29 Input/output library [input.output]

29.8 String-based streams [string.streams]

29.8.1 Header <sstream> synopsis [sstream.syn]

namespace std {
  template<class charT, class traits = char_traits<charT>,
           class Allocator = allocator<charT>>
    class basic_stringbuf;

  using stringbuf  = basic_stringbuf<char>;
  using wstringbuf = basic_stringbuf<wchar_t>;

  template<class charT, class traits = char_traits<charT>,
           class Allocator = allocator<charT>>
    class basic_istringstream;

  using istringstream  = basic_istringstream<char>;
  using wistringstream = basic_istringstream<wchar_t>;

  template<class charT, class traits = char_traits<charT>,
           class Allocator = allocator<charT>>
    class basic_ostringstream;
  using ostringstream  = basic_ostringstream<char>;
  using wostringstream = basic_ostringstream<wchar_t>;

  template<class charT, class traits = char_traits<charT>,
           class Allocator = allocator<charT>>
    class basic_stringstream;
  using stringstream  = basic_stringstream<char>;
  using wstringstream = basic_stringstream<wchar_t>;
}

The header <sstream> defines four class templates and eight types that associate stream buffers with objects of class basic_string, as described in [string.classes].

29.8.2 Class template basic_stringbuf [stringbuf]

namespace std {
  template<class charT, class traits = char_traits<charT>,
           class Allocator = allocator<charT>>
  class basic_stringbuf : public basic_streambuf<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;

    // [stringbuf.cons], constructors
    basic_stringbuf() : basic_stringbuf(ios_base::in | ios_base::out) {}
    explicit basic_stringbuf(ios_base::openmode which);
    explicit basic_stringbuf(
      const basic_string<charT, traits, Allocator>& s,
      ios_base::openmode which = ios_base::in | ios_base::out);
    explicit basic_stringbuf(const Allocator& a)
      : basic_stringbuf(ios_base::in | ios_base::out, a) {}
    basic_stringbuf(ios_base::openmode which, const Allocator& a);
    explicit basic_stringbuf(
      basic_string<charT, traits, Allocator>&& s,
      ios_base::openmode which = ios_base::in | ios_base::out);
    template<class SAlloc>
      basic_stringbuf(
        const basic_string<charT, traits, SAlloc>& s, const Allocator& a)
        : basic_stringbuf(s, ios_base::in | ios_base::out, a) {}
    template<class SAlloc>
      basic_stringbuf(
        const basic_string<charT, traits, SAlloc>& s,
        ios_base::openmode which, const Allocator& a);
    template<class SAlloc>
      explicit basic_stringbuf(
        const basic_string<charT, traits, SAlloc>& s,
        ios_base::openmode which = ios_base::in | ios_base::out);
    basic_stringbuf(const basic_stringbuf&) = delete;
    basic_stringbuf(basic_stringbuf&& rhs);
    basic_stringbuf(basic_stringbuf&& rhs, const Allocator& a);

    // [stringbuf.assign], assign and swap
    basic_stringbuf& operator=(const basic_stringbuf&) = delete;
    basic_stringbuf& operator=(basic_stringbuf&& rhs);
    void swap(basic_stringbuf& rhs) noexcept(see below);

    // [stringbuf.members], getters and setters
    allocator_type get_allocator() const noexcept;

    basic_string<charT, traits, Allocator> str() const &;
    template<class SAlloc>
      basic_string<charT,traits,SAlloc> str(const SAlloc& sa) const;
    basic_string<charT, traits, Allocator> str() &&;
    basic_string_view<charT, traits> view() const noexcept;

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

  protected:
    // [stringbuf.virtuals], overridden virtual functions
    int_type underflow() override;
    int_type pbackfail(int_type c = traits::eof()) override;
    int_type overflow (int_type c = traits::eof()) override;
    basic_streambuf<charT, traits>* setbuf(charT*, streamsize) override;

    pos_type seekoff(off_type off, ios_base::seekdir way,
                     ios_base::openmode which
                      = ios_base::in | ios_base::out) override;
    pos_type seekpos(pos_type sp,
                     ios_base::openmode which
                      = ios_base::in | ios_base::out) override;

  private:
    ios_base::openmode mode;                        // exposition only
    basic_string<charT, traits, Allocator> buf;     // exposition only
    void init_buf_ptrs();                           // exposition only
  };

  template<class charT, class traits, class Allocator>
    void swap(basic_stringbuf<charT, traits, Allocator>& x,
              basic_stringbuf<charT, traits, Allocator>& y) noexcept(noexcept(x.swap(y)));
}

The class basic_stringbuf is derived from basic_streambuf to associate possibly the input sequence and possibly the output sequence with a sequence of arbitrary characters.

