cppdraft_translate/cppdraft/syncstream.md

[syncstream]

# 31 Input/output library [[input.output]](./#input.output)

## 31.11 Synchronized output streams [syncstream]

### [31.11.1](#syn) Header <syncstream> synopsis [[syncstream.syn]](syncstream.syn)

[ð](#header:%3csyncstream%3e)

#include <ostream> // see [[ostream.syn]](ostream.syn "31.7.2 Header <ostream> synopsis")namespace std {// [[syncstream.syncbuf]](#syncbuf "31.11.2 Class template basic_syncbuf"), class template basic_syncbuftemplate<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>>class basic_syncbuf; // [[syncstream.syncbuf.special]](#syncbuf.special "31.11.2.6 Specialized algorithms"), specialized algorithmstemplate<class charT, class traits, class Allocator>void swap(basic_syncbuf<charT, traits, Allocator>&,
 basic_syncbuf<charT, traits, Allocator>&); using syncbuf = basic_syncbuf<char>; using wsyncbuf = basic_syncbuf<wchar_t>; // [[syncstream.osyncstream]](#osyncstream "31.11.3 Class template basic_osyncstream"), class template basic_osyncstreamtemplate<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>>class basic_osyncstream; using osyncstream = basic_osyncstream<char>; using wosyncstream = basic_osyncstream<wchar_t>;}

[1](#syn-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12596)

The header [<syncstream>](#header:%3csyncstream%3e "31.11.1 Header <syncstream> synopsis [syncstream.syn]") provides a mechanism
to synchronize execution agents writing to the same stream[.](#syn-1.sentence-1)

### [31.11.2](#syncbuf) Class template basic_syncbuf [[syncstream.syncbuf]](syncstream.syncbuf)

#### [31.11.2.1](#syncbuf.overview) Overview [[syncstream.syncbuf.overview]](syncstream.syncbuf.overview)

[ð](#lib:basic_syncbuf)

namespace std {template<class charT, class traits = char_traits<charT>, class Allocator = allocator<charT>>class basic_syncbuf : 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; using streambuf_type = basic_streambuf<charT, traits>; // [[syncstream.syncbuf.cons]](#syncbuf.cons "31.11.2.2 Construction and destruction"), construction and destruction basic_syncbuf(): basic_syncbuf(nullptr) {}explicit basic_syncbuf(streambuf_type* obuf): basic_syncbuf(obuf, Allocator()) {} basic_syncbuf(streambuf_type*, const Allocator&);
 basic_syncbuf(basic_syncbuf&&); ~basic_syncbuf(); // [[syncstream.syncbuf.assign]](#syncbuf.assign "31.11.2.3 Assignment and swap"), assignment and swap basic_syncbuf& operator=(basic_syncbuf&&); void swap(basic_syncbuf&); // [[syncstream.syncbuf.members]](#syncbuf.members "31.11.2.4 Member functions"), member functionsbool emit();
 streambuf_type* get_wrapped() const noexcept;
 allocator_type get_allocator() const noexcept; void set_emit_on_sync(bool) noexcept; protected:// [[syncstream.syncbuf.virtuals]](#syncbuf.virtuals "31.11.2.5 Overridden virtual functions"), overridden virtual functionsint sync() override; private: streambuf_type* *wrapped*; // *exposition only*bool *emit-on-sync*{}; // *exposition only*};}

[1](#syncbuf.overview-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12649)

Class template basic_syncbuf stores character data
written to it, known as the associated output, into internal
buffers allocated using the object's allocator[.](#syncbuf.overview-1.sentence-1)

The associated output is transferred to the
wrapped stream buffer object **wrapped* when emit() is called
or when the basic_syncbuf object is destroyed[.](#syncbuf.overview-1.sentence-2)

Such transfers are atomic with respect to transfers
by other basic_syncbuf objects
with the same wrapped stream buffer object[.](#syncbuf.overview-1.sentence-3)

#### [31.11.2.2](#syncbuf.cons) Construction and destruction [[syncstream.syncbuf.cons]](syncstream.syncbuf.cons)

[ð](#lib:basic_syncbuf,constructor)

`basic_syncbuf(streambuf_type* obuf, const Allocator& allocator);
`

[1](#syncbuf.cons-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12669)

*Effects*: Sets *wrapped* to obuf[.](#syncbuf.cons-1.sentence-1)

