30 Input/output library [input.output]

30.9 File-based streams [file.streams]

30.9.5 Class template basic_­fstream [fstream]

30.9.5.1 basic_­fstream constructors [fstream.cons]

basic_fstream();
Effects: Constructs an object of class basic_­fstream<charT, traits>, initializing the base class with basic_­iostream<charT, traits>(&sb) ([iostream.cons]) and initializing sb with basic_­filebuf<charT, traits>().
explicit basic_fstream( const char* s, ios_base::openmode mode = ios_base::in | ios_base::out); explicit basic_fstream( const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in | ios_base::out); // wide systems only; see [fstream.syn]
Effects: Constructs an object of class basic_­fstream<charT, traits>, initializing the base class with basic_­iostream<charT, traits>(&sb) ([iostream.cons]) and initializing sb with basic_­filebuf<charT, traits>().
Then calls rdbuf()->open(s, mode).
If that function returns a null pointer, calls setstate(failbit).
explicit basic_fstream( const string& s, ios_base::openmode mode = ios_base::in | ios_base::out); explicit basic_fstream( const filesystem::path& s, ios_base::openmode mode = ios_base::in | ios_base::out);
Effects: The same as basic_­fstream(s.c_­str(), mode).
basic_fstream(basic_fstream&& rhs);
Effects: Move constructs from the rvalue rhs.
This is accomplished by move constructing the base class, and the contained basic_­filebuf.
Next basic_­istream<charT, traits>​::​set_­rdbuf(&sb) is called to install the contained basic_­filebuf.