When IntelliSense Is Unavailable
There are certain cases when the IntelliSense options may not work as you expect.
By default, IntelliSense works automatically, but you can disable it.
Even when automatic statement completion is disabled, you can invoke an IntelliSense feature.
For more information, see Modifying IntelliSense Options.
Intellisense is not supported for projects that use the /clr compiler option.
For more information, see /clr (Common Language Runtime Compilation).
Make sure that your include directories and include files are set up correctly. Use the /I (Additional Include Directories) and the /INCLUDE (Force Symbol References) options to configure these settings.
For more information about the include directive, see #include Directive (C/C++) and Using C++ Library Headers.