30 Input/output library [input.output]

30.10 File systems [filesystems]

30.10.4 Terms and definitions [fs.definitions]

30.10.4.9 native encoding [fs.def.native.encode]

For narrow character strings, the operating system dependent current encoding for pathnames ([fs.def.pathname]).
For wide character strings, the implementation-defined execution wide-character set encoding ([lex.charset]).