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C++ Build Compile Link errors.md

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2021-02-18_20:36:29

C++ Build Compile Link errors

Undefined symbol on StaticEnum

ld.lld: error: undefined symbol: UEnum* StaticEnum<FMyClass::EMyEnum>()

This happens when an UENUM is nested inside a class. Move the enum up to file scope. It's possible that marking the class with UCLASS (or USTRUCT for structs) will also fix it, haven't tried.

File not found

fatal error: 'MyHeader.h' file not found

This happens when we have a #include <MyHeader.h> or #include "MyHeader.h" in our code without telling the compiler where MyHeader is. Unreal Build Tool handle most of this for us, but we need to give it some hints.

Some possible causes:

  • The module that provides the header file is not listed in (Public|Private)DependencyModuleNames in .Build.cs. Check the Module row of the class' page in the Unreal Engine API Reference to see which module to include.
  • The header file is actually in a subdirectory so more of the path must be given. This is a tricky one because it builds without the directory in the #include when building in Development mode but not when cooking/exporting. Check the Include row of the class' page in the Unreal Engine API Reference to see the correct include path.

Undefined symbol GetPrivateStaticClass

ld.lld: error: undefined symbol: UMyComponent::GetPrivateStaticClass()

And then a reference to the GENERATED_BODY() line in the Component's header file.

The MYMODULE_API tag/marker/decorator is missing from the Component's class declaration. This solution is applicable to a number of undefined symbol related errors.

Most other linker errors

Often one of the following reasons:

  • A required module hasn't been added to your .Build.cs Add(Public|Private)DependencyMOduleNames. Read the linker error message to determine which function it doesn't find and use docs.unrealengine.com to learn what module to add. If there is no documentation for what you need then open the header file you got the symbol from and check what .*_API macro it uses.
  • You forgot to implement a function in one of your classes. The function is listed in the header file so the source can be compiled, but at link time the code for the function wasn't found.
  • The function/class you're using isn't exported from its module. Functions and classes are exported with the MYMODULE_API macros place before the symbol name.

[[2020-09-18_08:51:49]] Build.cs