The sequence can be initialized from, or made available as, an object of class basic_string.

For the sake of exposition, the maintained data and internal pointer initialization is presented here as:

(2.1)
ios_base::openmode mode, has in set if the input sequence can be read, and out set if the output sequence can be written.
(2.2)
basic_string<charT, traits, Allocator> buf contains the underlying character sequence.
(2.3)
init_buf_ptrs() sets the base class' get area ([streambuf.get.area]) and put area ([streambuf.put.area]) pointers after initializing, moving from, or assigning to buf accordingly.

29.8.2.1 Constructors [stringbuf.cons]

🔗

explicit basic_stringbuf(ios_base::openmode which);

Effects: Initializes the base class with basic_streambuf() ([streambuf.cons]), and mode with which.

It is implementation-defined whether the sequence pointers (eback(), gptr(), egptr(), pbase(), pptr(), epptr()) are initialized to null pointers.

Postconditions: str().empty() is true.

🔗

explicit basic_stringbuf(
  const basic_string<charT, traits, Allocator>& s,
  ios_base::openmode which = ios_base::in | ios_base::out);

Effects: Initializes the base class with basic_streambuf() ([streambuf.cons]), mode with which, and buf with s, then calls init_buf_ptrs().

🔗

basic_stringbuf(ios_base::openmode which, const Allocator &a);

Effects: Initializes the base class with basic_streambuf() ([streambuf.cons]), mode with which, and buf with a, then calls init_buf_ptrs().

Postconditions: str().empty() is true.

🔗

explicit basic_stringbuf(
  basic_string<charT, traits, Allocator>&& s,
  ios_base::openmode which = ios_base::in | ios_base::out);

Effects: Initializes the base class with basic_streambuf() ([streambuf.cons]), mode with which, and buf with std::move(s), then calls init_buf_ptrs().

🔗

template<class SAlloc>
  basic_stringbuf(
    const basic_string<charT, traits, SAlloc>& s,
    ios_base::openmode which, const Allocator &a);

Effects: Initializes the base class with basic_streambuf() ([streambuf.cons]), mode with which, and buf with {s,a}, then calls init_buf_ptrs().

🔗

template<class SAlloc>
  explicit basic_stringbuf(
    const basic_string<charT, traits, SAlloc>& s,
    ios_base::openmode which = ios_base::in | ios_base::out);

Constraints: is_same_v<SAlloc,Allocator> is false.

Effects: Initializes the base class with basic_streambuf() ([streambuf.cons]), mode with which, and buf with s, then calls init_buf_ptrs().

🔗

basic_stringbuf(basic_stringbuf&& rhs);
basic_stringbuf(basic_stringbuf&& rhs, const Allocator& a);

Effects: Copy constructs the base class from rhs and initializes mode with rhs.mode.

In the first form buf is initialized from std::move(rhs).str().

In the second form buf is initialized from {std::move(rhs).str(), a}.

It is implementation-defined whether the sequence pointers in *this (eback(), gptr(), egptr(), pbase(), pptr(), epptr()) obtain the values which rhs had.

Postconditions: Let rhs_p refer to the state of rhs just prior to this construction and let rhs_a refer to the state of rhs just after this construction.

(11.1)
str() == rhs_p.str()
(11.2)
gptr() - eback() == rhs_p.gptr() - rhs_p.eback()
(11.3)
egptr() - eback() == rhs_p.egptr() - rhs_p.eback()
(11.4)
pptr() - pbase() == rhs_p.pptr() - rhs_p.pbase()
(11.5)
epptr() - pbase() == rhs_p.epptr() - rhs_p.pbase()
(11.6)
if (eback()) eback() != rhs_a.eback()
(11.7)
if (gptr()) gptr() != rhs_a.gptr()
(11.8)
if (egptr()) egptr() != rhs_a.egptr()
(11.9)
if (pbase()) pbase() != rhs_a.pbase()
(11.10)
if (pptr()) pptr() != rhs_a.pptr()
(11.11)
if (epptr()) epptr() != rhs_a.epptr()
(11.12)
getloc() == rhs_p.getloc()
(11.13)
rhs is empty but usable, as if std::move(rhs).str() was called.

