Re: How to check dll version?

From:

"Ben Voigt [C++ MVP]" <rbv@nospam.nospam>

Newsgroups:

microsoft.public.vc.language

Date:

Fri, 20 Jul 2007 22:58:00 -0500

Message-ID:

<53E61188-1A85-45EA-9CA5-E4F0BC37299E@microsoft.com>

"Alex Blekhman" <tkfx.REMOVE@yahoo.com> wrote in message
news:OPX6A7syHHA.5408@TK2MSFTNGP02.phx.gbl...

"bucher" wrote:
[...]

Now, if in main application, I only need to create an interface for every
dll. I don't have to write bunch of "GetProcAddess". If I want to add
more export functions, I should update the interface class. What I
worried about is if I use the old dll, main application will not report
any errors when call "CreateInstance". It will report an error when I
call the new function. Is there any method to check whether the dll is
consistent with the interface file?

I should warn you that exporting classes from DLL, besides the advantages
you mentiond, has following drawbacks:

1. Both DLL and its client must use C++.

2. Both DLL and its client must use the same version of the compiler in
order to be compatible. There is no binary compatibility for C++ code.

That's only true of __declspec(dllexport) on a class, which isn't being used
here. What the OP is trying to do is actually the correct way to avoid
dllexport'ed classes.

Regarding your versioning problem there is no ultimate solution. Usually,
once interface is published, it cannot change (like in COM). Interface is
a contract that you cannot breach unilaterally. If you need to add new
methods, then make new interface. For example,

class IHardwareInterface2
{
   // all methods from IHardwareInterface
   ...

   // new methods
   virtual DWORD NewMethod() = 0;
   ...
};

So, old clients will continue to use `IHardwareInterface' while new
clients will be aware of new functionality and use new interfaces.

Alex