31 Input/output library [input.output]

31.8 String-based streams [string.streams]

31.8.2 Class template basic_stringbuf [stringbuf] 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.
  • If ios_base​::​out is set in mode, pbase() points to buf.front() and epptr() >= pbase() + buf.size() is true;
    • in addition, if ios_base​::​ate is set in mode, pptr() == pbase() + buf.size() is true,
    • otherwise pptr() == pbase() is true.
  • If ios_base​::​in is set in mode, eback() points to buf.front(), and (gptr() == eback() && egptr() == eback() + buf.size()) is true.
[Note 1: 
For efficiency reasons, stream buffer operations can 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.reqmts]).
Effects: Equivalent to: return basic_string<charT, traits, SAlloc>(view(), sa);
basic_string<charT, traits, Allocator> str() &&;
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.
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().
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:
  • If ios_base​::​out is set in mode, then sv(pbase(), high_mark-pbase()) is returned.
  • Otherwise, if ios_base​::​in is set in mode, then sv(eback(), egptr()-eback()) is returned.
  • Otherwise, sv() is returned.
[Note 2: 
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();
template<class T> void str(const T& t);
Constraints: is_convertible_v<const T&, basic_string_view<charT, traits>> is true.
Effects: Equivalent to: basic_string_view<charT, traits> sv = t; buf = sv; init_buf_ptrs();