29.8.2.2 Assignment and swap [stringbuf.assign]

🔗

basic_stringbuf& operator=(basic_stringbuf&& rhs);

Effects: After the move assignment *this has the observable state it would have had if it had been move constructed from rhs (see [stringbuf.cons]).

Returns: *this.

🔗

void swap(basic_stringbuf& rhs) noexcept(see below);

Preconditions: allocator_traits<Allocator>::propagate_on_container_swap::value is true or get_allocator() == s.get_allocator() is true.

Effects: Exchanges the state of *this and rhs.

Remarks: The expression inside noexcept is equivalent to:

allocator_traits<Allocator>::propagate_on_container_swap::value ||

allocator_traits<Allocator>::is_always_equal::value.

🔗

template<class charT, class traits, class Allocator>
  void swap(basic_stringbuf<charT, traits, Allocator>& x,
            basic_stringbuf<charT, traits, Allocator>& y) noexcept(noexcept(x.swap(y)));

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

29.8.2.3 Member functions [stringbuf.members]

The member functions getting the underlying character sequence all refer to a high_mark value, where high_mark represents the position one past the highest initialized character in the buffer.

Characters can be initialized by writing to the stream, by constructing the basic_stringbuf passing a basic_string argument, or by calling one of the str member functions passing a basic_string as an argument.

In the latter case, all characters initialized prior to the call are now considered uninitialized (except for those characters re-initialized by the new basic_string).

🔗

void init_buf_ptrs(); // exposition only

Effects: Initializes the input and output sequences from buf according to mode.

Postconditions:

(3.1)
If ios_base::out is set in mode, pbase() points to buf.front() and epptr() >= pbase() + buf.size() is true;
- (3.1.1)
  in addition, if ios_base::ate is set in mode, pptr() == pbase() + buf.size() is true,
- (3.1.2)
  otherwise pptr() == pbase() is true.
(3.2)
If ios_base::in is set in mode, eback() points to buf.front(), and (gptr() == eback() && egptr() == eback() + buf.size()) is true.

[ Note

For efficiency reasons, stream buffer operations might violate invariants of buf while it is held encapsulated in the basic_stringbuf, e.g., by writing to characters in the range [buf.data() + buf.size(), buf.data() + buf.capacity()).

All operations retrieving a basic_string from buf ensure that the basic_string invariants hold on the returned value.

— end note

]

🔗

allocator_type get_allocator() const noexcept;

Returns: buf.get_allocator().

🔗

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

Effects: Equivalent to:

return basic_string<charT, traits, Allocator>(view(), get_allocator());

🔗

template<class SAlloc>
  basic_string<charT, traits, SAlloc> str(const SAlloc& sa) const;

Constraints: SAlloc is a type that qualifies as an allocator ([container.requirements.general]).

Effects: Equivalent to:

return basic_string<charT, traits, SAlloc>(view(), sa);

🔗

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

Returns: A basic_string<charT, traits, Allocator> object move constructed from the basic_stringbuf's underlying character sequence in buf.

This can be achieved by first adjusting buf to have the same content as view().

Postconditions: The underlying character sequence buf is empty and pbase(), pptr(), epptr(), eback(), gptr(), and egptr() are initialized as if by calling init_buf_ptrs() with an empty buf.

🔗

basic_string_view<charT, traits> view() const noexcept;

Let sv be basic_string_view<charT, traits>.

Returns: A sv object referring to the basic_stringbuf's underlying character sequence in buf:

(12.1)
If ios_base::out is set in mode, then sv(pbase(), high_mark-pbase()) is returned.
(12.2)
Otherwise, if ios_base::in is set in mode, then sv(eback(), egptr()-eback()) is returned.
(12.3)
Otherwise, sv() is returned.

[ Note

Using the returned sv object after destruction or invalidation of the character sequence underlying *this is undefined behavior, unless sv.empty() is true.

— end note

]

🔗

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

Effects: Equivalent to:

buf = s;
init_buf_ptrs();

🔗

template<class SAlloc>
  void str(const basic_string<charT, traits, SAlloc>& s);

Constraints: is_same_v<SAlloc,Allocator> is false.

