Pass value by reference

Development Programming & Scripting C++
1

I don’t understand why this line gives error C4239, something about non standard conversion from FVector to FVector& for RandomPt. I’m learning c++ I have no idea what is wrong please help

offending line

FVector RandomPt;
bool bFound = GetRandomPointInRadius(Bot->GetActorLocation(), SearchRadius, RandomPt);

and this is the funcion

bool AAIEnemy::GetRandomPointInRadius(FVector& Origin, float Radius, FVector& OutResult)
{	
	UNavigationSystemV1* NavSys = FNavigationSystem::GetCurrent<UNavigationSystemV1>(this);

	if (!NavSys)
	{
		return false;
	}
	
	FVector Result;
	bool bSuccess = NavSys->K2_GetRandomReachablePointInRadius(GetWorld(), Origin, Result, Radius);

	//Out
	OutResult = Result;
	return bSuccess;
}

Can you find what’s wrong?

2

You probably just want to use your OutResult as the out Result in your call to K2_GetRandom…

bool AAIEnemy::GetRandomPointInRadius(FVector& Origin, float Radius, FVector& OutResult)
{	
	UNavigationSystemV1* NavSys = FNavigationSystem::GetCurrent<UNavigationSystemV1>(this);

	if (!NavSys)
	{
		return false;
	}

        return 	NavSys->K2_GetRandomReachablePointInRadius(GetWorld(), Origin, OutResult, Radius);
}

… if you wanted to assign like you did above, i think you’d need to assign as a pointer, ie “OutResult = *Result;” … or is it “OutResult = &Result;” … one of those. my pointer operations never make sense when i’m running on no sleep.

3

Ty. I’ll check the function, but I get the error only when I call it

FVector RandomPt;
bool bFound = GetRandomPointInRadius(Bot->GetActorLocation(), SearchRadius, RandomPt);

AIEnemy.cpp(76) : error C4239: nonstandard extension used: 'argument': conversion from 'FVector' to 'FVector &'

checking on the web I find that when this error happens, the argument must be passed as constant

bool AAIEnemy::GetRandomPointInRadius(FVector& Origin, float Radius, const FVector& OutResult)
{
	...
}

but I don’t get it. What’s the point in passing a constant variable by reference if I’ll not be able to modify it, which is exactly what I’m trying to do? This doesn’t make any sense lol sorry for my ignorance.

4

The problem here is that GetActorLocation() returns an FVector by value, which you cannot directly pass to a mutable reference. Update your function to use const FVector& Origin.

1 Like
5

That was the problem, I would never have found it by myself. Thanks a lot.