MDAC 2.5 SDK - OLE DB Providers
OLE DB Provider for SQL Server
COM objects report errors through the HRESULT return code of object member functions. A COM HRESULT is a bit-packed structure. COM provides macros that dereference structure members.
COM specifies the IErrorInfo interface. The interface exposes methods such as GetDescription, allowing clients to extract error detail from COM servers. OLE DB extends IErrorInfo to support the return of multiple error information packets on a single-member function execution.
SQLOLEDB exposes the OLE DB record–enhanced IErrorInfo, the custom ISQLErrorInfo, and the provider-specific ISQLServerErrorInfo error object interfaces.