What's changed with linking in 4.4?

Development Programming & Scripting
1

I’ve just synced my 4.3 fork of the engine with 4.4 and got it compiling. However, when it gets to the linker I get a ton of linker errors in my new AGameMode super class. This code compiles, links and ran in UE4.3, so I’m not sure what’s changed.

The class is defined like so:

UCLASS(config = Game, notplaceable, BlueprintType, Blueprintable, hidecategories = (Info, Rendering, MovementReplication, Replication, Actor))
class ENGINE_API ABaseGameMode : public AInfo
{
	GENERATED_UCLASS_BODY()

	/** Restart the game, by default travel to the current map */
	virtual void RestartGame();

The first method there is one of the first to throw a linker error. There’s 71 of them, here’s the first 3:

27>EnginePrivate.h.obj : error LNK2001: unresolved external symbol "public: virtual void __cdecl ABaseGameMode::RestartGame(void)" (?RestartGame@ABaseGameMode@@UEAAXXZ)
27>EnginePrivate.h.obj : error LNK2001: unresolved external symbol "public: virtual void __cdecl ABaseGameMode::ReturnToMainMenuHost(void)" (?ReturnToMainMenuHost@ABaseGameMode@@UEAAXXZ)
27>Module.Engine.5_of_30.cpp.obj : error LNK2001: unresolved external symbol "public: virtual void __cdecl ABaseGameMode::ReturnToMainMenuHost(void)" (?ReturnToMainMenuHost@ABaseGameMode@@UEAAXXZ)

Been doing some reading on the Unreal Build Tool and will continue to do so, but I have no idea why it’s not linking this. There’s some config somewhere preventing it I assume.

How does this work, and how do I fix this?

2

Are you making these changes directly in the Engine module? If so… not a good idea. You should be creating your game mode classes in your own modules.

If this class is already in your own module, then ENGINE_API is wrong. It must be YOURMODULE_API instead.

You will probably also want to inherit from AGameMode, not AInfo.

3

Thanks for the feedback. This is an engine refactor, that’s why I mentioned it was a fork of 4.3. I’m packaging a pull request.

4

Assuming that your class actually has a definition for ReturnToMainMenuHost then this should work. Have you tried deleting the Intermediates directory and doing a full rebuild after upgrading?

5

I rebuilt the project files using the batch file, did a full solution clean and rebuild, but didn’t delete the intermediates directory. Didn’t realize it was necessary. Deleted, ran the batch, cleaned and rebuilding now.

6

Still failing to link in the same way. Anything else I should try?

7

Where are the implementations of ABaseGameMode::ReturnToMainMenuHost and ABaseGameMode::RestartGame located at?

8

Thanks, for some reason the merge deleted ABaseGameMode.cpp which was where it was supposed to be. I have no idea why. Git is a mystery. Restoring that file caused it to link without issues. Thanks again!