UE4 crashes when calling Add on a TArray ('UE4Editor_Core!rml::internal::reallocAligned()')

Development Programming & Scripting C++
10

Yeah, it’s valid, but I think I know where the problem is.

The problem occurs on RegisterPassive, when this is called:



targetAttribute->RegisterPassive(this);

But I thought that targetAttribute was valid, and it seems it isn’t. Here’s the code I omitted from UBasicPassive::OnInitialize (I thought it wasn’t relevant for this post)



void UBasicPassive::OnInitialize()
{
    Super::OnInitialize();

    targetEntity = Cast<ABaseEntity>(target->GetOwner());

    if (UProperty* prop = targetClass->FindPropertyByName(targetAttributeName))
    {
        targetAttribute = (UEntityAttribute*)prop->ContainerPtrToValuePtr<UObject>(targetEntity);

        if (targetAttribute == nullptr)
        {
            //Log Error
            return;
        }
    }
    else
    {
        //Log Error
        return;
    }

    targetAttribute->RegisterPassive(this);
}

As you can see, targetAttribute is never null, but it doesn’t mean the pointer is valid. So when I call RegisterPassive, I’m calling it on an invalid object and everything goes to hell. After I did a Cast instead of a C-Style cast, UE4 crashed because the pointer returned by [FONT=courier new]prop->ContainerPtrToValuePtr(targetEntity) wasn’t a [FONT=courier new]UEntityAttribute.

After finding this I could fix the problem, here’s how I get [FONT=courier new]targetAttribute now



if (UObjectProperty* prop = Cast<UObjectProperty>(targetClass->FindPropertyByName(targetAttributeName)))
{
    targetAttribute = Cast<UEntityAttribute>(prop->GetObjectPropertyValue_InContainer(targetEntity, 0));
...

Now everything works fine. The issue was caused because the C-Style cast can only fail at compile-time, so if the object isn’t a [FONT=courier new]UEntityAttribute I get no errors but the pointer is invalid.

Ok, lesson learned, always prefer UE4’s Cast function or C++ casts (dynamic_cast, static_cast) over C-Style casting.

Thanks for your help!

(■■■■ I feel stupid)