27 Input/output library [input.output]

27.8 String-based streams [string.streams]

27.8.4 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);
}
1

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:

  • (1.1)

    sb, the stringbuf object.

27.8.4.1 basic_ostringstream constructors [ostringstream.cons]

explicit basic_ostringstream( ios_base::openmode which = ios_base::out);

1

Effects: Constructs an object of class basic_ostringstream, initializing the base class with basic_ostream(&sb) 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);

2

Effects: Constructs an object of class basic_ostringstream<charT, traits>, initializing the base class with basic_ostream(&sb) and initializing sb with basic_stringbuf<charT, traits, Allocator>(str, which | ios_base::out)) ([stringbuf.cons]).

basic_ostringstream(basic_ostringstream&& rhs);

3

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.

27.8.4.2 Assign and swap [ostringstream.assign]

basic_ostringstream& operator=(basic_ostringstream&& rhs);

1

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

2

Returns: *this.

void swap(basic_ostringstream& rhs);

3

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);

4

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

27.8.4.3 Member functions [ostringstream.members]

basic_stringbuf<charT, traits, Allocator>* rdbuf() const;

1

Returns: const_cast<basic_stringbuf<charT, traits, Allocator>*>(&sb).

basic_string<charT, traits, Allocator> str() const;

2

Returns: rdbuf()->str().

void str(const basic_string<charT, traits, Allocator>& s);

3

Effects: Calls rdbuf()->str(s).