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Important This document may not represent best practices for current development, links to downloads and other resources may no longer be valid. Current recommended version can be found here.

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);
}

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