Function pointers in Unreal compared to standard C++. Getting an unexpected error which I cannot reproduce without UE4

I tried to reproduce this issue in a non Unreal Engine project, but I can’t seem to do it, so I’m quite unsure how to solve this, you can see how I [tried to reproduce it here.][1]

Anyhow, I’m trying to write a triggering gameplay system which works like this:

You have a trigger, can be anything, a volume trigger, a written button class which trigger something, a timed event or anything. That said trigger calls its trigger option class which only exists for the possibility of different usecases, some options at the top of my head: proxytrigger which instantly triggers, delayedtrigger which delays the trigger process, or something more complex like a trigger option that will only give you the OK sign if your health is 100%.

Once the TriggerOption tells the real Trigger that it’s been triggered, the TriggerAction will play, which can also be anything, a door opening perhaps? I wonder how many times I’ve said “trigger” by now … anyway, that’s the entire system. However, the process of TriggerOption telling TriggerActor (the actual trigger) that it should get triggered happens through a function pointer:

This is the function which sets up the function pointer:

void ATriggerActor::AttemptToTrigger()
	if (!TriggerOption)
		UE_LOG(LogTemp, Error, TEXT("TriggerOption is nullptr in TriggerActor: %s?"), *GetName());

	if (CanBeTriggered())
		TriggerOption->StartTriggerOption(this, &ATriggerActor::OnTriggerOptionCompletedCB);
		bHasBeenTriggered = true;

This is the function that calls it, or stores it or whatever this subclass wants to do with it, in this case, it just calls it.

void UTriggerOptionProxy::StartTriggerOption(ATriggerActor* CallbackOwner, VoidFuncPtrNoParams CompletionCB)
	(CallbackOwner->* (CompletionCB))();

This is also the typdef for the function pointer btw: typedef void(ATriggerActor::*VoidFuncPtrNoParams)(void);

When trying to call the function pointer,

, it throws this:

Exception thrown at 0x00007FF8A0954197 (UE4Editor-UE4Systems-3138.dll) in UE4Editor.exe: 0xC0000005: Access violation reading location 0xFFFFFFFFFFFFFFFF.

EDIT: Trying to fix the code format…


Im not sure i understod fully what you want, but seems to me you try to overthink this a little bit :slight_smile:

What about delegates, timers, events, interfaces? :slight_smile:
Technically all of this things is designed to trigger functions at some point and they implemented properly so you can use it freely…

I know this is not what you asked, but maybe a good advice :wink:
but if you wanna go with function pointers, maybe this wiki helps: A new, community-hosted Unreal Engine Wiki - Announcements - Unreal Engine Forums