Cheat Engine

[Estecka]

Hi,

I was only recently introduced to lua, so I might be missing something obvious.

I was working on some boilerplate lua script loop.
Because I've often caused some dramatic looping errors before, I wanted to set up some kind of catch-all error handler, that would abort the loop if anything goes wrong :

[TheyCallMeTim13]

I'd say it's just due to different error handling with in CE's code. I don't think pcall is setup to catch all errors it's more for catching lua errors not C level stuff. I'd say focus more on proper error handling and not trying to use a catch all. So have checks to make sure the value is of the right type and throw an error if it's not.

[Estecka]

Sure, type-checking will fix the issue right here and right now in this specific script, but that's it, and that's not quite what I'm looking for.
Writing a script that doesn't fail is good, but walking out of this with the assumption I'll never again write a script that fails in the exact same way (or any other way for that matter) would be presumptuous of me. I need that catch-all handler not to "fix" the error, but as a fail-safe, because the consequences for failure here are quite spectacular, and I want to attenuate them.

Aside, I'm thinking that if the only way to throw a proper error, is to wrap all value assignation with some type checking, maybe this check would deserve to be built into the setter for `MemoryRecord.value` ?

[TheyCallMeTim13]

When I said C level, I was making a generalisation. CE is written with pascal not Lua, thus when you set "SomeMemeoryRecord.Value" it's using pascal code to do that. It's just that the memory record object is exposed to lua.

And you can wrap an entire C# program in a try call, but any programmer worth their weight will tell you not to do anything like that and to work on proper error handling.

And it seems like the error is handled in pascal, that's why you get the invalid float error. But the pcall doesn't catch it and the timer keeps spamming the error. And you have the interval set to "16.6" milliseconds so it's spamming it fast and hard. And when I tested the code the "C stack overflow" didn't actually cause the lua to catch it either and it was that the whole script was stopped. But of course when you start talking stack overflow errors, I would expect odd behavior and for things to not always respond the same. Basically the call stack memory is being exceeded so the system kills whatever is causing it, thus the timer seems to stop. But the error message was never printed for me.

[Estecka]

The key difference between this and a regular C# program, is that any uncaught exception in a regular program would immediately kill the entire process, which is the best outcome we could hope for anyway. Here, this is not the case, the timer keeps running, doingspaghetti monsterknows what and spamming the error; ironically simply trying to replicate the usual behaviour of not having a try-catch block at the root of a program, requires here some kind of root try-catch.

Again, yes, proper error handling is preferable, but it only works after I've identified the errors that need to be handled. Until I know what kind of error I will need to handle or before I even realize there is an error I need to handle, this is the best I can get; and I can never be certain that all potential errors are being handled.

In any case, I've kept mulling it over, and here's a solution I came up with that should work with any error, catchable or not :

[ParkourPenguin]

There are Lua errors and there are pascal exceptions. It seems like the Lua environment doesn't care about pascal exceptions.

I guess you could try to acquire a critical section at the start of the loop and release it at the end if there aren't any errors. If you can't acquire it at the start, then it clearly wasn't released, and you can stop the timer early there.
(this is more or less what you're doing with UncaughtError)

I don't know what you're doing, but if pcall really seems like the best solution, you're probably doing something wrong. In all my experience with using Lua in CE, you really don't need to be handling errors like this. The only circumstance I can think of is if you're writing a library that uses some user-provided code as a callback or something. Even then, in most cases, it's fine to not use pcall.

This sounds stupid but the best error handling strategy really is to not generate errors in the first place. e.g. if you're assigning some numeric value to MemoryRecord.Value, make sure the string is a number first.

[Estecka]

[Dark Byte]

you can use a hybrid of lua and any other language.

e.g a plugin in c# and for gui access in CE use lua as a control interface