Availability:Public
Title:Configuring Unreal Build System
Crumbs: %ROOT%, Programming, Programming/UnrealBuildSystem
Description:Configuring Unreal Build System to control  how the engine is built.
Version: 4.5

The Unreal Build System can be configured through the `BuildConfiguration.cs` to modify the build process to suit a variety of needs.

## UnrealBuldTool Configuration Properties

$ bStopXGECompilationAfterErrors : If _true_, compilation with XGE will stop when an error occurs.
    * Continuing compiling makes subsequent compiles much faster after you fix the odd error.
    * It lets you see compile errors in all files before quitting the build.
    * You can use **Ctrl + Break** to interrupt a failed build.
$ bOmitPCDebugInfoInDevelopment : If _true_, debug info is not included when building in Development configuration.
    * Set to _false_ to always include debug info.
    * Including debug info slows down compiling, but gives you line numbers and stack info in Development builds.
$ bUseUnityBuild : Set to _true_ when rebuilding the engine as a whole. This should be disabled when using fast iteration mode. See [Build Modes](#BuildModes) for more information.
$ bEnableFastIteration : If _true_, compile and link times are dramatically decreased. This should be disabled when creating unity builds. See [Build Modes](#BuildModes) for more information.
    * Setting to _true_ gives fastest iteration times.
    * If you encounter weird "RPC" or "PDB" link errors, then you should set `bUseIncrementalLinking=false` in `ValidateConfiguration()`


## Build Modes

There are two build modes: **unity** and **fast iteration**. Unity is good for making changes that require rebuilding the whole engine e.g. changing an Engine header. Fast iteration is good when you are making localized changes - it gets your compile/link time down to less than 4 seconds. To change between the two, open `BuildConfiguration.cs` and find the lines:

	bEnableFastIteration = Utils.GetEnvironmentVariable( "ue.bEnableFastIteration", false );
	bUseUnityBuild = Utils.GetEnvironmentVariable("ue.bUseUnityBuild", true);

This can be modified to force the one you want to be `true`. Unity is the default.