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FindFunctionByName() is returning a UFunction* with an invalid Func pointer?

Hey gang! Got a strange issue and we can't seem to pinpoint the cause. Hopefully you have seen/solved this one?

We have a native base class that implements an event OnFoo(). This class is the parent of multiple native subclasses. Multiple blueprint classes have been derived from the native subclasses, and each of them implements OnFoo() within its Graph in precisely the same way. At runtime using a cooked build, when OnFoo() is called, one - and always the same one - of the blueprint classes crashes the game with the nondescript "Fatal error!" message. The crash does not occur in PIE.

Further investigation reveals that when this specific blueprint calls OnFoo(), its class does have "OnFoo" in its FuncMap, but the Func pointer is null. The Engine doesn't currently validate the Func pointer prior to invocation, which causes the crash. (We've since added defensive code inside UClass::FindFunctionByName() to validate Func, and when it fails we continue past, traversing up the Super Class chain until we find a valid match.) Again, this issue seems isolated to only one of the blueprint classes; all the other sibling blueprints contain valid Func pointers inside their FuncMaps.

The question is ultimately, what would cause OnFoo() to be added to this blueprint's FuncMap without a valid Func?

Product Version: UE 4.9
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asked Sep 22 '15 at 11:01 PM in C++ Programming

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Brian Fox
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