29 Input/output library [input.output]

29.10 File-based streams [file.streams]

29.10.3 Class template basic_­ifstream [ifstream]

29.10.3.2 Constructors [ifstream.cons]

basic_ifstream();
Effects: Initializes the base class with basic_­istream<charT, traits>(addressof(sb)) ([istream.cons]) and sb with basic_­filebuf<charT, traits>() ([filebuf.cons]).
explicit basic_ifstream(const char* s, ios_base::openmode mode = ios_base::in); explicit basic_ifstream(const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in); // wide systems only; see [fstream.syn]
Effects: Initializes the base class with basic_­istream<charT, traits>(addressof(sb)) ([istream.cons]) and sb with basic_­filebuf<charT, traits>() ([filebuf.cons]), then calls rdbuf()->open(s, mode | ios_­base​::​in).
If that function returns a null pointer, calls setstate(failbit).
explicit basic_ifstream(const string& s, ios_base::openmode mode = ios_base::in);
Effects: Equivalent to: basic_­ifstream(s.c_­str(), mode).
template<class T> explicit basic_ifstream(const T& s, ios_base::openmode mode = ios_base::in);
Constraints: is_­same_­v<T, filesystem​::​path> is true.
Effects: Equivalent to: basic_­ifstream(s.c_­str(), mode).
basic_ifstream(basic_ifstream&& 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.