PRB: Parameter that Takes a Reference to a String Does Not Change After Failed Call to Unmanaged Method (317533)

MORE INFORMATION

Steps to Reproduce the Behavior

1. Create an unmanaged COM server with one method that has the following implementation:

   //IDL
   [id(1), helpstring("method GetName")] HRESULT GetName([in,out] BSTR *str);
   					

   //Method implementation.
   STDMETHODIMP CEmployee::GetName(BSTR *str)
   {
         *str = ::SysAllocString(L"Test Name");
   
          //Fail here for testing.
          return E_FAIL;
   }
   					

2. Call this method from a managed client, as follows:

   EmployeeClass obj = new EmployeeClass();
   string empName="No Name";
   obj.GetName(ref empName);
   					

When you call the method, the method generates an exception error because of the failed E_FAIL HRESULT. If you break the program and examine the content of empName, you find that it is not changed. You can see similar behavior if you use the System.Text.StringBuilder class instead of the System.String class. To use the System.Text.StringBuilder class, change the Microsoft intermediate language (MSIL), and then rebuild the runtime callable wrapper.