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POWin32 Message Handler Error Propagation
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copied!<p>I'm writing a (C++) application that utilizes a single dialog box. After setting up a message pump and handler I started wondering how I would go about propagating C++ exceptions to my original code (i.e., the code that calls <code>CreateDialogParam</code>, for instance).</p> <p>Here's a skeleton example of what I mean:</p> <pre><code>BOOL CALLBACK DialogProc(HWND, UINT msg, WPARAM, LPARAM) { if(msg == WM_INITDIALOG) //Or some other message { /* Load some critical resource(s) here. For instnace: const HANDLE someResource = LoadImage(...); if(someResource == NULL) { ---> throw std::runtime_error("Exception 1"); <--- The exception handler in WinMain will never see this! Maybe PostMessage(MY_CUSTOM_ERROR_MSG)? } */ return TRUE; } return FALSE; } //====================== void RunApp() { const HWND dlg = CreateDialog(...); //Using DialogProc if(dlg == NULL) { throw std::runtime_error("Exception 2"); //Ok, WinMain will see this. } MSG msg = {}; BOOL result = 0; while((result = GetMessage(&msg, ...)) != 0) { if(result == -1) { throw std::runtime_error("Exception 3"); //Ok, WinMain will see this. } //Maybe check msg.message == MY_CUSTOM_ERROR_MSG and throw from here? TranslateMessage(&msg); DispatchMessage(&msg); } } //====================== int WINAPI WinMain(...) { try { RunApp(); //Some other init routines go here as well. } catch(const std::exception& e) { //log the error return 1; } catch(...) { //log the error return 1; } return 0; } </code></pre> <p>As you can see, <code>WinMain</code> will handle "Exception 2" and "3", but <strong>not</strong> "Exception 1".</p> <p><strong>My fundemental question is simple; what would be an elegant way to propagate these sorts of errors to the original "calling" code?</strong> </p> <p>I thought of maybe using custom messages and moving the actual <code>throw</code>-statements out to the message pump (in <code>RunApp()</code>), but I'm not sure how that would work yet as I have relatively little experience with Windows in general.</p> <p>Perhaps I'm looking at this situation all wrong. How do <em>you</em> usually bail out when something fatal (i.e., an acquisition of a critical resource fails, and there's no chance for recovery) when you're in the message handler?</p>

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