VS2008 Debugger does not break on unhandled exception

Question

I\'m having an odd problem with my vs debugger. When running my program under the vs debugger, the debugger does not break on an unhandled exception. Instead control is re

Answer 1

Ctl-D, E brings up the Exceptions window. You can set what exceptions you want to, and don't want to, break on.

Answer 2

Once every while this happens to me as well. It seems like a bug or something, as when I replicate the scenario the exception is caught and shown as usual.

Answer 3

If you're on a 64-bit OS, there's a pretty good chance you're being bitten by an OS-level behavior that causes exceptions to disappear. The most reliable way to reproduce it is to make a new WinForm application that simply throws an exception in OnLoad; it will appear to not get thrown. Take a look at these:

1. Visual Studio doesn't break on unhandled exception with windows 64-bit
   • http: // social.msdn.microsoft.com/Forums/en/vsdebug/thread/69a0b831-7782-4bd9-b910-25c85f18bceb
2. The case of the disappearing OnLoad exception
3. Silent exceptions on x64 development machines (Microsoft Connect)
   • https: // connect.microsoft.com/VisualStudio/feedback/details/357311/silent-exceptions-on-x64-development-machines

The first is what I found from Google (after this thread didn't help), and that thread led me to the following two. The second has the best explanation, and the third is the Microsoft bug/ticket (that re-affirms that this is "by design" behavior).

So, basically, if your application throws an Exception that hits a kernel-mode boundary on its way back up the stack, it gets blocked at that boundary. And the Windows team decided the best way to deal with it was to pretend the exception was handled; execution continues as if everything completed normally.

Oh, and this happens everywhere. Debug versus Release is irrelevant. .Net vs C++ is irrelevant. This is OS-level behavior.

Imagine you have to write some critical data to disk, but it fails on the wrong side of a kernal-mode boundary. Other code tries to use it later and, if you're lucky, you detect something's wrong with the data ...but why? I bet you never consider that your application failed to write the data---because you expected an exception would be thrown.

Jerks.

Answer 4

There are two checkboxes in the "Exceptions..." box, I usually have to have them both checked to get it to break on unhandled exceptions. Regardless that it only reads like you need to have one checked.

Answer 5

I had a similar problem, and checking "Enable Just My Code (Managed Only)" fixed the problem, while if I turned it back off then the problem came back, no clue why (but it is possible that some DLL's that appear to get loaded when it is unchecked cause the behavior).

Answer 6

When I read the answer about having two check boxes in the "Exception..." dialog, I went back and opened the dialog again. I only had one column of check boxes -- for break on "Thrown".

As it turns out, if you do not have "Enable Just My Code (Managed Only)" checked in the Debug options, the "User-Unhandled" column does not show in the "Exceptions" dialog.

I selected the "Enable Just My Code" option and verified that the "User-unhandled" checkbox on the "Exceptions" dialog was selected for all of the exception categories.

I was able to get unhandled exceptions to break into the debugger for one session. But when I came back the next day, the behavior was as before.

Metro.