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[span.streams]
# 31 Input/output library [[input.output]](./#input.output)
## 31.9 Span-based streams [span.streams]
### [31.9.1](#overview) Overview [[span.streams.overview]](span.streams.overview)
[1](#overview-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10001)
The header <spanstream> defines class templates and types
that associate stream buffers with objects whose types are
specializations of span as described in [[views.span]](views.span "23.7.2.2 Class template span")[.](#overview-1.sentence-1)
[*Note [1](#overview-note-1)*:
A user of these classes is responsible for ensuring
that the character sequence represented by the given span outlives the use of the sequence by objects of the classes in [span.streams][.](#overview-1.sentence-2)
Using multiple basic_spanbuf objects
referring to overlapping underlying sequences from different threads,
where at least one basic_spanbuf object is used
for writing to the sequence,
results in a data race[.](#overview-1.sentence-3)
— *end note*]
### [31.9.2](#spanstream.syn) Header <spanstream> synopsis [[spanstream.syn]](spanstream.syn)
[🔗](#lib:spanbuf)
namespace std {// [[spanbuf]](#spanbuf "31.9.3 Class template basic_­spanbuf"), class template basic_spanbuftemplate<class charT, class traits = char_traits<charT>>class basic_spanbuf; template<class charT, class traits>void swap(basic_spanbuf<charT, traits>& x, basic_spanbuf<charT, traits>& y); using spanbuf = basic_spanbuf<char>; using wspanbuf = basic_spanbuf<wchar_t>; // [[ispanstream]](#ispanstream "31.9.4 Class template basic_­ispanstream"), class template basic_ispanstreamtemplate<class charT, class traits = char_traits<charT>>class basic_ispanstream; template<class charT, class traits>void swap(basic_ispanstream<charT, traits>& x, basic_ispanstream<charT, traits>& y); using ispanstream = basic_ispanstream<char>; using wispanstream = basic_ispanstream<wchar_t>; // [[ospanstream]](#ospanstream "31.9.5 Class template basic_­ospanstream"), class template basic_ospanstreamtemplate<class charT, class traits = char_traits<charT>>class basic_ospanstream; template<class charT, class traits>void swap(basic_ospanstream<charT, traits>& x, basic_ospanstream<charT, traits>& y); using ospanstream = basic_ospanstream<char>; using wospanstream = basic_ospanstream<wchar_t>; // [[spanstream]](#spanstream "31.9.6 Class template basic_­spanstream"), class template basic_spanstreamtemplate<class charT, class traits = char_traits<charT>>class basic_spanstream; template<class charT, class traits>void swap(basic_spanstream<charT, traits>& x, basic_spanstream<charT, traits>& y); using spanstream = basic_spanstream<char>; using wspanstream = basic_spanstream<wchar_t>;}
### [31.9.3](#spanbuf) Class template basic_spanbuf [[spanbuf]](spanbuf)
#### [31.9.3.1](#spanbuf.general) General [[spanbuf.general]](spanbuf.general)
[🔗](#lib:basic_spanbuf)
namespace std {template<class charT, class traits = char_traits<charT>>class basic_spanbuf : 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; // [[spanbuf.cons]](#spanbuf.cons "31.9.3.2 Constructors"), constructors basic_spanbuf() : basic_spanbuf(ios_base::in | ios_base::out) {}explicit basic_spanbuf(ios_base::openmode which): basic_spanbuf(std::span<charT>(), which) {}explicit basic_spanbuf(std::span<charT> s,
ios_base::openmode which = ios_base::in | ios_base::out);
basic_spanbuf(const basic_spanbuf&) = delete;
basic_spanbuf(basic_spanbuf&& rhs); // [[spanbuf.assign]](#spanbuf.assign "31.9.3.3 Assignment and swap"), assignment and swap basic_spanbuf& operator=(const basic_spanbuf&) = delete;
