29 Input/output library [input.output]

29.9 File-based streams [file.streams]

29.9.5 Class template basic_­fstream [fstream]

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);
    explicit basic_fstream(
      const filesystem::path& s,
      ios_base::openmode mode = ios_base::in | ios_base::out);
    basic_fstream(const basic_fstream&) = delete;
    basic_fstream(basic_fstream&& rhs);

    // [fstream.assign], assign and swap
    basic_fstream& operator=(const basic_fstream&) = delete;
    basic_fstream& operator=(basic_fstream&& rhs);
    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
  };

  template<class charT, class traits>
    void swap(basic_fstream<charT, traits>& x,
              basic_fstream<charT, traits>& y);
}
1
#
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.

29.9.5.1 Constructors [fstream.cons]

🔗
basic_fstream();
1
#
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]
2
#
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); explicit basic_fstream( const filesystem::path& s, ios_base::openmode mode = ios_base::in | ios_base::out);
3
#
Effects: Equivalent to: basic_­fstream(s.c_­str(), mode).
🔗
basic_fstream(basic_fstream&& rhs);
4
#
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.

29.9.5.2 Assignment and swap [fstream.assign]

🔗
void swap(basic_fstream& rhs);
1
#
Effects: Exchanges the state of *this and rhs by calling basic_­iostream<charT,traits>​::​swap(rhs) and sb.swap(rhs.sb).
🔗
template<class charT, class traits> void swap(basic_fstream<charT, traits>& x, basic_fstream<charT, traits>& y);
2
#
Effects: Equivalent to: x.swap(y).

29.9.5.3 Member functions [fstream.members]

🔗
basic_filebuf<charT, traits>* rdbuf() const;
1
#
Returns: const_­cast<basic_­filebuf<charT, traits>*>(addressof(sb)).
🔗
bool is_open() const;
2
#
Returns: rdbuf()->is_­open().
🔗
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]
3
#
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]).
🔗
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);
4
#
Effects: Calls open(s.c_­str(), mode).
🔗
void close();
5
#
Effects: Calls rdbuf()->close() and, if that function returns a null pointer, calls setstate(failbit) (which may throw ios_­base​::​failure) ([iostate.flags]).