Effects: Equivalent to:

buf = s;
init_buf_ptrs();

🔗

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

Effects: Equivalent to:

buf = std::move(s);
init_buf_ptrs();

29.8.2.4 Overridden virtual functions [stringbuf.virtuals]

🔗

int_type underflow() override;

Returns: If the input sequence has a read position available, returns traits::to_int_type(*gptr()).

Otherwise, returns traits::eof().

Any character in the underlying buffer which has been initialized is considered to be part of the input sequence.

🔗

int_type pbackfail(int_type c = traits::eof()) override;

Effects: Puts back the character designated by c to the input sequence, if possible, in one of three ways:

(2.1)
If traits::eq_int_type(c, traits::eof()) returns false and if the input sequence has a putback position available, and if traits::eq(to_char_type(c), gptr()[-1]) returns true, assigns gptr() - 1 to gptr().
Returns: c.
(2.2)
If traits::eq_int_type(c, traits::eof()) returns false and if the input sequence has a putback position available, and if mode & ios_base::out is nonzero, assigns c to *--gptr().
Returns: c.
(2.3)
If traits::eq_int_type(c, traits::eof()) returns true and if the input sequence has a putback position available, assigns gptr() - 1 to gptr().
Returns: traits::not_eof(c).

Returns: As specified above, or traits::eof() to indicate failure.

Remarks: If the function can succeed in more than one of these ways, it is unspecified which way is chosen.

🔗

int_type overflow(int_type c = traits::eof()) override;

Effects: Appends the character designated by c to the output sequence, if possible, in one of two ways:

(5.1)
If traits::eq_int_type(c, traits::eof()) returns false and if either the output sequence has a write position available or the function makes a write position available (as described below), the function calls sputc(c).
Signals success by returning c.
(5.2)
If traits::eq_int_type(c, traits::eof()) returns true, there is no character to append.
Signals success by returning a value other than traits::eof().

Remarks: The function can alter the number of write positions available as a result of any call.

Returns: As specified above, or traits::eof() to indicate failure.

The function can make a write position available only if ios_base::out is set in mode.

To make a write position available, the function reallocates (or initially allocates) an array object with a sufficient number of elements to hold the current array object (if any), plus at least one additional write position.

If ios_base::in is set in mode, the function alters the read end pointer egptr() to point just past the new write position.

🔗

pos_type seekoff(off_type off, ios_base::seekdir way,
                 ios_base::openmode which
                   = ios_base::in | ios_base::out) override;

Effects: Alters the stream position within one of the controlled sequences, if possible, as indicated in Table 124 .

Table 124: seekoff positioning [tab:stringbuf.seekoff.pos]

Conditions	Result
ios_base::in is set in which	positions the input sequence
ios_base::out is set in which	positions the output sequence
both ios_base::in and ios_base::out are set in which and either way == ios_base::beg or way == ios_base::end	positions both the input and the output sequences
Otherwise	the positioning operation fails.

For a sequence to be positioned, the function determines newoff as indicated in Table 125 .

If the sequence's next pointer (either gptr() or pptr()) is a null pointer and newoff is nonzero, the positioning operation fails.

Table 125: newoff values [tab:stringbuf.seekoff.newoff]

Condition	newoff Value
way == ios_base::beg	0
way == ios_base::cur	the next pointer minus the beginning pointer (xnext - xbeg).
way == ios_base::end	the high mark pointer minus the beginning pointer (high_mark - xbeg).

If (newoff + off) < 0, or if newoff + off refers to an uninitialized character ([stringbuf.members]), the positioning operation fails.

Otherwise, the function assigns xbeg + newoff + off to the next pointer xnext.

Returns: pos_type(newoff), constructed from the resultant offset newoff (of type off_type), that stores the resultant stream position, if possible.

If the positioning operation fails, or if the constructed object cannot represent the resultant stream position, the return value is pos_type(off_type(-1)).

🔗

pos_type seekpos(pos_type sp,
                 ios_base::openmode which
                   = ios_base::in | ios_base::out) override;

Effects: Equivalent to seekoff(off_type(sp), ios_base::beg, which).

Returns: sp to indicate success, or pos_type(off_type(-1)) to indicate failure.

🔗

basic_streambuf<charT, traits>* setbuf(charT* s, streamsize n);

Effects: implementation-defined, except that setbuf(0, 0) has no effect.

Returns: this.

