postprocessingComponent c++ linking error

As the title says, when creating a child class of UPostProcessingComponent, I got a linking error when building. am i missing a module?
I realized that the linker cannot find these 3 functions:

void UPostProcessComponent::OnRegister();
void UPostProcessComponent::OnUnregister();
void UPostProcessComponent::Serialize(FArchive& Ar);

I also found that they are in the UnrealClient.cpp file, which is in the Engine module, however, the engine module is already included, is it possible that this part of the translation unit is not included because of some Preprocessor Directives? and why are they not in the PostProcessComponent.cpp file? Will I have to specify a target platform or something?

Thanks a lot!

My current solution is to just copy the implementation to the .cpp file of the child class so the linker can find it… seems like the wrong way of doing it…

you need to add ENGINE_API to these function at the front