.net – Gacutil.exe successfully adds assembly, but assembly not viewable in explorer. Why

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I'm running GacUtil.exe from within Visual Studio Command Prompt 2010 to register a dll (CatalogPromotion.dll) to the GAC. After running the utility, it says Assembly Successfully added to the cache, and running gacutil /l CatalogPromotionDll shows that the GAC contains the assembly, but I can't see the assembly when I navigate to C:\WINDOWS\assembly from Windows Explorer. Why can't I see the assembly in WINDOWS\assembly from Windows Explorer but I can see it using gacutil.exe?

Background: Here's what I typed into the command prompt for VS Tools:


    C:\_Dev Projects\VS Projects\bmccormack\CatalogPromotion\CatalogPromotionDll\bin
    \Debug>gacutil /i CatalogPromotionDll.dll
    Microsoft (R) .NET Global Assembly Cache Utility.  Version 4.0.30319.1
    Copyright (c) Microsoft Corporation.  All rights reserved.

    Assembly successfully added to the cache

    C:\_Dev Projects\VS Projects\bmccormack\CatalogPromotion\CatalogPromotionDll\bin
    \Debug>gacutil /l CatalogPromotionDll
    Microsoft (R) .NET Global Assembly Cache Utility.  Version 4.0.30319.1
    Copyright (c) Microsoft Corporation.  All rights reserved.

    The Global Assembly Cache contains the following assemblies:
      CatalogPromotionDll, Version=1.0.0.0, Culture=neutral, PublicKeyToken=9188a175
    f199de4a, processorArchitecture=MSIL

    Number of items = 1

However, the assembly doesn't show up in C:\WINDOWS\assembly.

Best Answer

That's because you use the .NET 4.0 version of gacutil.exe. It stores the assembly in a different GAC, the one in c:\windows\microsoft.net\assembly. Where all .NET 4.0 assemblies are stored. There is no shell extension handler for that one, the folders are visible as-is. You can have a look-see with Windows Explorer, .you'll see the internal structure of the GAC folders. You shouldn't have any trouble finding your assembly back, the GAC isn't particularly complicated.

If the assembly is intended to be used by an app that targets an earlier version of .NET then you should use the .NET 2.0 version of gacutil.exe, stored in C:\Program Files\Microsoft SDKs\Windows\v6.0A\bin

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Some more detail for completeness in case it helps someone...

Note that the most common reason for this exception these days is attempting to load a 32 bit-specific (/platform:x86) DLL into a process that is 64 bit or vice versa (viz. load a 64 bit-specific (/platform:x64) DLL into a process that is 32 bit). If your platform is non-specific (/platform:AnyCpu), this won't arise (assuming no referenced dependencies are of the wrong bitness).

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Obviously, as covered in the other answer, one will also need the .NET version number of the installutil you are running to be >= (preferably =) that of the EXE/DLL file you are running the installer of.

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Complete details of System.BadImageFormatException (saying the only cause is mismatched bittedness is really a gross oversimplification!).

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C# getting the path of %AppData%

To get the AppData directory, it's best to use the GetFolderPath method:

Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData)

(must add using System if not present).

%AppData% is an environment variable, and they are not automatically expanded anywhere in .NET, although you can explicitly use the Environment.ExpandEnvironmentVariable method to do so. I would still strongly suggest that you use GetFolderPath however, because as Johannes Rössel points out in the comment, %AppData% may not be set in certain circumstances.

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var fileName = Path.Combine(Environment.GetFolderPath(
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