basic_spanbuf& operator=(basic_spanbuf&& rhs); void swap(basic_spanbuf& rhs); // [[spanbuf.members]](#spanbuf.members "31.9.3.4 Member functions"), member functions std::span<charT> span() const noexcept; void span(std::span<charT> s) noexcept; protected:// [[spanbuf.virtuals]](#spanbuf.virtuals "31.9.3.5 Overridden virtual functions"), overridden virtual functions 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* std::span<charT> *buf*; // *exposition only*};}
[1](#spanbuf.general-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10120)
The class template basic_spanbuf is derived from basic_streambuf to associate possibly the input sequence and possibly the output sequence
with a sequence of arbitrary characters[.](#spanbuf.general-1.sentence-1)
The sequence is provided by an object of class span<charT>[.](#spanbuf.general-1.sentence-2)
[2](#spanbuf.general-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10126)
For the sake of exposition, the maintained data is presented here as:
- [(2.1)](#spanbuf.general-2.1)
ios_base​::​openmode *mode*, hasin set if the input sequence can be read, andout set if the output sequence can be written[.](#spanbuf.general-2.1.sentence-1)
- [(2.2)](#spanbuf.general-2.2)
std​::​span<charT> *buf* is the view to
the underlying character sequence[.](#spanbuf.general-2.2.sentence-1)
#### [31.9.3.2](#spanbuf.cons) Constructors [[spanbuf.cons]](spanbuf.cons)
[🔗](#lib:basic_spanbuf,constructor)
`explicit basic_spanbuf(std::span<charT> s,
ios_base::openmode which = ios_base::in | ios_base::out);
`
[1](#spanbuf.cons-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10147)
*Effects*: Initializes the base class with basic_streambuf() ([[streambuf.cons]](streambuf.cons "31.6.3.2 Constructors")),
and *mode* with which[.](#spanbuf.cons-1.sentence-1)
Initializes the internal pointers as if calling span(s)[.](#spanbuf.cons-1.sentence-2)
[🔗](#lib:basic_spanbuf,constructor_)
`basic_spanbuf(basic_spanbuf&& rhs);
`
[2](#spanbuf.cons-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10160)
*Effects*: Initializes the base class with std​::​move(rhs) and*mode* with std​::​move(rhs.*mode*) and*buf* with std​::​move(rhs.*buf*)[.](#spanbuf.cons-2.sentence-1)
The sequence pointers in *this (eback(), gptr(), egptr(),pbase(), pptr(), epptr())
obtain the values which rhs had[.](#spanbuf.cons-2.sentence-2)
It isimplementation-defined
whether rhs.*buf*.​empty() returns true after the move[.](#spanbuf.cons-2.sentence-3)
[3](#spanbuf.cons-3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10173)
*Postconditions*: Let rhs_p refer to the state of rhs just prior to this construction[.](#spanbuf.cons-3.sentence-1)
- [(3.1)](#spanbuf.cons-3.1)
span().data() == rhs_p.span().data()
- [(3.2)](#spanbuf.cons-3.2)
span().size() == rhs_p.span().size()
- [(3.3)](#spanbuf.cons-3.3)
eback() == rhs_p.eback()
- [(3.4)](#spanbuf.cons-3.4)
gptr() == rhs_p.gptr()
- [(3.5)](#spanbuf.cons-3.5)
egptr() == rhs_p.egptr()
- [(3.6)](#spanbuf.cons-3.6)
pbase() == rhs_p.pbase()
- [(3.7)](#spanbuf.cons-3.7)
pptr() == rhs_p.pptr()
- [(3.8)](#spanbuf.cons-3.8)
epptr() == rhs_p.epptr()
- [(3.9)](#spanbuf.cons-3.9)
getloc() == rhs_p.getloc()
#### [31.9.3.3](#spanbuf.assign) Assignment and swap [[spanbuf.assign]](spanbuf.assign)
[🔗](#lib:operator=,basic_spanbuf)
`basic_spanbuf& operator=(basic_spanbuf&& rhs);
`
[1](#spanbuf.assign-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10198)
*Effects*: Equivalent to:basic_spanbuf tmp{std::move(rhs)};this->swap(tmp);return *this;
[🔗](#lib:swap,basic_spanbuf)
`void swap(basic_spanbuf& rhs);
`
[2](#spanbuf.assign-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10214)
*Effects*: Equivalent to:basic_streambuf<charT, traits>::swap(rhs);
std::swap(*mode*, rhs.*mode*);
