what to do if debug runs fine, but release crashes

Question

I have an application that runs just fine in the debug build, but when I start it in the release build, I get a

unhandled Exception at 0x0043b134 in myapp.exe: 0xC0000005:
Access violation while reading at position 0x004bd96c

If I click on 'break' it tells me that there are no symbols loaded and the source code can't be displayed.

What can I do in such a situation to track down the problem?

Answer 1

This kind of problem is often due to unitialized variables. I'd start there looking for your problem.

Debug mode is more forgiving because it is often configured to initialize variables that have not been explicitly initialized.

Perhaps you're deleting an unitialized pointer. In debug mode it works because pointer was nulled and delete ptr will be ok on NULL. On release it's some rubbish, then delete ptr will actually cause a problem.

Answer 2

It could be two things:

• One or more of your assertions does necessary work apart from the check itself
• Something else

To rule out the former, try redefining assert as an empty operation in the debug build. If the absence of some assertion causes the crash, you will see it. Otherwise, it's something else.

Also, I assume you have version control. Did this just start happening? You can analyze the code changes from last week.

Finally, even in the absence of a crash in debug mode, running a memory checker tool may be useful to spot incorrect memory access.