Can I use two incompatible versions of the same DLL in the same process?

Question

I\'m using two commercial libraries that are produced by the same vendor, called VendorLibA and VendorLibB. The libraries are distributed as many DLLs that depend on the com

Answer 1

As someone else mentioned, you could rename one of the copies of VendorLibUtils and modify the import table of the associated VendorLib DLL to link to it, rather than the VendorLibUtils.dll it was created with.

There's a few tools out there that let you edit EXE/DLL files in this way. CFF Explorer is a pretty decent one which allows editing of the import table. If you open up the VendorLib DLL in it and go to the Import Directory section (in the tree on the left), you'll see a list of modules at the top of the main window. You can rename the module by double-clicking on its name. Then you just save the DLL and it should now use your renamed VendorLibUtils DLL.

Of course, this assumes that VendorLib uses the import table to access VendorLibUtils, which it may not -- it may use LoadLibrary/GetProcAddress, in which case you won't see an import table entry for VendorLibUtils.

Actually, if the VendorLib does use the import table but also uses LoadLibrary to access the VendorLibUtils DLL in some places (I've seen it done), those places will still use the wrong one. If you rename both libraries, you might at least see an error if this is the case (since a DLL with the original name won't exist now). There is a way to deal with this if it occurs, but it starts to get quite complicated at this point, so I won't elaborate unless you really want/need to know.