I am using Visual Studio 2015 Community Edition.
In VS2015 installer, selecting Common Tools and MFC Components under the Visual C++ node, I am able to build ATL based projects.
Selecting Tools and Windows SDKs, under Windows 8.1 and Windows Phone Tools node, I am able to build MFC projects based on Platform Toolset v120, that is Visual Studio 2013.
Now I would like to build an existing ATL project, relatively large, originally built in Visual Studio 2013.
When I set Platform Toolset = 'v120' in the ATL project, the compiler is unable to find the ATL headers.
Is it possible to install them? Do I have to install both VS2013 and VS2015?
You do need to install the earlier version of Visual Studio if you want to use its compiler toolchain. You can also open a developer command prompt to select the compiler version and use msbuild to build the target using that specific compiler but you still need to have installed the compiler version you need.