How to Properly Register a CPP DLL into COM Using Wix MSI Installer?

Registering a CPP dll into COM after installation using Wix Msi installer

Short, Summary Answer

You need to stop using batch files and custom actions for COM registration (unreliable) and rather extract the COM registration information using the heat.exe tool from the WiX toolkit to add the COM registration to your MSI database at compile time.

There are some complications for 64-bit binaries, see details below. Fortunately it looks like you are dealing with a 32-bit component based on your installation directory shown above.

In this particular case it helped to run heat.exe on the COM file after deployment when all dependencies were "in place" for the COM file to load properly. There is a lot of "debugging communication" in these answers - I'll leave it all in place for the future, but try this simple solution first. And perhaps try the new dependency tool "Dependencies.exe" described below.

Long, Detailed Answer

Before I try to answer the question (which seems to revolve around missing dependencies or something weird being done in your batch file), I want to clear up a few things for you with regards to best practice for COM registration.

Self-registration Considered Harmful

Self-registration should not be used to register COM files. Here is a description of why this is the case: [MSI register dll - Self-Registration considered harmful](https://stackoverflow.com/questions/2736641/com-registration-where-did-the-idea-of-no-self-registration-come-from/2737548#2737548). There is good news, however, doing things as intended via built-in MSI mechanisms will be both easier and more reliable once you set it up properly.

Rather than using custom actions or the SelfReg table, COM registration information should be extracted from your COM files at compilation time - in other words when you compile your MSI file from your WiX source files. The extracted registry data should be used to populate the family of MSI data tables designed to reliably register and unregister the COM file during installation and uninstallation respectively.

WiX: The "heat.exe" Command Line Tool

Understanding the intricate details of this process is not necessary - all you need to know is what tools to use. WiX provides the "heat.exe" tool for this purpose. It is essentially a "harvester" tool capable of generating valid WiX XML source files for several purposes - one of which is COM extraction. It also supports traversing directories in general - generating WiX source files which can install the files encountered during traversal. It is essentially a very quick way to make an MSI package once you know how to use it.

Dependency Walker

So we have established that you should take the time to learn how to use heat.exe to generate the WiX source necessary to register the COM file properly. however, there is one more problem: the missing dependencies.

For a COM file to be able to self-register - or for you to be able to successfully extract the COM registry data using heat.exe - the COM file must be able to load correctly. For this to be possible all dll dependencies must be available on the system in question in an accessible location.

Get yourself a copy of Dependency Walker and use it to scan your COM file for what files it depends on. Here is an example of a COM file which fails to load because it cannot find MMUtilities.dll:

[Image of Dependency Walker output showing missing dependency]

You will most likely find something similar wrong with your dll (or whatever file type it is, for example OCX) when it is run from your setup's installation location. The required dependency files can not be found by regsvr32.exe and the registration process fails.

There are some reported missing dependencies that are not important - I guess this has to do with the age of the Dependency Walker tool - it hasn't been updated recently as far as I know. Look for a file you recognize as either your own dependency file or a core system file as opposed to very long dll names of files you have never heard of. Keep in mind that some dlls have dependency language dlls that are required for loading. For example MMUtilities.dll needs MmUtilitiesEnglish.dll or another language dll present in the same folder to be able to load correctly.

Some sample false positive dependencies for the above file: API-MS-WIN-CORE-RTLSUPPORT-L1-1-0.DLL, API-MS-WIN-CORE-PROCESSTHREADS-L1-1-0.DLL, API-MS-WIN-CORE-REGISTRY-L1-1-0.DLL, etc... There were many. I believe, but I am not sure, that the root cause of these false positives centers around problems with side-by-side components installed to the

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