29.8.3 Class template basic_istringstream [istringstream]

namespace std {
  template<class charT, class traits = char_traits<charT>,
           class Allocator = allocator<charT>>
  class basic_istringstream : public basic_istream<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;

    // [istringstream.cons], constructors
    basic_istringstream() : basic_istringstream(ios_base::in) {}
    explicit basic_istringstream(ios_base::openmode which);
    explicit basic_istringstream(
      const basic_string<charT, traits, Allocator>& s,
      ios_base::openmode which = ios_base::in);
    basic_istringstream(ios_base::openmode which, const Allocator& a);
    explicit basic_istringstream(
      basic_string<charT, traits, Allocator>&& s,
      ios_base::openmode which = ios_base::in);
    template<class SAlloc>
      basic_istringstream(
        const basic_string<charT, traits, SAlloc>& s, const Allocator& a)
        : basic_istringstream(s, ios_base::in, a) {}
    template<class SAlloc>
      basic_istringstream(
        const basic_string<charT, traits, SAlloc>& s,
        ios_base::openmode which, const Allocator& a);
    template<class SAlloc>
      explicit basic_istringstream(
        const basic_string<charT, traits, SAlloc>& s,
        ios_base::openmode which = ios_base::in);
    basic_istringstream(const basic_istringstream&) = delete;
    basic_istringstream(basic_istringstream&& rhs);

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

    // [istringstream.members], members
    basic_stringbuf<charT, traits, Allocator>* rdbuf() const;
    basic_string<charT, traits, Allocator> str() const &;
    template<class SAlloc>
      basic_string<charT,traits,SAlloc> str(const SAlloc& sa) const;
    basic_string<charT, traits, Allocator> str() &&;
    basic_string_view<charT, traits> view() const noexcept;

    void str(const basic_string<charT, traits, Allocator>& s);
    template<class SAlloc>
      void str(const basic_string<charT, traits, SAlloc>& s);
    void str(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_istringstream<charT, traits, Allocator>& x,
              basic_istringstream<charT, traits, Allocator>& y);
}

The class basic_istringstream<charT, traits, Allocator> supports reading objects of class basic_string<charT, traits, Allocator>.

It uses a basic_stringbuf<charT, traits, Allocator> object to control the associated storage.

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

(1.1)
sb, the stringbuf object.

29.8.3.1 Constructors [istringstream.cons]

🔗

explicit basic_istringstream(ios_base::openmode which);

Effects: Initializes the base class with basic_istream<charT, traits>(addressof(sb)) ([istream]) and sb with basic_stringbuf<charT, traits, Allocator>(which | ios_base::in) ([stringbuf.cons]).

🔗

explicit basic_istringstream(
  const basic_string<charT, traits, Allocator>& s,
  ios_base::openmode which = ios_base::in);

Effects: Initializes the base class with basic_istream<charT, traits>(addressof(sb)) ([istream]) and sb with basic_stringbuf<charT, traits, Allocator>(s, which | ios_base::in)
([stringbuf.cons]).

🔗

basic_istringstream(ios_base::openmode which, const Allocator& a);

Effects: Initializes the base class with basic_istream<charT, traits>(addressof(sb)) ([istream]) and sb with basic_stringbuf<charT, traits, Allocator>(which | ios_base::in, a) ([stringbuf.cons]).

🔗

explicit basic_istringstream(
  basic_string<charT, traits, Allocator>&& s,
  ios_base::openmode which = ios_base::in);

Effects: Initializes the base class with basic_istream<charT, traits>(addressof(sb)) ([istream]) and sb with basic_stringbuf<charT, traits, Allocator>(std::move(s), which | ios_base::in) ([stringbuf.cons]).

🔗

template<class SAlloc>
  basic_istringstream(
    const basic_string<charT, traits, SAlloc>& s,
    ios_base::openmode which, const Allocator& a);

Effects: Initializes the base class with basic_istream<charT, traits>(addressof(sb)) ([istream]) and sb with basic_stringbuf<charT, traits, Allocator>(s, which | ios_base::in, a)
([stringbuf.cons]).

🔗

template<class SAlloc>
  explicit basic_istringstream(
    const basic_string<charT, traits, SAlloc>& s,
    ios_base::openmode which = ios_base::in);

Effects: Initializes the base class with basic_istream<charT, traits>(addressof(sb)) ([istream]) and sb with basic_stringbuf<charT, traits, Allocator>(s, which | ios_base::in) ([stringbuf.cons]).

🔗

basic_istringstream(basic_istringstream&& rhs);

Effects: Move constructs from the rvalue rhs.

