/FU (Name Forced #using File)
A compiler option that you can use as an alternative to passing a file name to #using Directive (C++) in source code.
The /FU switch takes just one file name. To specify multiple files, use /FU with each one.
If you are using C++/CLI and are referencing metadata to use the Friend Assemblies feature, you can't use /FU. You must reference the metadata in code by using #using—together with the [as friend] attribute. Friend assemblies are not supported in Visual C++ component extensions (C++/CX).
For information about how to create an assembly or module for the common language runtime (CLR), see /clr (Common Language Runtime Compilation). For information about how to build in C++/CX, see Building apps and libraries (C++/CX).
To set this compiler option in the Visual Studio development environment
Open the project's Property Pages dialog box. For details, see How to: Open Project Property Pages.
Select the C/C++ folder.
Select the Advanced property page.
Modify the Force #using property.
To set this compiler option programmatically