31 Input/output library [input.output]

31.10 File-based streams [file.streams]

31.10.5 Class template basic_fstream [fstream]

31.10.5.2 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>().

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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).

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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).

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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).

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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.