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How to: Define and Install a Global Exception Handler

The following code example demonstrates how unhandled exceptions can be captured. The example form contains a button that, when pressed, performs a null reference, causing an exception to be thrown. This functionality represents a typical code failure. The resulting exception is caught by the application-wide exception handler installed by the main function.

This is accomplished by binding a delegate to the ThreadException event. In this case, subsequent exceptions are then sent to the App::OnUnhandled method.

Example

// global_exception_handler.cpp
// compile with: /c /clr
#using <system.dll>
#using <system.drawing.dll>
#using <system.windows.forms.dll>

using namespace System;
using namespace System::Threading;
using namespace System::Drawing;
using namespace System::Windows::Forms;

ref class MyForm : public Form
{
   Button^ b;
public:
   MyForm( )
   {
      b = gcnew Button( );
      b->Text = "Do Null Access";
      b->Size = Drawing::Size(150, 30);
      b->Click += gcnew EventHandler(this, &MyForm::OnClick);
      Controls->Add(b);
   }
   void OnClick(Object^ sender, EventArgs^ args) 
   {
      // do something illegal, like call through a null pointer...
      Object^ o = nullptr;
      o->ToString( );      
   }
};

ref class App
{
public:
   static void OnUnhandled(Object^ sender, ThreadExceptionEventArgs^ e)
   {
      MessageBox::Show(e->Exception->Message, "Global Exeception");
      Application::ExitThread( );
   }
};

int main()
{
   Application::ThreadException += gcnew 
      ThreadExceptionEventHandler(App::OnUnhandled);

   MyForm^ form = gcnew MyForm( );
   Application::Run(form);
}

See Also

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