std::basic_syncbuf (3) - Linux Manuals

std::basic_syncbuf: std::basic_syncbuf

NAME

std::basic_syncbuf - std::basic_syncbuf

Synopsis

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

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 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.
Two specializations for common character types are also defined:

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

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

Protected member functions

                 either emits, or records a pending flush, depending on the current emit-on-sync policy
sync (public member function)

Non-member functions

std::swap(std::basic_syncbuf) specializes the std::swap algorithm
                              (function template)
(C++20)

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 destructs the basic_streambuf object
                      (virtual public member function of std::basic_streambuf<CharT,Traits>)
[virtual]

Locales

                      invokes imbue()
pubimbue (public member function of std::basic_streambuf<CharT,Traits>)
                      obtains a copy of the associated locale
getloc (public member function of std::basic_streambuf<CharT,Traits>)

Positioning

                      invokes setbuf()
pubsetbuf (public member function of std::basic_streambuf<CharT,Traits>)
                      invokes seekoff()
pubseekoff (public member function of std::basic_streambuf<CharT,Traits>)
                      invokes seekpos()
pubseekpos (public member function of std::basic_streambuf<CharT,Traits>)
                      invokes sync()
pubsync (public member function of std::basic_streambuf<CharT,Traits>)

Get area

                      obtains the number of characters immediately available in the get area
in_avail (public member function of std::basic_streambuf<CharT,Traits>)
                      advances the input sequence, then reads one character without advancing again
snextc (public member function of std::basic_streambuf<CharT,Traits>)
                      reads one character from the input sequence and advances the sequence
sbumpc (public member function of std::basic_streambuf<CharT,Traits>)

stossc advances the input sequence as if by calling sbumpc() and discarding the result
                      (public member function)
(deprecated in C++98)
(removed in C++17)
                      reads one character from the input sequence without advancing the sequence
sgetc (public member function of std::basic_streambuf<CharT,Traits>)
                      invokes xsgetn()
sgetn (public member function of std::basic_streambuf<CharT,Traits>)

Put area

                      writes one character to the put area and advances the next pointer
sputc (public member function of std::basic_streambuf<CharT,Traits>)
                      invokes xsputn()
sputn (public member function of std::basic_streambuf<CharT,Traits>)

Putback

                      puts one character back in the input sequence
sputbackc (public member function of std::basic_streambuf<CharT,Traits>)
                      moves the next pointer in the input sequence back by one
sungetc (public member function of std::basic_streambuf<CharT,Traits>)

Protected member functions

              constructs a basic_streambuf object
constructor (protected member function)

operator= replaces a basic_streambuf object
              (protected member function)
(C++11)

swap swaps two basic_streambuf objects
              (protected member function)
(C++11)

Locales

imbue changes the associated locale
              (virtual protected member function of std::basic_streambuf<CharT,Traits>)
[virtual]

Positioning

setbuf replaces the buffer with user-defined array, if permitted
              (virtual protected member function of std::basic_streambuf<CharT,Traits>)
[virtual]

seekoff 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>)
[virtual]

seekpos 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>)
[virtual]

sync synchronizes the buffers with the associated character sequence
              (virtual protected member function of std::basic_streambuf<CharT,Traits>)
[virtual]

Get area

showmanyc 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>)
[virtual]

underflow reads characters from the associated input sequence to the get area
              (virtual protected member function of std::basic_streambuf<CharT,Traits>)
[virtual]

uflow 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>)
[virtual]

xsgetn reads multiple characters from the input sequence
              (virtual protected member function of std::basic_streambuf<CharT,Traits>)
[virtual]

eback returns a pointer to the beginning, current character and the end of the get area
gptr (protected member function)
egptr
              advances the next pointer in the input sequence
gbump (protected member function)
              repositions the beginning, next, and end pointers of the input sequence
setg (protected member function)

Put area

xsputn writes multiple characters to the output sequence
              (virtual protected member function of std::basic_streambuf<CharT,Traits>)
[virtual]

overflow writes characters to the associated output sequence from the put area
              (virtual protected member function of std::basic_streambuf<CharT,Traits>)
[virtual]

pbase returns a pointer to the beginning, current character and the end of the put area
pptr (protected member function)
epptr
              advances the next pointer of the output sequence
pbump (protected member function)
              repositions the beginning, next, and end pointers of the output sequence
setp (protected member function)

Putback

pbackfail puts a character back into the input sequence, possibly modifying the input sequence
              (virtual protected member function of std::basic_streambuf<CharT,Traits>)
[virtual]