[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 "31.11.3.2 Construction 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 "31.11.3.3 Member 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 "16.4.4.6.1 General [allocator.requirements.general]") requirements ([[allocator.requirements.general]](allocator.requirements.general "16.4.4.6.1 General"))[.](#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*]