std::basic_syncbuf

 

C++

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Feature test macros (C++20)

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Technical specifications

Symbols index

External libraries

 

Input/output library

I/O manipulators

Print functions (C++23)

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

basic_spanbuf (C++23)

strstreambuf (C++98/26*)

basic_syncbuf (C++20)

Streams

Abstractions

ios_base

basic_ios

basic_istream

basic_ostream

basic_iostream

File I/O

basic_ifstream

basic_ofstream

basic_fstream

String I/O

basic_istringstream

basic_ostringstream

basic_stringstream

Array I/O

basic_ispanstream (C++23)

basic_ospanstream (C++23)

basic_spanstream (C++23)

istrstream (C++98/26*)

ostrstream (C++98/26*)

strstream (C++98/26*)

Synchronized Output

basic_osyncstream (C++20)

Types

streamoff

streamsize

fpos

Error category interface

iostream_category (C++11)

io_errc (C++11)

 

std::basic_syncbuf

Public member functions

basic_syncbuf::basic_syncbuf (C++20)

basic_syncbuf::operator= (C++20)

basic_syncbuf::~basic_syncbuf (C++20)

basic_syncbuf::swap (C++20)

basic_syncbuf::emit (C++20)

basic_syncbuf::get_wrapped (C++20)

basic_syncbuf::get_allocator (C++20)

basic_syncbuf::set_emit_on_sync (C++20)

Protected member functions

basic_syncbuf::sync (C++20)

Non-member functions

swap(std::basic_syncbuf) (C++20)

 

Defined in header <syncstream>
template<     class CharT,     class Traits = std::char_traits<CharT>,     class Allocator = std::allocator<CharT> > class basic_syncbuf : public std::basic_streambuf<CharT, Traits>		(since C++20)

std::basic_syncbuf is a wrapper for a std::basic_streambuf (provided at construction time as a pointer). It accumulates output in its own internal buffer, and atomically transmits its entire contents to the wrapped buffer on destruction and when explicitly requested, so that they appear as a contiguous sequence of characters. It guarantees that there are no data races and no interleaving of characters sent to the wrapped buffer as long as all other outputs made to the same buffer are made through, possibly different, instances of std::basic_syncbuf.

Typical implementation of std::basic_syncbuf holds a pointer to the wrapped std::basic_streambuf, a boolean flag indicating whether the buffer will transmit its contents to the wrapped buffer on sync (flush), a boolean flag indicating a pending flush when the policy is to not emit on sync, an internal buffer that uses Allocator (such as std::string), and a pointer to a mutex used to synchronize emit between multiple threads accessing the same wrapped stream buffer (these mutexes may be in a hash map with pointers to std::basic_streambuf objects used as keys).

Like other streambuf classes, std::basic_syncbuf is normally only accessed through the corresponding stream, std::osyncstream, not directly.

Several typedefs for common character types are provided:

Defined in header <syncstream>
Type	Definition
std::syncbuf	std::basic_syncbuf<char>
std::wsyncbuf	std::basic_syncbuf<wchar_t>

Member types

Member type	Definition
char_type	CharT
traits_type	Traits; the program is ill-formed if Traits::char_type is not CharT.
int_type	Traits::int_type
pos_type	Traits::pos_type
off_type	Traits::off_type
allocator_type	Allocator
streambuf_type	std::basic_streambuf<CharT, Traits>

Member functions

Public member functions
(constructor)	constructs a basic_syncbuf object (public member function)
operator=	assigns a basic_syncbuf object (public member function)
swap	swaps two basic_syncbuf objects (public member function)
(destructor)	destroys the basic_syncbuf and emits its internal buffer (public member function)
emit	atomically transmits the entire internal buffer to the wrapped streambuf (public member function)
get_wrapped	retrieves the wrapped streambuf pointer (public member function)
get_allocator	retrieves the allocator used by this basic_syncbuf (public member function)
set_emit_on_sync	changes the current emit-on-sync policy (public member function)
Protected member functions
sync	either emits, or records a pending flush, depending on the current emit-on-sync policy (public member function)

Non-member functions

std::swap(std::basic_syncbuf) (C++20)

specializes the std::swap algorithm (function template)

Inherited from std::basic_streambuf

Member types

Member type	Definition
char_type	CharT
traits_type	Traits; the program is ill-formed if Traits::char_type is not CharT.
int_type	Traits::int_type
pos_type	Traits::pos_type
off_type	Traits::off_type

