In this lesson, you will learn how to drastically speed up your build times by strategically using Precompiled Headers and organizing your code into smaller, independent modules.
As your game grows, recompiling every single file every time you make a tiny change becomes incredibly slow. Unreal Engine combats this using a system called Precompiled Headers (PCH).
What is a Precompiled Header?
Normally, when you include a header file (like CoreMinimal.h) in your C++ files, the compiler has to process that same file over and over again for every single .cpp file in your project. A Precompiled Header acts as a "snapshot" of these commonly used headers. Instead of re-parsing them every time, the compiler loads the pre-processed snapshot, which saves massive amounts of time.
In your Module.Build.cs files, you can define your PCH usage. A common best practice is to set PCHUsage = PCHUsageMode.UseExplicitOrSharedPCHs;. This tells the engine to create a shared header that contains the most essential project-wide files, ensuring your project only compiles what is absolutely necessary.
Modularizing for Speed
Another way to optimize is by splitting your project into multiple Modules. If you keep all your code in one giant module, any change—no matter how small—forces the engine to re-verify the entire project.
By separating your project into logical modules (e.g., a Core module, a Player module, and a UI module), you isolate your code. When you modify a file in the UI module, the Core module remains untouched and does not need to be recompiled. You define these relationships in your Target.cs or Build.cs files, keeping your dependency graph clean:
// Inside your Build.cs file
PublicDependencyModuleNames.AddRange(new string[] {
"Core",
"CoreUObject",
"Engine",
"InputCore"
});
By keeping your modules focused and using PCHs to handle common includes, you minimize the "compilation footprint" of your changes. This is the difference between waiting five minutes for a build versus waiting five seconds.
Key Takeaway: Faster compilation is achieved by using Precompiled Headers to cache common dependencies and splitting your code into independent modules to ensure that only the modified parts of your project need to be recompiled.