[2](#syncbuf.cons-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12673)

*Postconditions*: get_wrapped() == obuf andget_allocator() == allocator are true[.](#syncbuf.cons-2.sentence-1)

[3](#syncbuf.cons-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12678)

*Throws*: Nothing unless an exception is thrown
by the construction of a mutex or
by memory allocation[.](#syncbuf.cons-3.sentence-1)

[4](#syncbuf.cons-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12684)

*Remarks*: A copy of allocator is used
to allocate memory for internal buffers
holding the associated output[.](#syncbuf.cons-4.sentence-1)

[ð](#lib:basic_syncbuf,constructor_)

`basic_syncbuf(basic_syncbuf&& other);
`

[5](#syncbuf.cons-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12697)

*Postconditions*: The value returned by this->get_wrapped() is the value returned by other.get_wrapped() prior to calling this constructor[.](#syncbuf.cons-5.sentence-1)

Output stored in other prior to calling this constructor
will be stored in *this afterwards[.](#syncbuf.cons-5.sentence-2)

other.pbase() == other.pptr() andother.get_wrapped() == nullptr are true[.](#syncbuf.cons-5.sentence-3)

[6](#syncbuf.cons-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12710)

*Remarks*: This constructor disassociates other from its wrapped stream buffer,
ensuring destruction of other produces no output[.](#syncbuf.cons-6.sentence-1)

[ð](#lib:basic_syncbuf,destructor)

`~basic_syncbuf();
`

[7](#syncbuf.cons-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12723)

*Effects*: Calls emit()[.](#syncbuf.cons-7.sentence-1)

[8](#syncbuf.cons-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12727)

*Throws*: Nothing[.](#syncbuf.cons-8.sentence-1)

If an exception is thrown from emit(),
the destructor catches and ignores that exception[.](#syncbuf.cons-8.sentence-2)

#### [31.11.2.3](#syncbuf.assign) Assignment and swap [[syncstream.syncbuf.assign]](syncstream.syncbuf.assign)

[ð](#lib:operator=,basic_syncbuf)

`basic_syncbuf& operator=(basic_syncbuf&& rhs);
`

[1](#syncbuf.assign-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12742)

*Effects*: Calls emit() then
move assigns from rhs[.](#syncbuf.assign-1.sentence-1)

After the move assignment *this has the observable state it would have had if
it had been move constructed from rhs ([[syncstream.syncbuf.cons]](#syncbuf.cons "31.11.2.2 Construction and destruction"))[.](#syncbuf.assign-1.sentence-2)

[2](#syncbuf.assign-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12750)

*Postconditions*:

- [(2.1)](#syncbuf.assign-2.1)

rhs.get_wrapped() == nullptr is true.

- [(2.2)](#syncbuf.assign-2.2)

this->get_allocator() == rhs.get_allocator() is true whenallocator_traits<Allocator>::propagate_on_container_move_assignment::value is true; otherwise, the allocator is unchanged.

[3](#syncbuf.assign-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12763)

*Returns*: *this[.](#syncbuf.assign-3.sentence-1)

[4](#syncbuf.assign-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12767)

*Remarks*: This assignment operator disassociates rhs from its wrapped stream buffer,
ensuring destruction of rhs produces no output[.](#syncbuf.assign-4.sentence-1)

[ð](#lib:swap,basic_syncbuf)

`void swap(basic_syncbuf& other);
`

[5](#syncbuf.assign-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12780)

*Preconditions*: Eitherallocator_traits<Allocator>::propagate_on_container_swap::value is true orthis->get_allocator() == other.get_allocator() is true[.](#syncbuf.assign-5.sentence-1)

[6](#syncbuf.assign-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12789)

*Effects*: Exchanges the state of *this and other[.](#syncbuf.assign-6.sentence-1)

#### [31.11.2.4](#syncbuf.members) Member functions [[syncstream.syncbuf.members]](syncstream.syncbuf.members)

[ð](#lib:emit,basic_syncbuf)

`bool emit();
`

[1](#syncbuf.members-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12802)

*Effects*: Atomically transfers the associated output of *this to the stream buffer **wrapped*,
so that it appears in the output stream
as a contiguous sequence of characters[.](#syncbuf.members-1.sentence-1)

*wrapped*->pubsync() is called
if and only if a call was made to sync() since the most recent call to emit(), if any[.](#syncbuf.members-1.sentence-2)