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

Then calls basic_istream<charT, traits>::set_rdbuf(addressof(sb)) to install the contained basic_stringbuf.

29.8.3.2 Assignment and swap [istringstream.assign]

🔗

void swap(basic_istringstream& rhs);

Effects: Equivalent to:

basic_istream<charT, traits>::swap(rhs);
sb.swap(rhs.sb);

🔗

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

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

29.8.3.3 Member functions [istringstream.members]

🔗

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

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

🔗

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

Effects: Equivalent to: return rdbuf()->str();

🔗

template<class SAlloc>
  basic_string<charT,traits,SAlloc> str(const SAlloc& sa) const;

Effects: Equivalent to: return rdbuf()->str(sa);

🔗

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

Effects: Equivalent to: return std::move(*rdbuf()).str();

🔗

basic_string_view<charT, traits> view() const noexcept;

Effects: Equivalent to: return rdbuf()->view();

🔗

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

Effects: Equivalent to: rdbuf()->str(s);

🔗

template<class SAlloc>
  void str(const basic_string<charT, traits, SAlloc>& s);

Effects: Equivalent to: rdbuf()->str(s);

🔗

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

Effects: Equivalent to: rdbuf()->str(std::move(s));

29.8.4 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
    basic_ostringstream() : basic_ostringstream(ios_base::out) {}
    explicit basic_ostringstream(ios_base::openmode which);
    explicit basic_ostringstream(
      const basic_string<charT, traits, Allocator>& s,
      ios_base::openmode which = ios_base::out);
    basic_ostringstream(ios_base::openmode which, const Allocator& a);
    explicit basic_ostringstream(
      basic_string<charT, traits, Allocator>&& s,
      ios_base::openmode which = ios_base::out);
    template<class SAlloc>
      basic_ostringstream(
        const basic_string<charT, traits, SAlloc>& s, const Allocator& a)
        : basic_ostringstream(s, ios_base::out, a) {}
    template<class SAlloc>
      basic_ostringstream(
        const basic_string<charT, traits, SAlloc>& s,
        ios_base::openmode which, const Allocator& a);
    template<class SAlloc>
      explicit basic_ostringstream(
        const basic_string<charT, traits, SAlloc>& s,
        ios_base::openmode which = ios_base::out);
    basic_ostringstream(const basic_ostringstream&) = delete;
    basic_ostringstream(basic_ostringstream&& rhs);

    // [ostringstream.assign], assign and swap
    basic_ostringstream& operator=(const basic_ostringstream&) = 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 &;
    template<class SAlloc>
      basic_string<charT,traits,SAlloc> str(const SAlloc& sa) const;
    basic_string<charT, traits, Allocator> str() &&;
    basic_string_view<charT, traits> view() const noexcept;

    void str(const basic_string<charT, traits, Allocator>& s);
    template<class SAlloc>
      void str(const basic_string<charT, traits, SAlloc>& s);
    void str(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:

(1.1)
sb, the stringbuf object.

29.8.4.1 Constructors [ostringstream.cons]

🔗

explicit basic_ostringstream(ios_base::openmode which);

Effects: Initializes the base class with basic_ostream<charT, traits>(addressof(sb)) ([ostream]) and sb with basic_stringbuf<charT, traits, Allocator>(which | ios_base::out) ([stringbuf.cons]).

🔗

explicit basic_ostringstream(
  const basic_string<charT, traits, Allocator>& s,
  ios_base::openmode which = ios_base::out);

Effects: Initializes the base class with basic_ostream<charT, traits>(addressof(sb)) ([ostream]) and sb with basic_stringbuf<charT, traits, Allocator>(s, which | ios_base::out)
([stringbuf.cons]).

🔗

basic_ostringstream(ios_base::openmode which, const Allocator& a);

Effects: Initializes the base class with basic_ostream<charT, traits>(addressof(sb)) ([ostream]) and sb with basic_stringbuf<charT, traits, Allocator>(which | ios_base::out, a)
([stringbuf.cons]).

🔗

explicit basic_ostringstream(
  basic_string<charT, traits, Allocator>&& s,
  ios_base::openmode which = ios_base::out);

Effects: Initializes the base class with basic_ostream<charT, traits>(addressof(sb)) ([ostream]) and sb with basic_stringbuf<charT, traits, Allocator>(std::move(s), which | ios_base::out) ([stringbuf.cons]).

