31 Input/output library [input.output]

31.10 File-based streams [file.streams]

31.10.4 Class template basic_ifstream [ifstream]

31.10.4.2 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]).

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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).

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explicit basic_ifstream(const string& s,
                        ios_base::openmode mode = ios_base::in);

Effects: Equivalent to basic_ifstream(s.c_str(), mode).

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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).

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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.