std::swap(*buf*, rhs.*buf*);
[🔗](#lib:swap,basic_spanbuf_)
`template<class charT, class traits>
void swap(basic_spanbuf<charT, traits>& x, basic_spanbuf<charT, traits>& y);
`
[3](#spanbuf.assign-3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10231)
*Effects*: Equivalent to x.swap(y)[.](#spanbuf.assign-3.sentence-1)
#### [31.9.3.4](#spanbuf.members) Member functions [[spanbuf.members]](spanbuf.members)
[🔗](#lib:span,basic_spanbuf)
`std::span<charT> span() const noexcept;
`
[1](#spanbuf.members-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10244)
*Returns*: If ios_base​::​out is set in *mode*,
returns std​::​span<charT>(pbase(), pptr()),
otherwise returns *buf*[.](#spanbuf.members-1.sentence-1)
[*Note [1](#spanbuf.members-note-1)*:
In contrast to basic_stringbuf,
the underlying sequence never grows and is not owned[.](#spanbuf.members-1.sentence-2)
An owning copy can be obtained
by converting the result to basic_string<charT>[.](#spanbuf.members-1.sentence-3)
— *end note*]
[🔗](#lib:span,basic_spanbuf_)
`void span(std::span<charT> s) noexcept;
`
[2](#spanbuf.members-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10264)
*Effects*: *buf* = s[.](#spanbuf.members-2.sentence-1)
Initializes the input and output sequences according to *mode*[.](#spanbuf.members-2.sentence-2)
[3](#spanbuf.members-3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10269)
*Postconditions*:
- [(3.1)](#spanbuf.members-3.1)
If ios_base​::​out is set in *mode*,pbase() == s.data() && epptr() == pbase() + s.size() is true;
* [(3.1.1)](#spanbuf.members-3.1.1)
in addition, if ios_base​::​ate is set in *mode*,pptr() == pbase() + s.size() is true,
* [(3.1.2)](#spanbuf.members-3.1.2)
otherwise pptr() == pbase() is true[.](#spanbuf.members-3.1.sentence-1)
- [(3.2)](#spanbuf.members-3.2)
If ios_base​::​in is set in *mode*,eback() == s.data() && gptr() == eback() && egptr() == eback() + s.size() is true[.](#spanbuf.members-3.2.sentence-1)
#### [31.9.3.5](#spanbuf.virtuals) Overridden virtual functions [[spanbuf.virtuals]](spanbuf.virtuals)
[1](#spanbuf.virtuals-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10292)
[*Note [1](#spanbuf.virtuals-note-1)*:
Because the underlying buffer is of fixed size,
neither overflow, underflow, nor pbackfail can provide useful behavior[.](#spanbuf.virtuals-1.sentence-1)
— *end note*]
[🔗](#lib:seekoff,basic_spanbuf)
`pos_type seekoff(off_type off, ios_base::seekdir way,
ios_base::openmode which = ios_base::in | ios_base::out) override;
`
[2](#spanbuf.virtuals-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10306)
*Effects*: Alters the stream position within one or both of the
controlled sequences, if possible, as follows:
- [(2.1)](#spanbuf.virtuals-2.1)
If ios_base​::​in is set in which, positions the input sequence;xnext is gptr(), xbeg is eback()[.](#spanbuf.virtuals-2.1.sentence-1)
- [(2.2)](#spanbuf.virtuals-2.2)
If ios_base​::​out is set in which, positions the output sequence;xnext is pptr(), xbeg is pbase()[.](#spanbuf.virtuals-2.2.sentence-1)
[3](#spanbuf.virtuals-3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10319)
If both ios_base​::​in and ios_base​::​out are set in which and way is ios_base​::​cur,
the positioning operation fails[.](#spanbuf.virtuals-3.sentence-1)
[4](#spanbuf.virtuals-4)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10324)
For a sequence to be positioned,
if its next pointer xnext (either gptr() or pptr())
is a null pointer and
the new offset newoff as computed below is nonzero,
the positioning operation fails[.](#spanbuf.virtuals-4.sentence-1)
Otherwise, the function determines baseoff as a value of type off_type as follows:
- [(4.1)](#spanbuf.virtuals-4.1)