🔗

template<class SAlloc>
  basic_ostringstream(
    const basic_string<charT, traits, SAlloc>& s,
    ios_base::openmode which, const Allocator& a);

Effects: Initializes the base class with basic_ostream<charT, traits>(addressof(sb)) ([ostream]) and sb with basic_stringbuf<charT, traits, Allocator>(s, which | ios_base::out, a)
([stringbuf.cons]).

🔗

template<class SAlloc>
  explicit basic_ostringstream(
    const basic_string<charT, traits, SAlloc>& s,
    ios_base::openmode which = ios_base::out);

Constraints: is_same_v<SAlloc,Allocator> is false.

Effects: Initializes the base class with basic_ostream<charT, traits>(addressof(sb)) ([ostream]) and sb with basic_stringbuf<charT, traits, Allocator>(s, 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.

Then calls basic_ostream<charT, traits>::set_rdbuf(addressof(sb)) to install the contained basic_stringbuf.

29.8.4.2 Assignment and swap [ostringstream.assign]

🔗

void swap(basic_ostringstream& rhs);

Effects: Equivalent to:

basic_ostream<charT, traits>::swap(rhs);
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: Equivalent to: x.swap(y).

29.8.4.3 Member functions [ostringstream.members]

🔗

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

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

🔗

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

Effects: Equivalent to: return rdbuf()->str();

🔗

template<class SAlloc>
  basic_string<charT,traits,SAlloc> str(const SAlloc& sa) const;

Effects: Equivalent to: return rdbuf()->str(sa);

🔗

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

Effects: Equivalent to: return std::move(*rdbuf()).str();

🔗

basic_string_view<charT, traits> view() const noexcept;

Effects: Equivalent to: return rdbuf()->view();

🔗

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

Effects: Equivalent to: rdbuf()->str(s);

🔗

template<class SAlloc>
  void str(const basic_string<charT, traits, SAlloc>& s);

Effects: Equivalent to: rdbuf()->str(s);

🔗

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

Effects: Equivalent to: rdbuf()->str(std::move(s));

29.8.5 Class template basic_stringstream [stringstream]

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

    // [stringstream.cons], constructors
    basic_stringstream() : basic_stringstream(ios_base::out | ios_base::in) {}
    explicit basic_stringstream(ios_base::openmode which);
    explicit basic_stringstream(
      const basic_string<charT, traits, Allocator>& s,
      ios_base::openmode which = ios_base::out | ios_base::in);
    basic_stringstream(ios_base::openmode which, const Allocator& a);
    explicit basic_stringstream(
      basic_string<charT, traits, Allocator>&& s,
      ios_base::openmode which = ios_base::out | ios_base::in);
    template<class SAlloc>
      basic_stringstream(
        const basic_string<charT, traits, SAlloc>& s, const Allocator& a)
        : basic_stringstream(s, ios_base::out | ios_base::in, a) {}
    template<class SAlloc>
      basic_stringstream(
        const basic_string<charT, traits, SAlloc>& s,
        ios_base::openmode which, const Allocator& a);
    template<class SAlloc>
      explicit basic_stringstream(
        const basic_string<charT, traits, SAlloc>& s,
        ios_base::openmode which = ios_base::out | ios_base::in);
    basic_stringstream(const basic_stringstream&) = delete;
    basic_stringstream(basic_stringstream&& rhs);

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

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

    basic_string<charT, traits, Allocator> str() const &;
    template<class SAlloc>
      basic_string<charT,traits,SAlloc> str(const SAlloc& sa) const;
    basic_string<charT, traits, Allocator> str() &&;
    basic_string_view<charT, traits> view() const noexcept;

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

  private:
    basic_stringbuf<charT, traits> sb;  // exposition only
  };

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

The class template basic_stringstream<charT, traits> supports reading and writing from objects of class basic_string<charT, traits, Allocator>.

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

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

(1.1)
sb, the stringbuf object.

29.8.5.1 Constructors [stringstream.cons]

🔗

explicit basic_stringstream(ios_base::openmode which);

Effects: Initializes the base class with basic_iostream<charT, traits>(addressof(sb)) ([iostream.cons]) and sb with basic_stringbuf<charT, traits, Allocator>(which).

🔗

explicit basic_stringstream(
  const basic_string<charT, traits, Allocator>& s,
  ios_base::openmode which = ios_base::out | ios_base::in);

Effects: Initializes the base class with basic_iostream<charT, traits>(addressof(sb)) ([iostream.cons]) and sb with basic_stringbuf<charT, traits, Allocator>(s, which).

