Make the CCoInitializer constructor exception safe

[isnullxbh]

The source code example is accompanied by the following comment:

// An exception-safe wrapper class that manages the lifetime
// of the COM library in a given scope.

, but the CCoInitializer constructor throws an exception when the CoInitializeEx call completes with an error:

// Initialize the COM library on the current thread.
HRESULT hr = CoInitializeEx(NULL, dwCoInit);
if (FAILED(hr))
   throw hr;

I thought it may be a mistake in the comment, but the example below says otherwise:

int wmain()
{
   HRESULT hr;

   // Enable COM on this thread for the lifetime of the program.   
   CCoInitializer coinit(COINIT_MULTITHREADED);
   // Code
}

There is no try/catch block that encloses the creation of the CCoInitializer class instance.

The CCoInitializer implementation also indicates that the constructor shouldn't throw an exception:

explicit CCoInitializer(DWORD dwCoInit = COINIT_APARTMENTTHREADED)
   : _coinitialized(false)
{
   // Initialize the COM library on the current thread.
   HRESULT hr = CoInitializeEx(NULL, dwCoInit);
   if (FAILED(hr))
      throw hr;
   _coinitialized = true;
}

, otherwise, the usage of the _coinitialized flag is redundant - if an exception will be thrown at the constructor call, the destructor will never be called, so the _coinitialized flag will never be used.

[colin-home]

@isnullxbh
Thanks for the contribution. I think you're right about the intent with exceptions. I tweaked the edit a bit to cover the already-initialized case (which is almost certainly a sign the calling code has a bug, but keeps it from failing).