If the player kills the NPC, it crashes

[sehwa]

Hi, I’m trying to pop up a UI that says I won if the player killed the NPC.
But now I have a problem. Crash has occurred.
Let me show you the crash first.

LoginId:c94d24654bb053080c17c2ad5040f05a
EpicAccountId:fccedefcd3d646a6a9f2c9f009701903

Unhandled Exception: EXCEPTION_ACCESS_VIOLATION reading address 0x0000000000000458

UnrealEditor_LifeOfLuck!UE::CoreUObject::Private::ResolveObjectHandleNoRead() [D:\UE_5.3\Engine\Source\Runtime\CoreUObject\Public\UObject\ObjectHandle.h:256]
UnrealEditor_LifeOfLuck!AOLGameMode::DeadCheck() [D:\Project\LifeOfLuck\Source\LifeOfLuck\GameMode\OLGameMode.cpp:35]
UnrealEditor_LifeOfLuck!AOLCharacterBase::TakeDamage() [D:\Project\LifeOfLuck\Source\LifeOfLuck\Character\OLCharacterBase.cpp:182]
UnrealEditor_LifeOfLuck!AOLCharacterBase::AttackHitCheck() [D:\Project\LifeOfLuck\Source\LifeOfLuck\Character\OLCharacterBase.cpp:153]
UnrealEditor_Engine
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kernel32
ntdll

And now I’m going to show you my code.

float AOLCharacterBase::TakeDamage(float DamageAmount, struct FDamageEvent const& DamageEvent, AController* EventInstigator, AActor* DamageCauser)
{
	Super::TakeDamage(DamageAmount, DamageEvent, EventInstigator, DamageCauser);

	Hp = FMath::Clamp(Hp - DamageAmount, 0.0f, MaxHp);	// 체력  업데이트

	UE_LOG(LogTemp, Warning, TEXT("Damage = %f"), DamageAmount);
	UE_LOG(LogTemp, Warning, TEXT("Hp = %f"), Hp);

	// 체력이 0 이하인 경우
	if (Hp <= 0.0f)
	{
		AOLGameMode* GameMode = Cast<AOLGameMode>(GetWorld()->GetAuthGameMode());	// 게임모드 가져오기
		if (GameMode)
		{
			GameMode->DeadCheck(this);	// 어떤 캐릭터가 죽었는지 확인
		}

		Dead();	// 죽었으니 함수 호출

		UE_LOG(LogTemp, Error, TEXT("Dead!"));
	}

	return DamageAmount;
}

AOLGameMode::AOLGameMode()
{
	NPCs = 0;
}

void AOLGameMode::BeginPlay()
{
	Super::BeginPlay();

	GameStart();
}

void AOLGameMode::GameStart()
{
	NPCs = NPCCount();	// 월드에 있는 NPC 수 초기화

	UE_LOG(LogTemp, Warning, TEXT("NPC is %d"), NPCs);
}

void AOLGameMode::DeadCheck(ACharacter* Character)
{
	// 캐릭터로 확인
	Player = Cast<AOLCharacterPlayer>(Character);
	NPC = Cast<AOLNPCBasic>(Character);

	// 플레이어가 죽은 경우
	if (Character == Player)
	{
		AOLPlayerController* PlayerController = Cast<AOLPlayerController>(Player->GetController());	// 플레이어의 컨트롤러 가져오기

		if (PlayerController)
		{
			PlayerController->GameOver();
		}
	}
	// NPC가 죽은 경우
	else if (Character == NPC)
	{
		NPCs--;	// NPC가 죽으면 1 빼주기(NPC 수 차감)

		AOLPlayerController* PlayerController = Cast<AOLPlayerController>(Player->GetController());	// 플레이어의 컨트롤러 가져오기

		// 월드에 있는 모든 NPC가 죽은 경우
		if (NPCs == 0)
		{
			if (PlayerController != nullptr)
			{
				PlayerController->GameClear();
			}
			else
			{
				UE_LOG(LogTemp, Error, TEXT("No PlayerController"));
			}
		}
	}

}

int32 AOLGameMode::NPCCount()
{
	TArray<AActor*> AllNPC;	// 월드에 있는 모든 NPC를 담을 배열

	// 월드에 NPC 클래스로 되어있는 모든 액터들을 배열에 넣어주기
	UGameplayStatics::GetAllActorsOfClass(GetWorld(), AOLNPCBasic::StaticClass(), AllNPC);
	UE_LOG(LogTemp, Display, TEXT("ALLNPC: %d"), AllNPC.Num());

	return AllNPC.Num();	// 월드에 있는 모든 NPC 수 반환
}

The problem with this code now is that even if there are multiple NPCs, just kill the NPCs, the crash like above occurs.
I left one NPC in the world now. But when the NPC’s stamina goes to zero, it suddenly crashes. What’s the problem?

For your information, it works fine when the player dies. Instead, the problem only happens when the player kills the NPC.

And I declared NPC as UPROPERTY. But when I check it with Unreal Engine, NPCs are fixed to 0, and the value does not change.

Please help me

[chrudimer]

Hi, the error message shows the call stack leading to the crash. So in your case the problem is in OLGameMode.cpp in line 35. So you very likely try to run something on a nullptr in that line.

From skipping through your code below, there is at least one issue that will lead to a crash. In the OLGameMode::DeadCheck if the Character is not a AOLCharacterPlayer but an AOLNPCBasic, the code will crash, since Player will be nullptr and you then later in the else if Character == NPC branch do: Player → GetController() which will crash since Player is a nullptr at that point.

[sehwa]

Thank you so much for your answer!! If the NPC dies as chrudimer says, the Player is null (because Character is coming over to the NPC)
I don’t have a clue how to write the code..

The language may not be natural because of the use of a translator.

[chrudimer]

For accessing the PlayerController, you could use

UGameplayStatics::GetPlayerController(GetWorld(), 0);

So in your code you would likely do:

AOLPlayerController* PlayerController = Cast<AOLPlayerController>(UGameplayStatics::GetPlayerController(GetWorld(), 0));

That way you do not need to access the player controller from the Character.

[sehwa]

Doing what chrudimer said made it really easy to get PlayerController. Thank you so much. I solved it thanks to you!
And thank you so much for telling me the problem with my code. It was an honor to learn!