VC編譯ADO的開發環境和客戶環境的細微差別可能導致的失敗 (轉)

> The call to CreateInstance will fail when the code is
> compiled with a MDAC 2.7 version of msado.dll but run on
> a system with MDAC 2.5 installed. It returns a HRESULT of
> 0x80004002 (E_NOINTERFACE) - "The QueryInterface method
> did not recognize the requested interface. The interface
> is not supported.". i.e. the code tried to find the new
> _Command interface NOT the old _Command interface as
> defined in MDAC 2.5.
> The code works fine when compiled with MDAC 2.5 and run
> on a system with MDAC 2.5 or greater. (Will also work
> fine when compiled with MDAC 2.7 and run on MDAC 2.7).
>
> SOLUTIONS
> ------------------
>
> 1) Compile only on MDAC 2.5 and then can target MDAC 2.5
> or greater (Not really an option with (
> etc.))
>
> 2) Compile with MDAC 2.7 and force all clients to upgrade
> to MDAC 2.7 (Not an al solution as already have enough
> problems when forcing clients to install MDAC 2.5 -
> breaking existing apps - or simply not installing
> proy as part of the install process)
>
> 3) The solution we have come up with is to develop on
> systems with MDAC 2.7 installed but not to use
> the "_Command" interface. Instead we use the "Command25"
> interface (i.e. this is the renamed "_Command" interface
> from MDAC 2.5). This means all our developers are forced
> to develop on MDAC 2.7 but we can continue to target MDAC
> 2.5 or better). i.e. the above code becomes
>
> ADODB::Command25Ptr pCmdChange  = NULL;
> HRESULT hResult = pCmdChange.CreateInstance
> (__uuidof(ADODB::Command));