0 when way is ios_base​::​beg;
- [(4.2)](#spanbuf.virtuals-4.2)
(pptr() - pbase()) for the output sequence, or(gptr() - eback()) for the input sequence
when way is ios_base​::​cur;
- [(4.3)](#spanbuf.virtuals-4.3)
when way is ios_base​::​end :
* [(4.3.1)](#spanbuf.virtuals-4.3.1)
(pptr() - pbase()) if ios_base​::​out is set in *mode* andios_base​::​in is not set in *mode*,
* [(4.3.2)](#spanbuf.virtuals-4.3.2)
*buf*.size() otherwise[.](#spanbuf.virtuals-4.sentence-2)
[5](#spanbuf.virtuals-5)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10351)
If baseoff+off would overflow, or
if baseoff+off is less than zero, or
if baseoff+off is greater than *buf*.size(),
the positioning operation fails[.](#spanbuf.virtuals-5.sentence-1)
Otherwise, the function computesoff_type newoff = baseoff + off; and assigns xbeg + newoff to the next pointer xnext[.](#spanbuf.virtuals-5.sentence-2)
[6](#spanbuf.virtuals-6)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10362)
*Returns*: pos_type(off_type(-1)) if the positioning operation fails;pos_type(newoff) otherwise[.](#spanbuf.virtuals-6.sentence-1)
[🔗](#lib:seekpos,basic_spanbuf)
`pos_type seekpos(pos_type sp, ios_base::openmode which = ios_base::in | ios_base::out) override;
`
[7](#spanbuf.virtuals-7)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10374)
*Effects*: Equivalent to:return seekoff(off_type(sp), ios_base::beg, which);
[🔗](#lib:setbuf,basic_spanbuf)
`basic_streambuf<charT, traits>* setbuf(charT* s, streamsize n) override;
`
[8](#spanbuf.virtuals-8)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10388)
*Effects*: Equivalent to:this->span(std::span<charT>(s, n));return this;
### [31.9.4](#ispanstream) Class template basic_ispanstream [[ispanstream]](ispanstream)
#### [31.9.4.1](#ispanstream.general) General [[ispanstream.general]](ispanstream.general)
[🔗](#lib:basic_ispanstream)
namespace std {template<class charT, class traits = char_traits<charT>>class basic_ispanstream : 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; // [[ispanstream.cons]](#ispanstream.cons "31.9.4.2 Constructors"), constructorsexplicit basic_ispanstream(std::span<charT> s,
ios_base::openmode which = ios_base::in);
basic_ispanstream(const basic_ispanstream&) = delete;
basic_ispanstream(basic_ispanstream&& rhs); template<class ROS> explicit basic_ispanstream(ROS&& s);
basic_ispanstream& operator=(const basic_ispanstream&) = delete;
basic_ispanstream& operator=(basic_ispanstream&& rhs); // [[ispanstream.swap]](#ispanstream.swap "31.9.4.3 Swap"), swapvoid swap(basic_ispanstream& rhs); // [[ispanstream.members]](#ispanstream.members "31.9.4.4 Member functions"), member functions basic_spanbuf<charT, traits>* rdbuf() const noexcept;
std::span<const charT> span() const noexcept; void span(std::span<charT> s) noexcept; template<class ROS> void span(ROS&& s) noexcept; private: basic_spanbuf<charT, traits> *sb*; // *exposition only*};}
[1](#ispanstream.general-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10440)
[*Note [1](#ispanstream.general-note-1)*:
Constructing an ispanstream from a [*string-literal*](lex.string#nt:string-literal "5.13.5 String literals [lex.string]") includes the termination character '\0' in the underlying spanbuf[.](#ispanstream.general-1.sentence-1)
— *end note*]
#### [31.9.4.2](#ispanstream.cons) Constructors [[ispanstream.cons]](ispanstream.cons)
[🔗](#lib:basic_ispanstream,constructor)
`explicit basic_ispanstream(std::span<charT> s, ios_base::openmode which = ios_base::in);
`
[1](#ispanstream.cons-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10455)
