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1 | 1 | --- |
2 | 2 | description: "Learn more about: Redistributing Components By Using Merge Modules" |
3 | 3 | title: "Redistributing Components By Using Merge Modules" |
4 | | -ms.date: 02/15/2022 |
| 4 | +ms.date: 06/08/2022 |
5 | 5 | helpviewer_keywords: ["merge modules, using", "redistributing applications, using merge modules"] |
6 | 6 | ms.assetid: 93b84211-bf9b-4a78-9f22-474ac2ef7840 |
7 | 7 | --- |
8 | 8 | # Redistributing components by using merge modules |
9 | 9 |
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10 | 10 | > [!IMPORTANT] |
11 | | -> In Visual Studio 2019 and later, merge modules for Visual C++ Redistributable files are deprecated. We don't recommend you use them for application deployment. Merge modules make it difficult to service Visual C++ Runtime files independently of your application. Instead, we recommend you use central deployment of the Visual C++ Redistributable package. Central deployment installs the Redistributable files in the Windows *`%SYSTEMROOT%\system32\`* folder for use by all applications and users. Central deployment by a Redistributable package makes it possible for Microsoft to service runtime library files independently. And, an uninstall of your app can't break other applications that also use central deployment. When you use a Redistributable package for central deployment, you aren't responsible for tracking and updating the runtime libraries as part of your application maintenance: The Microsoft Update service updates these libraries for you. Otherwise, an update to the runtime library files requires you to update and redeploy your *`.msi`* installer. Your app could be vulnerable to bugs or security issues until you do. |
| 11 | +> In Visual Studio 2019 and later, merge modules for Visual C++ Redistributable files are deprecated. We don't recommend you use them for application deployment. Redistributables installed using Merge modules can't be updated by Windows Update because the detection mechanism depends on knowing details of the installing package. The Visual C++ Redistributable packages are known for each release, but packages that use MSMs are user generated. Microsoft can't know the details of user-generated packages. Instead, we recommend you use central deployment of the Visual C++ Redistributable package. Central deployment installs the Redistributable files in the Windows *`%SYSTEMROOT%\system32\`* folder for use by all applications and users. Central deployment by a Redistributable package makes it possible for Microsoft to service runtime library files independently. And, an uninstall of your app can't break other applications that also use central deployment. When you use a Redistributable package for central deployment, you aren't responsible for tracking and updating the runtime libraries as part of your application maintenance: The Microsoft Update service updates these libraries for you. Otherwise, an update to the runtime library files requires you to update and redeploy your *`.msi`* installer. Your app could be vulnerable to bugs or security issues until you do. |
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13 | 13 | Visual Studio includes [merge modules](/windows/win32/Msi/about-merge-modules) (*`.msm`* files) for each Visual C++ component that's licensed for redistribution with an application. There are separate versions of the merge modules for each target platform. When a merge module is compiled into a Windows Installer setup file, it enables the deployment of Visual C++ Redistributable files to that specific platform. You can't include merge modules for different versions of the same DLL in one installer. In your installer setup file, specify that the merge modules are prerequisites for your application. |
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15 | 15 | You can use merge modules for either [central deployment](deployment-in-visual-cpp.md#central-deployment) or [local deployment](deployment-in-visual-cpp.md#local-deployment). Users can't install centrally deployed files unless they have administrator rights. Local deployment may allow a non-administrator to install and run your app, but at the cost of independent serviceability. |
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17 | 17 | The installation service reports an error if you attempt central deployment of older merge modules over newer existing libraries. You should write your installer setup to handle this failure gracefully and not display an error message. Your code can still deploy and run successfully despite this failure. For more information, see [C++ binary compatibility between Visual Studio versions](../porting/binary-compat-2015-2017.md). |
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19 | | -If you deploy your code only as an *`.msi`* installer, we recommend you don't include the merge modules in the installer. Instead, report a failure to the user when the required Redistributable libraries aren't found. In the failure dialog, include instructions on how to find and install the latest Redistributable package. |
| 19 | +If you deploy your code only as an *`.msi`* installer, we recommend you don't include the merge modules in the installer. Instead, report a failure to the user when the required Redistributable libraries aren't found. In the failure dialog, include instructions on how to find and install the latest Redistributable package. For more information and links to Redistributable packages, see [The latest supported Visual C++ downloads](latest-supported-vc-redist.md). |
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21 | | -The latest Redistributable packages and merge modules are compatible with code built using Visual Studio 2015 and later. Code built by versions of Visual Studio before 2015 require a separate Redistributable package. For more information and links to Redistributable packages, see [The latest supported Visual C++ downloads](latest-supported-vc-redist.md). |
| 21 | +The latest Redistributable packages and merge modules are compatible with code built using Visual Studio 2015 and later. Code built by versions of Visual Studio before 2015 require a separate Redistributable package. |
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23 | 23 | ## When to use merge modules |
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25 | 25 | Merge modules are only appropriate in limited circumstances: |
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27 | 27 | - You can't install or require a separate Redistributable package for policy reasons, |
| 28 | +- Your code requires a specific, bug-compatible version of the libraries, |
28 | 29 | - Your code only targets one platform, and you don't have dependencies on more than one version of the DLLs, |
29 | 30 | - You intend to service your deployed code regularly, so the libraries remain up to date. |
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