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Editorial Team
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Asked: 2026-06-18T03:14:54+00:00

Is it possible that luabind checks, if a member function call to an exported

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Is it possible that luabind checks, if a member function call to an exported class (object) is for a valid object?

lets assume that i have a Class called Actor exposed using luabind to lua. Im calling a lua function from C++ with an actor object as parameter. Now before the function finishes, a script write would put the actor object in a global lua reference to be accessed later.

Later on, the actor object is deleted from the C++ site, another function is called which tries to access the invalidated actor object (any method from it) – and obviously since it has been deleted, it results in a crash (access violation)

sample:

local myObjRef = nil

function doSomethingWithActor(actor)
 -- save, still valid object
 actor:Say("hello")
 myObjRef = actor
end

function calledAfterActorWasDeleted()
  --- will crash if the c++ object has been deleted meanwhile, works fine if it still exists
  myObjRef:Say("Crash...")
end

A NIL check doesnt help here, is this something that can be checked on luabinds site? The functions are executed using lua_pcall(….) and the stacktrace shows the error at luabinds call.hpp results = maybe_yield(L, lua_gettop(L) – arguments, (Policies*)0);

If not, is there another solution how to make sure somebody who writes a script cannot create these issues?

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1 Answer

  1. Editorial Team

    I solved my issue the following way:

    When im about to delete an object, i iterate through all lua functions from C++ (i have them in a list, they are bound to specific actor objects each). Then i inspect each upvalue (global/local vars accessable to a function) – then i compare the userdata pointer with my object im about to delete – if they match (and their classes) and NIL the upvalue. Optionally, i could just remove that offending function because it would not work well anymore anyway.

    So the next the time the function is called, im just getting a soft lua error “trying to access xxx a nil value…” – no more access violations.

    I know people would say “dont use lua_getupvalue/lua_setupvalue – they are only for debugging!” – but there is actually no documented or spoken side effect – and in my case its perfectly safe and works well – also there isnt the issue with left over proxy objects i could not delete.

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