30 Input/output library [input.output]

30.9 File-based streams [file.streams]

30.9.4 Class template basic_ofstream [ofstream]

namespace std {
  template <class charT, class traits = char_traits<charT>>
  class basic_ofstream : public basic_ostream<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;

    // [ofstream.cons], constructors
    basic_ofstream();
    explicit basic_ofstream(const char* s,
                            ios_base::openmode mode = ios_base::out);
    explicit basic_ofstream(const filesystem::path::value_type* s,
                            ios_base::openmode mode = ios_base::out);  // wide systems only; see [fstream.syn]
    explicit basic_ofstream(const string& s,
                            ios_base::openmode mode = ios_base::out);
    explicit basic_ofstream(const filesystem::path& s,
                            ios_base::openmode mode = ios_base::out);
    basic_ofstream(const basic_ofstream& rhs) = delete;
    basic_ofstream(basic_ofstream&& rhs);

    // [ofstream.assign], assign and swap
    basic_ofstream& operator=(const basic_ofstream& rhs) = delete;
    basic_ofstream& operator=(basic_ofstream&& rhs);
    void swap(basic_ofstream& rhs);

    // [ofstream.members], members
    basic_filebuf<charT, traits>* rdbuf() const;

    bool is_open() const;
    void open(const char* s, ios_base::openmode mode = ios_base::out);
    void open(const filesystem::path::value_type* s,
              ios_base::openmode mode = ios_base::out);  // wide systems only; see [fstream.syn]
    void open(const string& s, ios_base::openmode mode = ios_base::out);
    void open(const filesystem::path& s, ios_base::openmode mode = ios_base::out);
    void close();
  private:
    basic_filebuf<charT, traits> sb; // exposition only
  };

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

The class basic_ofstream<charT, traits> supports writing to named files.

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

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

(1.1)
sb, the filebuf object.

30.9.4.1 basic_ofstream constructors [ofstream.cons]

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basic_ofstream();

Effects: Constructs an object of class basic_ofstream<charT, traits>, initializing the base class with basic_ostream(&sb) and initializing sb with basic_filebuf<charT, traits>()) ([ostream.cons], [filebuf.cons]).

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

If that function returns a null pointer, calls setstate(failbit).

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explicit basic_ofstream(const string& s,
                        ios_base::openmode mode = ios_base::out);
explicit basic_ofstream(const filesystem::path& s,
                        ios_base::openmode mode = ios_base::out);

Effects: The same as basic_ofstream(s.c_str(), mode).

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basic_ofstream(basic_ofstream&& rhs);

Effects: Move constructs from the rvalue rhs.

This is accomplished by move constructing the base class, and the contained basic_filebuf.

Next basic_ostream<charT, traits>::set_rdbuf(&sb) is called to install the contained basic_filebuf.

30.9.4.2 Assign and swap [ofstream.assign]

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basic_ofstream& operator=(basic_ofstream&& rhs);

Effects: Move assigns the base and members of *this from the base and corresponding members of rhs.

Returns: *this.

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void swap(basic_ofstream& rhs);

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

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

Effects: As if by x.swap(y).

30.9.4.3 Member functions [ofstream.members]

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

Returns: const_cast<basic_filebuf<charT, traits>*>(&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::out);
void open(const filesystem::path::value_type* s,
          ios_base::openmode mode = ios_base::out);  // wide systems only; see [fstream.syn]

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

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 close();

Effects: Calls rdbuf()->close() and, if that function fails (returns a null pointer), 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::out);
void open(const filesystem::path& s, ios_base::openmode mode = ios_base::out);

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