Errors are disappeared when build again

I’m using visual studio 2015 and writing codes for plugin.

I met unresolved external symbol error, but it’s disappeared if I build again without modifying my codes.

here is build output message.

------ Build started: Project: UE4, Configuration: BuiltWithUnrealBuildTool Win32 ------
------ Build started: Project: MyFirstTopDown, Configuration: Development_Editor x64 ------
  Compiling game modules for hot reload
  Target is up to date
========== Build: 2 succeeded, 0 failed, 0 up-to-date, 0 skipped ==========

After modify codes and build projects, error appears!
What’s the problem?

Additional informations:

here is my simple plugin class

class FMyModule : public IModuleInterface
{
public:
	/** IModuleInterface implementation */
	virtual void StartupModule() override;
	virtual void ShutdownModule() override;

	static FMyModule& Get();

	void SendLog(const FString&);

private:
	/** Handle to the test dll we will load */
	void*	ExampleLibraryHandle;

	static FMyModule* Singleton;
};

and here is how do I call this plugin’s method and error log:

FString log = FString::Printf(TEXT("tick %d"), ++logSent);

UE_LOG(LogTemp, Warning, TEXT("%s"), *log);

FMyModule::Get().SendLog(log);

FMyModule::Get().SendLog("abcd");

Severity	Code	Description	Project	File	Line	Suppression State
Error	LNK2019	unresolved external symbol "public: static class FMyModule & __cdecl FMyModule::Get(void)" (?Get@FMyModule@@SAAEAV1@XZ) referenced in function "public: virtual void __cdecl AMyFirstTopDownCharacter::Tick(float)" (?Tick@AMyFirstTopDownCharacter@@UEAAXM@Z)	MyFirstTopDown	C:\Users\juhong.jung\Documents\Unreal Projects\MyFirstTopDown\Intermediate\ProjectFiles\MyFirstTopDownCharacter.cpp.obj	1	
Error	LNK2019	unresolved external symbol "public: void __cdecl FMyModule::SendLog(class FString const &)" (?SendLog@FMyModule@@QEAAXAEBVFString@@@Z) referenced in function "public: virtual void __cdecl AMyFirstTopDownCharacter::Tick(float)" (?Tick@AMyFirstTopDownCharacter@@UEAAXM@Z)	MyFirstTopDown	C:\Users\juhong.jung\Documents\Unreal Projects\MyFirstTopDown\Intermediate\ProjectFiles\MyFirstTopDownCharacter.cpp.obj	1

Hey juhong-

Can you provide the errors you’re getting? From the build output posted, there does not appear to be any errors occurring. Additionally, can you try closing the project and compile again. Let me know if this gives you the same errors. If possible, please also include any custom source code in your project to help identify where the unresolved external errors are coming from.

I didn’t think my error is required for answer because it was just unresolved external symbol error. (yes. it’s really common error). I put additional information. Thanks for your attention :slight_smile:

Now, I understand. It meant target is up to date. In my opinion, it’s weird… Why they don’t show errors again and why unresolved external symbol error is occurred? My plugin is included by adding PrivateDependencyModuleNames