what happens with uncaught exception

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Hi, just curious. Imagine my app throws some exception, e.g., throw "error";
-- if this is not caught anywhere, this will result in a crash in the end right?

Posted 12-Jun-13 20:59pm

Dan page

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3 solutions

Solution 3

If you don't catch the exception then it is unwinds even the main()/WinMain() call of your program and the exception gets caught by the runtime library that simply can not result in a happy end.

Posted 12-Jun-13 23:33pm

pasztorpisti

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Matthew Faithfull 13-Jun-13 6:24am

An interesting point. Does the MSVCRT runtime catch C++ exceptions or only Structured Exceptions? Source check needed to resolve that I think, I know it has an SEH catch(...) but I'm not convinced about C++ exceptions.

pasztorpisti 13-Jun-13 6:51am

In case of uncaught c++ exceptions the crt has to call your unexpected exception handler (if set). If you haven't set up your exception handler then the default behavior is calling terminate that calls the terminate handler. If you havent set up your terminate handler then the default behavior is calling abort().
http://www.cplusplus.com/reference/exception/set_unexpected/
http://www.cplusplus.com/reference/exception/set_terminate/

Personally my favorite solution to the problem is placing a generic exception handler at the root of the call tree. Handling exceptions/crashes per-thread is another challenge.

pasztorpisti 13-Jun-13 7:42am

With Visual Studio 2010 I couldn't get set_unexpected() work, but the fact that letting an exception to unroll main() still holds - it doesn't really matter whether the crt handles it or not.

Matthew Faithfull 13-Jun-13 8:54am

You're right of course. Thanks for the clarification and yes threads are a another issue.

The only time I can see where the CRT behaviour might matter is that if the CRT handles the exception then static variable destructors will be called. If it doesn't they won't.

pasztorpisti 13-Jun-13 11:29am

Static variable constructors are also interesting. If you load for example a DLL then the static ctors are executed before your LoadLibrary() call returns and DLL loading can fail silently/misteriously if you crash in your static ctors...

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Matthew Faithfull · Accepted Answer · 2013-06-12T23:18:00

Yes your program will crash but exactly how it will go out depends on a couple of things.
You're writing C++ but on what OS and with what framework?

For example on Windows some frameworks will install an unhandled exception filter for you and some won't.
Back in the day I don't think MFC did but now it may. This means you'll get a crash dialog that says you had an unhandled exception and may even give the user the opportunity to attempt to continue execution which is generally a bad idea. Otherwise the framework may give the user the opportunity to report the crash to the developer at this point which is possibly a good idea.
In most cases you can of course install your own unhandled exception filter overriding any provided for you. In all cases however you need to be sure of what will happen so you can protect the users data. The advice as ever is to know your enemy. :-)

CPallini · Accepted Answer · 2013-06-12T21:28:00

Solution 1

Yes, as you might easily verify yourself.

Posted 12-Jun-13 21:28pm

CPallini

Comments

Dan page 13-Jun-13 3:34am

I might verify it Once - which does not mean that will happen always, that is why I asked.

CPallini 13-Jun-13 3:51am

Well, computer programs behaviour is (usually :-) ) quite deterministic. However, if you need the comfort of the documentation, here you are:
http://msdn.microsoft.com/en-us/library/ac9f67ah(v=vs.110).aspx