*Effects*: Initializes the base class withbasic_istream<charT, traits>(addressof(*sb*)) and *sb* withbasic_spanbuf<charT, traits>(s, which | ios_base​::​in) ([[spanbuf.cons]](#spanbuf.cons "31.9.3.2 Constructors"))[.](#ispanstream.cons-1.sentence-1)
[🔗](#lib:basic_ispanstream,constructor_)
`basic_ispanstream(basic_ispanstream&& rhs);
`
[2](#ispanstream.cons-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10469)
*Effects*: Initializes the base class with std​::​move(rhs) and *sb* with std​::​move(rhs.*sb*)[.](#ispanstream.cons-2.sentence-1)
Next, basic_istream<charT, traits>​::​set_rdbuf(addressof(*sb*)) is called
to install the contained basic_spanbuf[.](#ispanstream.cons-2.sentence-2)
[🔗](#lib:basic_ispanstream,constructor__)
`template<class ROS> explicit basic_ispanstream(ROS&& s)
`
[3](#ispanstream.cons-3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10483)
*Constraints*: ROS models ranges​::​[borrowed_range](range.range#concept:borrowed_range "25.4.2 Ranges [range.range]")[.](#ispanstream.cons-3.sentence-1)
![convertible_to](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_­to [concept.convertible]")<ROS, std​::​span<charT>> && [convertible_to](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_­to [concept.convertible]")<ROS, std​::​span<charT const>> is true[.](#ispanstream.cons-3.sentence-2)
[4](#ispanstream.cons-4)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10489)
*Effects*: Let sp be std​::​span<const charT>(std​::​forward<ROS>(s))[.](#ispanstream.cons-4.sentence-1)
Equivalent to:basic_ispanstream(std::span<charT>(const_cast<charT*>(sp.data()), sp.size()))
#### [31.9.4.3](#ispanstream.swap) Swap [[ispanstream.swap]](ispanstream.swap)
[🔗](#lib:swap,basic_ispanstream)
`void swap(basic_ispanstream& rhs);
`
[1](#ispanstream.swap-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10506)
*Effects*: Equivalent to:basic_istream<charT, traits>::swap(rhs);*sb*.swap(rhs.*sb*);
[🔗](#lib:swap,basic_ispanstream_)
`template<class charT, class traits>
void swap(basic_ispanstream<charT, traits>& x, basic_ispanstream<charT, traits>& y);
`
[2](#ispanstream.swap-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10522)
*Effects*: Equivalent to x.swap(y)[.](#ispanstream.swap-2.sentence-1)
#### [31.9.4.4](#ispanstream.members) Member functions [[ispanstream.members]](ispanstream.members)
[🔗](#lib:rdbuf,basic_ispanstream)
`basic_spanbuf<charT, traits>* rdbuf() const noexcept;
`
[1](#ispanstream.members-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10535)
*Effects*: Equivalent to:return const_cast<basic_spanbuf<charT, traits>*>(addressof(*sb*));
[🔗](#lib:span,basic_ispanstream)
`std::span<const charT> span() const noexcept;
`
[2](#ispanstream.members-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10549)
*Effects*: Equivalent to: return rdbuf()->span();
[🔗](#lib:span,basic_ispanstream_)
`void span(std::span<charT> s) noexcept;
`
[3](#ispanstream.members-3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10560)
*Effects*: Equivalent to rdbuf()->span(s)[.](#ispanstream.members-3.sentence-1)
[🔗](#ispanstream.members-itemdecl:4)
`template<class ROS> void span(ROS&& s) noexcept;
`
[4](#ispanstream.members-4)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10570)
*Constraints*: ROS models ranges​::​[borrowed_range](range.range#concept:borrowed_range "25.4.2 Ranges [range.range]")[.](#ispanstream.members-4.sentence-1)
(![convertible_to](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_­to [concept.convertible]")<ROS, std​::​span<charT>>) && [convertible_to](concept.convertible#concept:convertible_to "18.4.4 Concept convertible_­to [concept.convertible]")<ROS, std​::​span<const charT>> is true[.](#ispanstream.members-4.sentence-2)
[5](#ispanstream.members-5)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10576)
