Run two versions of the same unmanaged dll (referenced by C#-app)

Question

Background

I have two softwares, written in C#, using the same third-party dll to get telephony-capabilities.

Problem

When I deploy a new version of one of these softwares, I also deploy a new version of the dll. This one overwrites the references to the older dll, causing my other software to stop working, since the new dll isn't backwards compatible.

Attempted solutions

• Deploy the new software with a registration-free version of the dll.
  This doesn't work since the dll doesn't have a strong name. Result from sn:

C:\Program Files (x86)\Microsoft SDKs\Windows\v8.0A\bin\NETFX 4.0 Tools>sn.exe -e "theDll.dll" key

Microsoft (R) .NET Framework Strong Name Utility Version 4.0.30319.17929 Copyright (c) Microsoft Corporation. All rights reserved.

theDll.dll does not represent a strongly named assembly

• Ask the vendor for a strongly named version

This resulted in a "huh?". The dll works well however, so I don't want to look for a new vendor if I dont really have to.

• Give the dll a strong name using ildasm:

C:\Program Files (x86)\Microsoft SDKs\Windows\v8.0A\bin\NETFX 4.0 Tools>ildasm.exe "theDll.dll" /out=theDll.il

error : 'theDll.dll' has no valid CLR header and cannot be disassembled

Which seems to imply that the dll is unmanaged, and thus not possible to strongly name (if I'm not mistaken).

• Use SetDllDirectory and LoadLibrary to load the correct version of the dll.
  This seems to kinda work, at least I can load the correct dll from a specified place without registering it. This seems like a rather involved way to do it though.

Questions

• Has anyone done this the "LoadLibrary"-way and can verify that it works well for a dll where you need to instantiate some classes?

• Does anyone have a better solution?

Answer 1

This instruction told me how to construct an appropriate manifest file for an unmanaged COM: https://msdn.microsoft.com/en-us/library/ms973913.aspx

A few important points I don't feel they covered so that I easily understood:

• Oleview.exe is one way of getting the info you'll need for the manifest. It is possible to find your dll both by using Object classes-> All objects (provided it is registered with regsvr32) or by using File-> View TypeLib. I felt both these were needed before I had all information (they display different information).

• When you have your manifest file, it is sufficient to chose "Add reference" in Visual studio, selecting the "Browse"-tag and then the COM-manifest you created. After that, programming is exactly as if the COM had been registered. VS will create the manifest for your program.

• Of course you'll need to make sure your setup project deploys the .dll and its manifest to the same folder as your .exe.