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[syncstream.osyncstream.overview]
# 31 Input/output library [[input.output]](./#input.output)
## 31.11 Synchronized output streams [[syncstream]](syncstream#osyncstream.overview)
### 31.11.3 Class template basic_osyncstream [[syncstream.osyncstream]](syncstream.osyncstream#overview)
#### 31.11.3.1 Overview [syncstream.osyncstream.overview]
[🔗](#lib:basic_osyncstream)
namespace std {template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>>class basic_osyncstream : 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; using streambuf_type = basic_streambuf<charT, traits>; using syncbuf_type = basic_syncbuf<charT, traits, Allocator>; // [[syncstream.osyncstream.cons]](syncstream.osyncstream.cons "31.11.3.2Construction and destruction"), construction and destruction basic_osyncstream(streambuf_type*, const Allocator&); explicit basic_osyncstream(streambuf_type* obuf): basic_osyncstream(obuf, Allocator()) {} basic_osyncstream(basic_ostream<charT, traits>& os, const Allocator& allocator): basic_osyncstream(os.rdbuf(), allocator) {}explicit basic_osyncstream(basic_ostream<charT, traits>& os): basic_osyncstream(os, Allocator()) {} basic_osyncstream(basic_osyncstream&&) noexcept; ~basic_osyncstream(); // assignment basic_osyncstream& operator=(basic_osyncstream&&); // [[syncstream.osyncstream.members]](syncstream.osyncstream.members "31.11.3.3Member functions"), member functionsvoid emit();
streambuf_type* get_wrapped() const noexcept;
syncbuf_type* rdbuf() const noexcept { return const_cast<syncbuf_type*>(addressof(*sb*)); }private: syncbuf_type *sb*; // *exposition only*};}
[1](#1)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12958)
Allocator shall meet
the [*Cpp17Allocator*](allocator.requirements.general#:Cpp17Allocator "16.4.4.6.1General[allocator.requirements.general]") requirements ([[allocator.requirements.general]](allocator.requirements.general "16.4.4.6.1General"))[.](#1.sentence-1)
[2](#2)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12962)
[*Example [1](#example-1)*:
A named variable can be used within a block statement for streaming[.](#2.sentence-1)
{ osyncstream bout(cout);
bout << "Hello, ";
bout << "World!";
bout << endl; // flush is noted bout << "and more!\n";} // characters are transferred and cout is flushed — *end example*]
[3](#3)
[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12976)
[*Example [2](#example-2)*:
A temporary object can be used for streaming within a single statement[.](#3.sentence-1)
osyncstream(cout) << "Hello, " << "World!" << '\n';
In this example, cout is not flushed[.](#3.sentence-2)
— *end example*]