[2](#syncbuf.members-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12812)

*Synchronization*: All emit() calls transferring characters
to the same stream buffer object
appear to execute in a total order
consistent with the âhappens beforeâ relation ([[intro.races]](intro.races "6.10.2.2 Data races")),
where each emit() call
synchronizes with
subsequent emit() calls in that total order[.](#syncbuf.members-2.sentence-1)

[3](#syncbuf.members-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12822)

*Postconditions*: On success, the associated output is empty[.](#syncbuf.members-3.sentence-1)

[4](#syncbuf.members-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12826)

*Returns*: true if all of the following conditions hold;
otherwise false:

- [(4.1)](#syncbuf.members-4.1)

  *wrapped* == nullptr is false[.](#syncbuf.members-4.1.sentence-1)

- [(4.2)](#syncbuf.members-4.2)

  All of the characters in the associated output were successfully transferred[.](#syncbuf.members-4.2.sentence-1)

- [(4.3)](#syncbuf.members-4.3)

  The call to *wrapped*->pubsync() (if any) succeeded[.](#syncbuf.members-4.3.sentence-1)

[5](#syncbuf.members-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12836)

*Remarks*: May call member functions of *wrapped* while holding a lock uniquely associated with *wrapped*[.](#syncbuf.members-5.sentence-1)

[ð](#lib:get_wrapped,basic_syncbuf)

`streambuf_type* get_wrapped() const noexcept;
`

[6](#syncbuf.members-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12848)

*Returns*: *wrapped*[.](#syncbuf.members-6.sentence-1)

[ð](#lib:get_allocator,basic_syncbuf)

`allocator_type get_allocator() const noexcept;
`

[7](#syncbuf.members-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12859)

*Returns*: A copy of the allocator that was set in the constructor or assignment operator[.](#syncbuf.members-7.sentence-1)

[ð](#lib:set_emit_on_sync,basic_syncbuf)

`void set_emit_on_sync(bool b) noexcept;
`

[8](#syncbuf.members-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12870)

*Effects*: *emit-on-sync* = b[.](#syncbuf.members-8.sentence-1)

#### [31.11.2.5](#syncbuf.virtuals) Overridden virtual functions [[syncstream.syncbuf.virtuals]](syncstream.syncbuf.virtuals)

[ð](#lib:sync,basic_syncbuf)

`int sync() override;
`

[1](#syncbuf.virtuals-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12883)

*Effects*: Records that the wrapped stream buffer is to be flushed[.](#syncbuf.virtuals-1.sentence-1)

Then, if *emit-on-sync* is true, calls emit()[.](#syncbuf.virtuals-1.sentence-2)

[*Note [1](#syncbuf.virtuals-note-1)*:

If *emit-on-sync* is false,
the actual flush is delayed until a call to emit()[.](#syncbuf.virtuals-1.sentence-3)

â *end note*]

[2](#syncbuf.virtuals-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12892)

*Returns*: If emit() was called and returned false,
returns -1; otherwise 0[.](#syncbuf.virtuals-2.sentence-1)

#### [31.11.2.6](#syncbuf.special) Specialized algorithms [[syncstream.syncbuf.special]](syncstream.syncbuf.special)

[ð](#lib:swap,basic_syncbuf_)

`template<class charT, class traits, class Allocator>
  void swap(basic_syncbuf<charT, traits, Allocator>& a,
            basic_syncbuf<charT, traits, Allocator>& b);
`

[1](#syncbuf.special-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12908)

*Effects*: Equivalent to a.swap(b)[.](#syncbuf.special-1.sentence-1)

### [31.11.3](#osyncstream) Class template basic_osyncstream [[syncstream.osyncstream]](syncstream.osyncstream)

#### [31.11.3.1](#osyncstream.overview) Overview [[syncstream.osyncstream.overview]](syncstream.osyncstream.overview)

[ð](#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]](#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]](#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](#osyncstream.overview-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"))[.](#osyncstream.overview-1.sentence-1)

[2](#osyncstream.overview-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12962)

[*Example [1](#osyncstream.overview-example-1)*:

A named variable can be used within a block statement for streaming[.](#osyncstream.overview-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 â *end example*]

[3](#osyncstream.overview-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12976)

[*Example [2](#osyncstream.overview-example-2)*:

