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    <p><a href="http://msdn.microsoft.com/en-us/library/ms682583(v=VS.85).aspx" rel="nofollow noreferrer">The MSDN page for DllMain</a> has a quote that might help explain what is happening to you.</p> <blockquote> <p>When handling DLL_PROCESS_DETACH, a DLL should free resources such as heap memory only if the DLL is being unloaded dynamically (the lpReserved parameter is NULL). If the process is terminating (the lpvReserved parameter is non-NULL), all threads in the process except the current thread either have exited already or have been explicitly terminated by a call to the ExitProcess function, which might leave some process resources such as heaps in an inconsistent state. In this case, it is not safe for the DLL to clean up the resources. Instead, the DLL should allow the operating system to reclaim the memory.</p> </blockquote> <p>So if you are calling FreeLibrary it's essentially a clean shutdown. Everything is in a valid state still. Any threads the Dll created are still around. All its memory is still around.</p> <p>But if you just close the program (and don't call FreeLibrary) then it's more like an emergency shutdown (think crashing). Your Dll gets notified by the OS rather than the app. If this is the result of a crash then hoping memory is still valid isn't a great idea. And the stack is gone anyway.</p> <p>So my guess is you are running into this problem because non-freed libraries are unloaded differently.</p>
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    1. COWhat you are sayign is true but in my case its still not clear to me. i have added some details for ATTACH and DETACH case in the post. Please see, hope it helps my doubt. in DETACH case the case code gets executed irrespective whether OS is notifying the DETACH case or application itself. The thing is illegal memory access will happen in both situation.
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    2. COI just looked at your changes. Could you show me which line the access violation happens on? Although, even if you show me chances are my response will be "That object you are accessing is no longer in valid memory." (Obviously...that's what an access violation is) :D I read a great post about this a little while back: It boiled down to saving a shadow copy of your file (kind of like how Word does). That way if your app crashed or the power goes out things aren't lost. But more importantly, it lets you just crash. Things will be graceful by design. Hope this helps.
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    3. COButmy question still unanswered :) there is no difference in the code execution as i mentioned i did unmap and then tries to access the file mapped memory which is illegal. in case of FreeLibrary(), the next statement after accessing the memory location was not executed and silently program executed. in case of implicit call to DETACH, access violation error dialog box appears and then only i realized. So my point why the same dialog box was not appear in FreeLibrary() call. You cannot say that even after unmapping, the memory access is legal in that case :)
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