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
explicit basic_stringbuf(
ios_base::openmode which = ios_base::in | ios_base::out);
explicit basic_stringbuf(
const basic_string<charT, traits, Allocator>& str,
ios_base::openmode which = ios_base::in | ios_base::out);
basic_stringbuf(const basic_stringbuf& rhs) = delete;
basic_stringbuf(basic_stringbuf&& rhs);
// [stringbuf.assign], assign and swap
basic_stringbuf& operator=(const basic_stringbuf& rhs) = delete;
basic_stringbuf& operator=(basic_stringbuf&& rhs);
void swap(basic_stringbuf& rhs);
// [stringbuf.members], get and set
basic_string<charT, traits, Allocator> str() const;
void str(const 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
};
template <class charT, class traits, class Allocator>
void swap(basic_stringbuf<charT, traits, Allocator>& x,
basic_stringbuf<charT, traits, Allocator>& 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 is presented here as:
ios_base::openmode mode, has in set if the input sequence can be read, and out set if the output sequence can be written.
explicit basic_stringbuf(
ios_base::openmode which = ios_base::in | ios_base::out);
Effects: Constructs an object of class basic_stringbuf, initializing the base class with basic_streambuf() ([streambuf.cons]), and initializing mode with which.
explicit basic_stringbuf(
const basic_string<charT, traits, Allocator>& s,
ios_base::openmode which = ios_base::in | ios_base::out);
Effects: Constructs an object of class basic_stringbuf, initializing the base class with basic_streambuf() ([streambuf.cons]), and initializing mode with which. Then calls str(s).
basic_stringbuf(basic_stringbuf&& rhs);
Effects: Move constructs from the rvalue rhs. It is implementation-defined whether the sequence pointers in *this (eback(), gptr(), egptr(), pbase(), pptr(), epptr()) obtain the values which rhs had. Whether they do or not, *this and rhs reference separate buffers (if any at all) after the construction. The openmode, locale and any other state of rhs is also copied.
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.
str() == rhs_p.str()
gptr() - eback() == rhs_p.gptr() - rhs_p.eback()
egptr() - eback() == rhs_p.egptr() - rhs_p.eback()
pptr() - pbase() == rhs_p.pptr() - rhs_p.pbase()
epptr() - pbase() == rhs_p.epptr() - rhs_p.pbase()
if (eback()) eback() != rhs_a.eback()
if (gptr()) gptr() != rhs_a.gptr()
if (egptr()) egptr() != rhs_a.egptr()
if (pbase()) pbase() != rhs_a.pbase()
if (pptr()) pptr() != rhs_a.pptr()
if (epptr()) epptr() != rhs_a.epptr()
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]).
void swap(basic_stringbuf& rhs);
template <class charT, class traits, class Allocator>
void swap(basic_stringbuf<charT, traits, Allocator>& x,
basic_stringbuf<charT, traits, Allocator>& y);
basic_string<charT, traits, Allocator> str() const;
Returns: A basic_string object whose content is equal to the basic_stringbuf underlying character sequence. If the basic_stringbuf was created only in input mode, the resultant basic_string contains the character sequence in the range [eback(), egptr()). If the basic_stringbuf was created with which & ios_base::out being nonzero then the resultant basic_string contains the character sequence in the range [pbase(), high_mark), 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 with a basic_string, or by calling the str(basic_string) member function. In the case of calling the str(basic_string) member function, all characters initialized prior to the call are now considered uninitialized (except for those characters re-initialized by the new basic_string). Otherwise the basic_stringbuf has been created in neither input nor output mode and a zero length basic_string is returned.
void str(const basic_string<charT, traits, Allocator>& s);
Effects: Copies the content of s into the basic_stringbuf underlying character sequence and initializes the input and output sequences according to mode.
Postconditions: If mode & ios_base::out is nonzero, pbase() points to the first underlying character and epptr() >= pbase() + s.size() holds; in addition, if mode & ios_base::ate is nonzero, pptr() == pbase() + s.size() holds, otherwise pptr() == pbase() is true. If mode & ios_base::in is nonzero, eback() points to the first underlying character, and both gptr() == eback() and egptr() == eback() + s.size() hold.
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:
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.
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.
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).
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:
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.
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().
The function can make a write position available only if (mode & ios_base::out) != 0. 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 (mode & ios_base::in) != 0, 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 115.
| Conditions | Result |
| (which & ios_base::in) == ios_base::in | positions the input sequence |
| (which & ios_base::out) == ios_base::out | positions the output sequence |
|
(which & (ios_base::in | ios_base::out)) == (ios_base::in) | ios_base::out)) and way == either ios_base::beg or ios_base::end | positions both the input and the output sequences |
| Otherwise | the positioning operation fails. |
For a sequence to be positioned, if its next pointer (either gptr() or pptr()) is a null pointer and the new offset newoff is nonzero, the positioning operation fails. Otherwise, the function determines newoff as indicated in Table 116.
| 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;
basic_streambuf<charT, traits>* setbuf(charT* s, streamsize n);