FIX: dbDao's CdbException Uses Private Constructor

The information in this article applies to:

• The DAO C++ Class Library included with: The DAO Software Development Kit (SDK), version 3.0

SYMPTOMS

It is difficult to explicitly throw a CdbException from the dbDAO class library. It is possible, depending on how the exception class is thrown, to generate this error:

   C2248: 'CdbException::CdbException' : cannot access private member
   declared in class 'CdbException'

CAUSE

This is because the constructor for the class is implicitly private. It does not inherit, nor are any classes inherited from CdbException, and it does not define any friends for the class.

The dbDao classes, however, are successfully able to throw the exception, but only because of another bug within the Visual C++ 4.0 compiler that allows you to throw a temporary instance of a class with only a private constructor.

RESOLUTION

The error is generated if you declare an instance of CdbException and then attempt to throw it.

   HRESULT hr;
   CdbException myException( hr );
   throw myException;          // Generates error C2248

   HRESULT hr;
   throw CdbException( hr );

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug was corrected in Visual C++ 32- bit Edition version 4.1.