*Effects*: Let sp be std​::​span<const charT>(std​::​forward<ROS>(s))[.](#ispanstream.members-5.sentence-1)
Equivalent to:this->span(std::span<charT>(const_cast<charT*>(sp.data()), sp.size()));
### [31.9.5](#ospanstream) Class template basic_ospanstream [[ospanstream]](ospanstream)
#### [31.9.5.1](#ospanstream.general) General [[ospanstream.general]](ospanstream.general)
[🔗](#lib:basic_ospanstream)
namespace std {template<class charT, class traits = char_traits<charT>>class basic_ospanstream : 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; // [[ospanstream.cons]](#ospanstream.cons "31.9.5.2 Constructors"), constructorsexplicit basic_ospanstream(std::span<charT> s,
ios_base::openmode which = ios_base::out);
basic_ospanstream(const basic_ospanstream&) = delete;
basic_ospanstream(basic_ospanstream&& rhs);
basic_ospanstream& operator=(const basic_ospanstream&) = delete;
basic_ospanstream& operator=(basic_ospanstream&& rhs); // [[ospanstream.swap]](#ospanstream.swap "31.9.5.3 Swap"), swapvoid swap(basic_ospanstream& rhs); // [[ospanstream.members]](#ospanstream.members "31.9.5.4 Member functions"), member functions basic_spanbuf<charT, traits>* rdbuf() const noexcept;
std::span<charT> span() const noexcept; void span(std::span<charT> s) noexcept; private: basic_spanbuf<charT, traits> *sb*; // *exposition only*};}
#### [31.9.5.2](#ospanstream.cons) Constructors [[ospanstream.cons]](ospanstream.cons)
[🔗](#lib:basic_ospanstream,constructor)
`explicit basic_ospanstream(std::span<charT> s,
ios_base::openmode which = ios_base::out);
`
[1](#ospanstream.cons-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10635)
*Effects*: Initializes the base class withbasic_ostream<charT, traits>(addressof(*sb*)) and *sb* withbasic_spanbuf<charT, traits>(s, which | ios_base​::​out) ([[spanbuf.cons]](#spanbuf.cons "31.9.3.2 Constructors"))[.](#ospanstream.cons-1.sentence-1)
[🔗](#lib:basic_ospanstream,constructor_)
`basic_ospanstream(basic_ospanstream&& rhs) noexcept;
`
[2](#ospanstream.cons-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10649)
*Effects*: Initializes the base class with std​::​move(rhs) and *sb* with std​::​move(rhs.*sb*)[.](#ospanstream.cons-2.sentence-1)
Next, basic_ostream<charT, traits>​::​set_rdbuf(addressof(*sb*)) is called to install the contained basic_spanbuf[.](#ospanstream.cons-2.sentence-2)
#### [31.9.5.3](#ospanstream.swap) Swap [[ospanstream.swap]](ospanstream.swap)
[🔗](#lib:swap,basic_ospanstream)
`void swap(basic_ospanstream& rhs);
`
[1](#ospanstream.swap-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10665)
*Effects*: Equivalent to:basic_ostream<charT, traits>::swap(rhs);*sb*.swap(rhs.*sb*);
[🔗](#lib:swap,basic_ospanstream_)
`template<class charT, class traits>
void swap(basic_ospanstream<charT, traits>& x, basic_ospanstream<charT, traits>& y);
`
[2](#ospanstream.swap-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10681)
*Effects*: Equivalent to x.swap(y)[.](#ospanstream.swap-2.sentence-1)
#### [31.9.5.4](#ospanstream.members) Member functions [[ospanstream.members]](ospanstream.members)
[🔗](#lib:rdbuf,basic_ospanstream)
`basic_spanbuf<charT, traits>* rdbuf() const noexcept;
`
[1](#ospanstream.members-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10694)
*Effects*: Equivalent to:return const_cast<basic_spanbuf<charT, traits>*>(addressof(*sb*));
[🔗](#lib:span,basic_ospanstream)
`std::span<charT> span() const noexcept;
`
[2](#ospanstream.members-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10708)
*Effects*: Equivalent to: return rdbuf()->span();
[🔗](#lib:span,basic_ospanstream_)
`void span(std::span<charT> s) noexcept;
`
[3](#ospanstream.members-3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10719)
