Handling exceptions thrown by ::load() method of QPluginLoader

I have 2 Qt plugins, main and helper, with main.dll loading helper.dll. I am able to successfully load main.dll with QPluingLoader when both main.dll and helper.dll are in the same folder. When helper.dll is absent and I try to load main.dll an exception gets thrown. That's understandable cause helper.dll cannot be found. My task is to successfully catch the thrown exception, rather than crashing the app. While debugging here is what Qt Creator displays:

The following code is not solving the problem, so I need to do something else...

std::exception_ptr eptr; QPluginLoader pluginLoader(packagePath); try {     pluginLoader.load(); } catch(...) {     eptr = std::current_exception(); } 

2 Answers

Answers 1

I believe in this case you should use the Windows __try / __except extensions:

__try  {    // guarded code } __except ( expression ) {    // exception handler code } 

This kind of exceptions will let you catch SEH errors, you can find a detailed article on MSDN about it: https://msdn.microsoft.com/en-us/library/swezty51.aspx

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Besides, but this is another topic, in order to terminate gracefully you could also use SetUnhandledExceptionFilter.

Answers 2

I have been able to resolve this. The problem was that my Qt application was not deploying itself (something that a Qt application has to do when it needs to be run independent from Qt creator. I added script to the .pro file of Qt Creator project. Once I did that, I do not see a crash, but a friendly error message generated by calling QPluginLoader::errrorString(), if the call to QPluginLoader::load() returns false.

Here is what my code looks like:

QPluginLoader pluginLoader(m_packagePath);  bool bLoaded = pluginLoader.load(); if (bLoaded) {     QObject* plugin = pluginLoader.instance();     m_metaObject = plugin->metaObject();     if (m_metaObject == nullptr)     {         qCritical() << "Unable to obtain entry class of input plugin. Please check your plugin.";         return false;     } } else {     qCritical() << "Message from Qt plugin loader:";     qCritical() << pluginLoader.errorString();     qCritical() << "Please make sure your input Qt plugin along with its dependencies are deployed with winqtdeploy.exe and in the same folder as your plugin.";     exit(-1); } 

I took the deployment script from another stackoverflow post which can be found here:

Automatic Copy of Dependent Files in Qt Creator

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