30 Input/output library [input.output]

30.8 String-based streams [string.streams]

30.8.4 Class template basic_­ostringstream [ostringstream]

namespace std {
  template <class charT, class traits = char_traits<charT>,
            class Allocator = allocator<charT>>
  class basic_ostringstream : 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;
    using allocator_type = Allocator;

    // [ostringstream.cons], constructors
    explicit basic_ostringstream(
      ios_base::openmode which = ios_base::out);
    explicit basic_ostringstream(
      const basic_string<charT, traits, Allocator>& str,
      ios_base::openmode which = ios_base::out);
    basic_ostringstream(const basic_ostringstream& rhs) = delete;
    basic_ostringstream(basic_ostringstream&& rhs);

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

    // [ostringstream.members], members
    basic_stringbuf<charT, traits, Allocator>* rdbuf() const;

    basic_string<charT, traits, Allocator> str() const;
    void str(const basic_string<charT, traits, Allocator>& s);
   private:
    basic_stringbuf<charT, traits, Allocator> sb; // exposition only
  };

  template <class charT, class traits, class Allocator>
    void swap(basic_ostringstream<charT, traits, Allocator>& x,
              basic_ostringstream<charT, traits, Allocator>& y);
}
The class basic_­ostringstream<charT, traits, Allocator> supports writing objects of class basic_­string<​charT, traits, Allocator>.
It uses a basic_­stringbuf object to control the associated storage.
For the sake of exposition, the maintained data is presented here as:
  • sb, the stringbuf object.

30.8.4.1 basic_­ostringstream constructors [ostringstream.cons]

explicit basic_ostringstream( ios_base::openmode which = ios_base::out);
Effects: Constructs an object of class basic_­ostringstream<charT, traits>, initializing the base class with basic_­ostream<charT, traits>(&sb) ([ostream]) and initializing sb with basic_­stringbuf<charT, traits, Allocator>(which | ios_­base​::​out)) ([stringbuf.cons]).
explicit basic_ostringstream( const basic_string<charT, traits, Allocator>& str, ios_base::openmode which = ios_base::out);
Effects: Constructs an object of class basic_­ostringstream<charT, traits>, initializing the base class with basic_­ostream<charT, traits>(&sb) ([ostream]) and initializing sb with basic_­stringbuf<charT, traits, Allocator>(str, which | ios_­base​::​out)) ([stringbuf.cons]).
basic_ostringstream(basic_ostringstream&& rhs);
Effects: Move constructs from the rvalue rhs.
This is accomplished by move constructing the base class, and the contained basic_­stringbuf.
Next basic_­ostream<charT, traits>​::​set_­rdbuf(&sb) is called to install the contained basic_­stringbuf.

30.8.4.2 Assign and swap [ostringstream.assign]

basic_ostringstream& operator=(basic_ostringstream&& rhs);
Effects: Move assigns the base and members of *this from the base and corresponding members of rhs.
Returns: *this.
void swap(basic_ostringstream& rhs);
Effects: Exchanges the state of *this and rhs by calling basic_­ostream<charT, traits>​::​swap(rhs) and sb.swap(rhs.sb).
template <class charT, class traits, class Allocator> void swap(basic_ostringstream<charT, traits, Allocator>& x, basic_ostringstream<charT, traits, Allocator>& y);
Effects: As if by x.swap(y).

30.8.4.3 Member functions [ostringstream.members]

basic_stringbuf<charT, traits, Allocator>* rdbuf() const;
Returns: const_­cast<basic_­stringbuf<charT, traits, Allocator>*>(&sb).
basic_string<charT, traits, Allocator> str() const;
Returns: rdbuf()->str().
void str(const basic_string<charT, traits, Allocator>& s);
Effects: Calls rdbuf()->str(s).