Question

I’m working on a piece of C++ software which runs on all Windows versions between Windows XP and Windows Vista. In my code, I developed a DLL which links against a standard library (the Qt library). Once my software is deployed, it’s not unusual that the user doesn’t have the exact same Qt build on his system but a slightly different configuration. There might be features disabled (so their Qt build doesn’t export the same set of symbols) or the library might even be changed in ways which make the library binary incompatible to the original.

At some point, I’m loading my DLL via a LoadLibrary() call. This pulls in whatever Qt library is on the user’s system. If I’m lucky, their Qt build is compatible with what I used while developing my DLLs, so LoadLibrary() succeeds. However, depending on the changes they did to their Qt build, the LoadLibrary() call sometimes fails with

• “The specified Module could not be found.”; this usually happens if their Qt build consists of less DLLs than my Qt build. So my DLL attempts to load e.g. QtFoo.dll but since this dll is not part of their Qt build, loading my DLL fails.
• “The specified Procedure could not be found.”; this usually happens if they changes their Qt build so that certain features are disabled, which results in less exported symbols.

My question is: how can I catch these errors gracefully? Right I’m simply using GetLastError() and then print either of the above two messages. However, it would be much more useful if I knew which module could not be found, or which procedure is missing. I noticed that when running an application in the explorer which links against a missing DLL, explorer manages to yield a nice ‘The application foo could not be loaded since the required library blah.dll is missing’. Is there maybe some API available to get more information about why a LoadLibrary() call failed exactly?

Answer 1

Can MapAndLoad from ImageHLP.DLL may help. It returns a LOADED_IMAGE structure.