🔗

basic_stringstream(ios_base::openmode which, const Allocator& a);

Effects: Initializes the base class with basic_iostream<charT, traits>(addressof(sb)) ([iostream.cons]) and sb with basic_stringbuf<charT, traits, Allocator>(which, a) ([stringbuf.cons]).

🔗

explicit basic_stringstream(
  basic_string<charT, traits, Allocator>&& s,
  ios_base::openmode which = ios_base::out | ios_base::in);

Effects: Initializes the base class with basic_iostream<charT, traits>(addressof(sb)) ([iostream.cons]) and sb with basic_stringbuf<charT, traits, Allocator>(std::move(s), which) ([stringbuf.cons]).

🔗

template<class SAlloc>
  basic_stringstream(
    const basic_string<charT, traits, SAlloc>& s,
    ios_base::openmode which, const Allocator& a);

Effects: Initializes the base class with basic_iostream<charT, traits>(addressof(sb)) ([iostream.cons]) and sb with basic_stringbuf<charT, traits, Allocator>(s, which, a) ([stringbuf.cons]).

🔗

template<class SAlloc>
  explicit basic_stringstream(
    const basic_string<charT, traits, SAlloc>& s,
    ios_base::openmode which = ios_base::out | ios_base::in);

Constraints: is_same_v<SAlloc,Allocator> is false.

Effects: Initializes the base class with basic_iostream<charT, traits>(addressof(sb)) ([iostream.cons]) and sb with basic_stringbuf<charT, traits, Allocator>(s, which) ([stringbuf.cons]).

🔗

basic_stringstream(basic_stringstream&& rhs);

Effects: Move constructs from the rvalue rhs.

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

Then calls basic_istream<charT, traits>::set_rdbuf(addressof(sb)) to install the contained basic_stringbuf.

29.8.5.2 Assignment and swap [stringstream.assign]

🔗

void swap(basic_stringstream& rhs);

Effects: Equivalent to:

basic_iostream<charT,traits>::swap(rhs);
sb.swap(rhs.sb);

🔗

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

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

29.8.5.3 Member functions [stringstream.members]

🔗

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

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

🔗

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

Effects: Equivalent to: return rdbuf()->str();

🔗

template<class SAlloc>
  basic_string<charT,traits,SAlloc> str(const SAlloc& sa) const;

Effects: Equivalent to: return rdbuf()->str(sa);

🔗

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

Effects: Equivalent to: return std::move(*rdbuf()).str();

🔗

basic_string_view<charT, traits> view() const noexcept;

Effects: Equivalent to: return rdbuf()->view();

🔗

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

Effects: Equivalent to: rdbuf()->str(s);

🔗

template<class SAlloc>
  void str(const basic_string<charT, traits, SAlloc>& s);

Effects: Equivalent to: rdbuf()->str(s);

🔗

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

Effects: Equivalent to: rdbuf()->str(std::move(s));

29 Input/output library [input.output]

29.8 String-based streams [string.streams]

29.8.1 Header <sstream> synopsis [sstream.syn]

29.8.2 Class template basic_­stringbuf [stringbuf]

29.8.2.1 Constructors [stringbuf.cons]

29.8.2.2 Assignment and swap [stringbuf.assign]

29.8.2.3 Member functions [stringbuf.members]

29.8.2.4 Overridden virtual functions [stringbuf.virtuals]

29.8.3 Class template basic_­istringstream [istringstream]

29.8.3.1 Constructors [istringstream.cons]

29.8.3.2 Assignment and swap [istringstream.assign]

29.8.3.3 Member functions [istringstream.members]

29.8.4 Class template basic_­ostringstream [ostringstream]

29.8.4.1 Constructors [ostringstream.cons]

29.8.4.2 Assignment and swap [ostringstream.assign]

29.8.4.3 Member functions [ostringstream.members]

29.8.5 Class template basic_­stringstream [stringstream]

29.8.5.1 Constructors [stringstream.cons]

29.8.5.2 Assignment and swap [stringstream.assign]

29.8.5.3 Member functions [stringstream.members]

29.8.2 Class template basic_stringbuf [stringbuf]

29.8.3 Class template basic_istringstream [istringstream]

29.8.4 Class template basic_ostringstream [ostringstream]

29.8.5 Class template basic_stringstream [stringstream]