A temporary object can be used for streaming within a single statement[.](#osyncstream.overview-3.sentence-1)

osyncstream(cout) << "Hello, " << "World!" << '\n';

In this example, cout is not flushed[.](#osyncstream.overview-3.sentence-2)

â *end example*]

#### [31.11.3.2](#osyncstream.cons) Construction and destruction [[syncstream.osyncstream.cons]](syncstream.osyncstream.cons)

[ð](#lib:basic_osyncstream,constructor)

`basic_osyncstream(streambuf_type* buf, const Allocator& allocator);
`

[1](#osyncstream.cons-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12993)

*Effects*: Initializes *sb* from buf and allocator[.](#osyncstream.cons-1.sentence-1)

Initializes the base class with basic_ostream<charT, traits>(addressof(*sb*))[.](#osyncstream.cons-1.sentence-2)

[2](#osyncstream.cons-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L12998)

[*Note [1](#osyncstream.cons-note-1)*:

The member functions of the provided stream buffer
can be called from emit() while a lock is held,
which might result in a deadlock if used incautiously[.](#osyncstream.cons-2.sentence-1)

â *end note*]

[3](#osyncstream.cons-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L13005)

*Postconditions*: get_wrapped() == buf is true[.](#osyncstream.cons-3.sentence-1)

[ð](#lib:basic_osyncstream,constructor_)

`basic_osyncstream(basic_osyncstream&& other) noexcept;
`

[4](#osyncstream.cons-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L13016)

*Effects*: Move constructs the base class
and *sb* from the corresponding subobjects of other,
and calls basic_ostream<charT, traits>::set_rdbuf(addressof(*sb*))[.](#osyncstream.cons-4.sentence-1)

[5](#osyncstream.cons-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L13022)

*Postconditions*: The value returned by get_wrapped() is the value returned by other.get_wrapped() prior to calling this constructor[.](#osyncstream.cons-5.sentence-1)

nullptr == other.get_wrapped() is true[.](#osyncstream.cons-5.sentence-2)

#### [31.11.3.3](#osyncstream.members) Member functions [[syncstream.osyncstream.members]](syncstream.osyncstream.members)

[ð](#lib:set_emit_on_sync,basic_osyncstream)

`void emit();
`

[1](#osyncstream.members-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L13038)

*Effects*: Behaves as an unformatted output function ([[ostream.unformatted]](ostream.unformatted "31.7.6.4 Unformatted output functions"))[.](#osyncstream.members-1.sentence-1)

After constructing a sentry object, calls *sb*.emit()[.](#osyncstream.members-1.sentence-2)

If that call returns false,
calls setstate(ios_base::badbit)[.](#osyncstream.members-1.sentence-3)

[2](#osyncstream.members-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L13045)

[*Example [1](#osyncstream.members-example-1)*:

A flush on a basic_osyncstream does not flush immediately:{ osyncstream bout(cout);
 bout << "Hello," << '\n'; // no flush bout.emit(); // characters transferred; cout not flushed bout << "World!" << endl; // flush noted; cout not flushed bout.emit(); // characters transferred; cout flushed bout << "Greetings." << '\n'; // no flush} // characters transferred; cout not flushed

â *end example*]

[3](#osyncstream.members-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L13060)

[*Example [2](#osyncstream.members-example-2)*:

The function emit() can be used to
handle exceptions from operations on the underlying stream[.](#osyncstream.members-3.sentence-1)

{ osyncstream bout(cout);
 bout << "Hello, " << "World!" << '\n'; try { bout.emit(); } catch (...) {// handle exception}} â *end example*]

[ð](#lib:set_emit_on_sync,basic_osyncstream_)

`streambuf_type* get_wrapped() const noexcept;
`

[4](#osyncstream.members-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L13084)

*Returns*: *sb*.get_wrapped()[.](#osyncstream.members-4.sentence-1)

[5](#osyncstream.members-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L13088)

[*Example [3](#osyncstream.members-example-3)*:

Obtaining the wrapped stream buffer with get_wrapped() allows wrapping it again with an osyncstream[.](#osyncstream.members-5.sentence-1)

For example,{ osyncstream bout1(cout);
 bout1 << "Hello, "; { osyncstream(bout1.get_wrapped()) << "Goodbye, " << "Planet!" << '\n'; } bout1 << "World!" << '\n';} produces the *uninterleaved* output

```
Goodbye, Planet!
Hello, World!

```

â *end example*]