29 Input/output library [input.output]

29.10 File-based streams [file.streams]

29.10.5 Class template basic_­fstream [fstream]

29.10.5.2 Constructors [fstream.cons]

basic_fstream();
Effects: Initializes the base class with basic_­iostream<charT, traits>(addressof(sb)) ([iostream.cons]) and 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: Initializes the base class with basic_­iostream<charT, traits>(addressof(sb)) ([iostream.cons]) and 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);
Effects: Equivalent to: basic_­fstream(s.c_­str(), mode).
template<class T> explicit basic_fstream(const T& s, ios_base::openmode mode = ios_base::in | ios_base::out);
Constraints: is_­same_­v<T, filesystem​::​path> is true.
Effects: Equivalent to: basic_­fstream(s.c_­str(), mode).
basic_fstream(basic_fstream&& rhs);
Effects: Move constructs the base class, and the contained basic_­filebuf.
Then calls basic_­istream<charT, traits>​::​set_­rdbuf(​addressof(sb)) to install the contained basic_­filebuf.