This compiler directive is obsolete starting in Visual Studio 2015 Update 2.
We recommend that you use the /execution-charset:utf-8 or /utf-8
compiler options together with using the u8 prefix on narrow character and string literals
that contain extended characters. For more information about the u8 prefix,
see String and Character Literals. For more information about the compiler options,
see /execution-charset (Set Execution Character Set) and /utf-8 (Set Source and Executable character sets to UTF-8).
https://docs.microsoft.com/en-us/cpp/preprocessor/execution-character-set?view=msvc-160
https://docs.microsoft.com/en-us/cpp/build/reference/execution-charset-set-execution-character-set?view=msvc-160