31 Input/output library [input.output]

31.10 File-based streams [file.streams]

31.10.5 Class template basic_fstream [fstream]

31.10.5.1 General [fstream.general]

namespace std { template<class charT, class traits = char_traits<charT>> class basic_fstream : public basic_iostream<charT, traits> { public: using char_type = charT; using int_type = typename traits::int_type; using pos_type = typename traits::pos_type; using off_type = typename traits::off_type; using traits_type = traits; // [fstream.cons], constructors basic_fstream(); 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] explicit basic_fstream( const string& s, ios_base::openmode mode = ios_base::in | ios_base::out); template<class T> explicit basic_fstream(const T& s, ios_base::openmode mode = ios_base::in | ios_base::out); basic_fstream(const basic_fstream&) = delete; basic_fstream(basic_fstream&& rhs); basic_fstream& operator=(const basic_fstream&) = delete; basic_fstream& operator=(basic_fstream&& rhs); // [fstream.swap], swap void swap(basic_fstream& rhs); // [fstream.members], members basic_filebuf<charT, traits>* rdbuf() const; bool is_open() const; void open( const char* s, ios_base::openmode mode = ios_base::in | ios_base::out); void open( const filesystem::path::value_type* s, ios_base::openmode mode = ios_base::in|ios_base::out); // wide systems only; see [fstream.syn] void open( const string& s, ios_base::openmode mode = ios_base::in | ios_base::out); void open( const filesystem::path& s, ios_base::openmode mode = ios_base::in | ios_base::out); void close(); private: basic_filebuf<charT, traits> sb; // exposition only }; }

The class template basic_fstream<charT, traits> supports reading and writing from named files.

It uses a basic_filebuf<charT, traits> object to control the associated sequences.

For the sake of exposition, the maintained data is presented here as:

(1.1)
sb, the basic_filebuf object.

31.10.5.2 Constructors [fstream.cons]

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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.

31.10.5.3 Swap [fstream.swap]

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void swap(basic_fstream& rhs);

Effects: Exchanges the state of *this and rhs by calling basic_iostream<charT,traits>::swap(rhs) and sb.swap(rhs.sb).

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template<class charT, class traits>
  void swap(basic_fstream<charT, traits>& x,
            basic_fstream<charT, traits>& y);

Effects: Equivalent to: x.swap(y).

31.10.5.4 Member functions [fstream.members]

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basic_filebuf<charT, traits>* rdbuf() const;

Returns: const_cast<basic_filebuf<charT, traits>*>(addressof(sb)).

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bool is_open() const;

Returns: rdbuf()->is_open().

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void open(
  const char* s,
  ios_base::openmode mode = ios_base::in | ios_base::out);
void open(
  const filesystem::path::value_type* s,
  ios_base::openmode mode = ios_base::in | ios_base::out);  // wide systems only; see [fstream.syn]

Effects: Calls rdbuf()->open(s, mode).

If that function does not return a null pointer calls clear(), otherwise calls setstate(failbit) (which may throw ios_base::failure) ([iostate.flags]).

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void open(
  const string& s,
  ios_base::openmode mode = ios_base::in | ios_base::out);
void open(
  const filesystem::path& s,
  ios_base::openmode mode = ios_base::in | ios_base::out);

Effects: Calls open(s.c_str(), mode).

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void close();

Effects: Calls rdbuf()->close() and, if that function returns a null pointer, calls setstate(failbit) (which may throw ios_base::failure) ([iostate.flags]).