*Effects*: Equivalent to rdbuf()->span(s)[.](#ospanstream.members-3.sentence-1)
### [31.9.6](#spanstream) Class template basic_spanstream [[spanstream]](spanstream)
#### [31.9.6.1](#spanstream.general) General [[spanstream.general]](spanstream.general)
[🔗](#lib:basic_spanstream)
namespace std {template<class charT, class traits = char_traits<charT>>class basic_spanstream : 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; // [[spanstream.cons]](#spanstream.cons "31.9.6.2 Constructors"), constructorsexplicit basic_spanstream(std::span<charT> s,
ios_base::openmode which = ios_base::out | ios_base::in);
basic_spanstream(const basic_spanstream&) = delete;
basic_spanstream(basic_spanstream&& rhs);
basic_spanstream& operator=(const basic_spanstream&) = delete;
basic_spanstream& operator=(basic_spanstream&& rhs); // [[spanstream.swap]](#spanstream.swap "31.9.6.3 Swap"), swapvoid swap(basic_spanstream& rhs); // [[spanstream.members]](#spanstream.members "31.9.6.4 Member functions"), members basic_spanbuf<charT, traits>* rdbuf() const noexcept;
std::span<charT> span() const noexcept; void span(std::span<charT> s) noexcept; private: basic_spanbuf<charT, traits> *sb*; // *exposition only*};}
#### [31.9.6.2](#spanstream.cons) Constructors [[spanstream.cons]](spanstream.cons)
[🔗](#lib:basic_spanstream,constructor)
`explicit basic_spanstream(std::span<charT> s,
ios_base::openmode which = ios_base::out | ios_bas::in);
`
[1](#spanstream.cons-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10774)
*Effects*: Initializes the base class withbasic_iostream<charT, traits>(addressof(*sb*)) and *sb* withbasic_spanbuf<charT, traits>(s, which) ([[spanbuf.cons]](#spanbuf.cons "31.9.3.2 Constructors"))[.](#spanstream.cons-1.sentence-1)
[🔗](#lib:basic_spanstream,constructor_)
`basic_spanstream(basic_spanstream&& rhs);
`
[2](#spanstream.cons-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10788)
*Effects*: Initializes the base class with std​::​move(rhs) and *sb* with std​::​move(rhs.*sb*)[.](#spanstream.cons-2.sentence-1)
Next, basic_iostream<charT, traits>​::​set_rdbuf(addressof(*sb*)) is called to install the contained basic_spanbuf[.](#spanstream.cons-2.sentence-2)
#### [31.9.6.3](#spanstream.swap) Swap [[spanstream.swap]](spanstream.swap)
[🔗](#lib:swap,basic_spanstream)
`void swap(basic_spanstream& rhs);
`
[1](#spanstream.swap-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10804)
*Effects*: Equivalent to:basic_iostream<charT, traits>::swap(rhs);*sb*.swap(rhs.*sb*);
[🔗](#lib:swap,basic_spanstream_)
`template<class charT, class traits>
void swap(basic_spanstream<charT, traits>& x, basic_spanstream<charT, traits>& y);
`
[2](#spanstream.swap-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10820)
*Effects*: Equivalent to x.swap(y)[.](#spanstream.swap-2.sentence-1)
#### [31.9.6.4](#spanstream.members) Member functions [[spanstream.members]](spanstream.members)
[🔗](#lib:rdbuf,basic_spanstream)
`basic_spanbuf<charT, traits>* rdbuf() const noexcept;
`
[1](#spanstream.members-1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10833)
*Effects*: Equivalent to:return const_cast<basic_spanbuf<charT, traits>*>(addressof(*sb*));
[🔗](#lib:span,basic_spanstream)
`std::span<charT> span() const noexcept;
`
[2](#spanstream.members-2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10847)
*Effects*: Equivalent to: return rdbuf()->span();
[🔗](#lib:span,basic_spanstream_)
`void span(std::span<charT> s) noexcept;
`
[3](#spanstream.members-3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L10858)
*Effects*: Equivalent to rdbuf()->span(s)[.](#spanstream.members-3.sentence-1)
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