Member functions

(destructor) [virtual]	destructs the basic_streambuf object (virtual public member function of std::basic_streambuf<CharT,Traits>)
Locales
pubimbue	invokes imbue() (public member function of std::basic_streambuf<CharT,Traits>)
getloc	obtains a copy of the associated locale (public member function of std::basic_streambuf<CharT,Traits>)
Positioning
pubsetbuf	invokes setbuf() (public member function of std::basic_streambuf<CharT,Traits>)
pubseekoff	invokes seekoff() (public member function of std::basic_streambuf<CharT,Traits>)
pubseekpos	invokes seekpos() (public member function of std::basic_streambuf<CharT,Traits>)
pubsync	invokes sync() (public member function of std::basic_streambuf<CharT,Traits>)
Get area
in_avail	obtains the number of characters immediately available in the get area (public member function of std::basic_streambuf<CharT,Traits>)
snextc	advances the input sequence, then reads one character without advancing again (public member function of std::basic_streambuf<CharT,Traits>)
sbumpcstossc (removed in C++17)	reads one character from the input sequence and advances the sequence (public member function of std::basic_streambuf<CharT,Traits>)
sgetc	reads one character from the input sequence without advancing the sequence (public member function of std::basic_streambuf<CharT,Traits>)
sgetn	invokes xsgetn() (public member function of std::basic_streambuf<CharT,Traits>)
Put area
sputc	writes one character to the put area and advances the next pointer (public member function of std::basic_streambuf<CharT,Traits>)
sputn	invokes xsputn() (public member function of std::basic_streambuf<CharT,Traits>)
Putback
sputbackc	puts one character back in the input sequence (public member function of std::basic_streambuf<CharT,Traits>)
sungetc	moves the next pointer in the input sequence back by one (public member function of std::basic_streambuf<CharT,Traits>)

Protected member functions

(constructor)	constructs a basic_streambuf object (protected member function)
operator= (C++11)	replaces a basic_streambuf object (protected member function)
swap (C++11)	swaps two basic_streambuf objects (protected member function)
Locales
imbue [virtual]	changes the associated locale (virtual protected member function of std::basic_streambuf<CharT,Traits>)
Positioning
setbuf [virtual]	replaces the buffer with user-defined array, if permitted (virtual protected member function of std::basic_streambuf<CharT,Traits>)
seekoff [virtual]	repositions the next pointer in the input sequence, output sequence, or both, using relative addressing (virtual protected member function of std::basic_streambuf<CharT,Traits>)
seekpos [virtual]	repositions the next pointer in the input sequence, output sequence, or both using absolute addressing (virtual protected member function of std::basic_streambuf<CharT,Traits>)
sync [virtual]	synchronizes the buffers with the associated character sequence (virtual protected member function of std::basic_streambuf<CharT,Traits>)
Get area
showmanyc [virtual]	obtains the number of characters available for input in the associated input sequence, if known (virtual protected member function of std::basic_streambuf<CharT,Traits>)
underflow [virtual]	reads characters from the associated input sequence to the get area (virtual protected member function of std::basic_streambuf<CharT,Traits>)
uflow [virtual]	reads characters from the associated input sequence to the get area and advances the next pointer (virtual protected member function of std::basic_streambuf<CharT,Traits>)
xsgetn [virtual]	reads multiple characters from the input sequence (virtual protected member function of std::basic_streambuf<CharT,Traits>)
ebackgptregptr	returns a pointer to the beginning, current character and the end of the get area (protected member function)
gbump	advances the next pointer in the input sequence (protected member function)
setg	repositions the beginning, next, and end pointers of the input sequence (protected member function)
Put area
xsputn [virtual]	writes multiple characters to the output sequence (virtual protected member function of std::basic_streambuf<CharT,Traits>)
overflow [virtual]	writes characters to the associated output sequence from the put area (virtual protected member function of std::basic_streambuf<CharT,Traits>)
pbasepptrepptr	returns a pointer to the beginning, current character and the end of the put area (protected member function)
pbump	advances the next pointer of the output sequence (protected member function)
setp	repositions the beginning, next, and end pointers of the output sequence (protected member function)
Putback
pbackfail [virtual]	puts a character back into the input sequence, possibly modifying the input sequence (virtual protected member function of std::basic_streambuf<CharT,Traits>)

Notes

Feature-test macro	Value	Std	Feature
__cpp_lib_syncbuf	201803L	(C++20)	Synchronized buffered ostream (std::syncbuf, std::osyncstream) and manipulators