Code running weirdly, jumping everywhere

Development World Creation
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1

Hello everyone, I have a bit of a problem…

I recently started coding in UE4 and I saw some weird behaviour.
I’m trying to get tracing to work, so to get to the point:
In the Visual Studio Debugger I put a breakpoint before an if statement, but the code ran even when the parameter was false, then it proceeded to jump in and out of the statement.

void UVehicle_MovementComp::Trace()
{
	for (int i = 0; i < tracerPoints.Num(); i++)
	{
		//gets weird here:
		if (tracerPoints[i]->tag.Compare(FString(TEXT("Predictable"))) == 0)
		{
			bool hit = World->LineTraceSingleByObjectType(
			traceHits[i], 
			tracerPoints[i]->startPoint, 
			tracerPoints[i]->endPoint, 
			FCollisionObjectQueryParams::AllObjects, 
			traceParams);
			//in this instance this is false, 
			//but it goes inside anyway
			if (hit)
			{
				//this is even weirder:
				//this runs, then jumps out,
				//then it runs again,
				//then it jumps inside the 
				//outer else branch
				FString str = 
					TEXT("ID:") + 
					FString::FromInt(i) + 
					TEXT(" - RayTrace Hit! ") + 
					FString::SanitizeFloat(traceHits[i].Distance);
				//this never runs, as it shouldn't,
				//because it shouldn't even get this far
				if (IsValid(traceHits[i].GetActor()))
					str.Append(
						TEXT(" (") + 
						traceHits[i].GetActor()->GetName() + 
						TEXT(")"));
				if (IsValid(traceHits[i].GetComponent()))
					str.Append(
						TEXT(" (") + 
						traceHits[i].GetComponent()->GetName() + 
						TEXT(")"));
				GEngine->AddOnScreenDebugMessage(
					-1, 
					0.015f, 
					FColor::Green, 
					str);
			}
			//this never runs:
			else
			{
				traceHits[i].Reset(1, false);
			}
		}
		else
		{
			//it continues here, runs this line,
			//freaks out, then jumps to the end
			//(No breaks or warnings)
			bool hit = World->LineTraceSingleByObjectType(
			traceHits[i], 
			tracerPoints[i]->startPoint, 
			tracerPoints[i]->endPoint, 
			FCollisionObjectQueryParams::AllObjects, 
			traceParams);
			if (hit)
			{
				FString str = 
					TEXT("ID:") + 
					FString::FromInt(i) + 
					TEXT(" - RayTrace Hit! ") + 
					FString::SanitizeFloat(traceHits[i].Distance);
				if (IsValid(traceHits[i].GetActor()))
					str.Append(
						TEXT(" (") + 
						traceHits[i].GetActor()->GetName() + 
						TEXT(")"));
				if (IsValid(traceHits[i].GetComponent()))
					str.Append(
						TEXT(" (") + 
						traceHits[i].GetComponent()->GetName() + 
						TEXT(")"));
				GEngine->AddOnScreenDebugMessage(
					-1, 
					0.015f, 
					FColor::Yellow, 
					str);
			}
			else
			{
				traceHits[i].Reset(1, false);
			}
		}
	}
}

If you need any more info, I’ll gladly help.
Thanks

Edit:Here’s part of the header file:

struct TracePoints{
	FVector startPoint;
	FVector endPoint;
	FString tag;

	TracePoints(FVector start = FVector::ZeroVector, 
	FVector end = FVector::ZeroVector, 
	FString tag = TEXT("")) :
		startPoint(start), endPoint(end), tag(tag) {}
};

UCLASS()
class AEROX_API UVehicle_MovementComp : public UPawnMovementComponent
{
	GENERATED_BODY()
	
private:

	TArray<AActor*> tracerIgnoredObjects;

	TArray<TracePoints*> tracerPoints;

	FCollisionQueryParams traceParams = FCollisionQueryParams(true);

	TArray<FHitResult> traceHits;

	USkeletalMeshComponent* parentMesh;

	void Trace();

protected:
	//Init
	virtual void InitializeComponent() override;

	//Tick
	virtual void TickComponent(
	float DeltaTime, 
	enum ELevelTick TickType, 
	FActorComponentTickFunction *ThisTickFunction) override;

}
2

Are you building in debug? If not, the compiler has probably rearranged code on you for optimization reasons. You can’t really trust single stepping through optimized code.

3

That was indeed the problem! Thank you for the help :slight_smile: Now to investigate why the trace returns false, while there is a cube it’s hitting…