports for your scripts are:
| UNITY_EDITOR | Define for calling Unity Editor scripts from your game code. |
| UNITY_STANDALONE_OSX | Platform define for compiling/executing code specifically for Mac OS (This includes Universal, PPC and Intel architectures). |
| UNITY_DASHBOARD_WIDGET | Platform define when creating code for Mac OS dashboard widgets. |
| UNITY_STANDALONE_WIN | Use this when you want to compile/execute code for Windows stand alone applications. |
| UNITY_STANDALONE_LINUX | Use this when you want to compile/execute code for Linux stand alone applications. |
| UNITY_WEBPLAYER | Platform define for web player content (this includes Windows and Mac Web player executables). |
| UNITY_WII | Platform define for compiling/executing code for the Wii console. |
| UNITY_IPHONE | Platform define for compiling/executing code for the iPhone platform. |
| UNITY_ANDROID | Platform define for the Android platform. |
| UNITY_PS3 | Platform define for running PlayStation 3 code. |
| UNITY_XBOX360 | Platform define for executing Xbox 360 code. |
| UNITY_NACL | Platform define when compiling code for Google native client (this will be set additionally to UNITY_WEBPLAYER). |
| UNITY_FLASH | Platform define when compiling code for Adobe Flash. |
Also you can compile code selectively depending on the version of the engine you are working on. Currently the supported ones are:
| UNITY_2_6 | Platform define for the major version of Unity 2.6. |
| UNITY_2_6_1 | Platform define for specific version 1 from the major release 2.6. |
| UNITY_3_0 | Platform define for the major version of Unity 3.0. |
| UNITY_3_0_0 | Platform define for the specific version 0 of Unity 3.0. |
| UNITY_3_1 | Platform define for major version of Unity 3.1. |
| UNITY_3_2 | Platform define for major version of Unity 3.2. |
| UNITY_3_3 | Platform define for major version of Unity 3.3. |
| UNITY_3_4 | Platform define for major version of Unity 3.4. |
| UNITY_3_5 | Platform define for major version of Unity 3.5. |
| UNITY_4_0 | Platform define for major version of Unity 4.0. |
来源：https://www.cnblogs.com/dayhand/p/3990559.html