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std::basic_osyncstream

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Defined in header <syncstream>
template<

    class CharT,
    class Traits = std::char_traits <CharT>,
    class Allocator = std::allocator <CharT>

> class basic_osyncstream : public std::basic_ostream <CharT, Traits>
(since C++20)

The class template std::basic_osyncstream is a convenience wrapper for std::basic_syncbuf. It provides a mechanism to synchronize threads writing to the same stream.

It can be used with a named variable: 

{
 std::osyncstream synced_out(std::cout ); // synchronized wrapper for std::cout
 synced_out << "Hello, ";
 synced_out << "World!";
 synced_out << std::endl ; // flush is noted, but not yet performed
 synced_out << "and more!\n";
} // characters are transferred and std::cout is flushed

as well as with a temporary: 

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

It provides the guarantee that all output made to the same final destination buffer (std::cout in the examples above) will be free of data races and will not be interleaved or garbled in any way, as long as every write to that final destination buffer is made through (possibly different) instances of std::basic_osyncstream.

Typical implementation of std::basic_osyncstream holds only one member: the wrapped std::basic_syncbuf.

std-basic osyncstream-inheritance.svg

Inheritance diagram

Several typedefs for common character types are provided:

Defined in header <syncstream>
Type Definition
std::osyncstream std::basic_osyncstream<char>
std::wosyncstream std::basic_osyncstream<wchar_t>

Contents

[edit] Member types

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

[edit] Member functions

constructs a basic_osyncstream object
(public member function) [edit]
assigns a basic_osyncstream object
(public member function) [edit]
destroys the basic_osyncstream and emits its internal buffer
(public member function) [edit]
obtains a pointer to the underlying basic_syncbuf
(public member function) [edit]
obtains a pointer to the final destination stream buffer
(public member function) [edit]
calls emit() on the underlying basic_syncbuf to transmit its internal data to the final destination
(public member function) [edit]

Inherited from std::basic_ostream

Member functions

Formatted output
inserts formatted data
(public member function of std::basic_ostream<CharT,Traits>) [edit]
Unformatted output
inserts a character
(public member function of std::basic_ostream<CharT,Traits>) [edit]
inserts blocks of characters
(public member function of std::basic_ostream<CharT,Traits>) [edit]
Positioning
returns the output position indicator
(public member function of std::basic_ostream<CharT,Traits>) [edit]
sets the output position indicator
(public member function of std::basic_ostream<CharT,Traits>) [edit]
Miscellaneous
synchronizes with the underlying storage device
(public member function of std::basic_ostream<CharT,Traits>) [edit]

Member classes

implements basic logic for preparation of the stream for output operations
(public member class of std::basic_ostream<CharT,Traits>) [edit]

Inherited from std::basic_ios

Member types

Member type Definition
char_type CharT
traits_type Traits
int_type Traits::int_type
pos_type Traits::pos_type
off_type Traits::off_type

Member functions

State functions
checks if no error has occurred i.e. I/O operations are available
(public member function of std::basic_ios<CharT,Traits>) [edit]
checks if end-of-file has been reached
(public member function of std::basic_ios<CharT,Traits>) [edit]
checks if an error has occurred
(public member function of std::basic_ios<CharT,Traits>) [edit]
checks if a non-recoverable error has occurred
(public member function of std::basic_ios<CharT,Traits>) [edit]
checks if an error has occurred (synonym of fail() )
(public member function of std::basic_ios<CharT,Traits>) [edit]
checks if no error has occurred (synonym of !fail() )
(public member function of std::basic_ios<CharT,Traits>) [edit]
returns state flags
(public member function of std::basic_ios<CharT,Traits>) [edit]
sets state flags
(public member function of std::basic_ios<CharT,Traits>) [edit]
modifies state flags
(public member function of std::basic_ios<CharT,Traits>) [edit]
Formatting
copies formatting information
(public member function of std::basic_ios<CharT,Traits>) [edit]
manages the fill character
(public member function of std::basic_ios<CharT,Traits>) [edit]
Miscellaneous
manages exception mask
(public member function of std::basic_ios<CharT,Traits>) [edit]
sets the locale
(public member function of std::basic_ios<CharT,Traits>) [edit]
manages associated stream buffer
(public member function of std::basic_ios<CharT,Traits>) [edit]
manages tied stream
(public member function of std::basic_ios<CharT,Traits>) [edit]
narrows characters
(public member function of std::basic_ios<CharT,Traits>) [edit]
widens characters
(public member function of std::basic_ios<CharT,Traits>) [edit]

Inherited from std::ios_base

Member functions

Formatting
manages format flags
(public member function of std::ios_base) [edit]
sets specific format flag
(public member function of std::ios_base) [edit]
clears specific format flag
(public member function of std::ios_base) [edit]
manages decimal precision of floating point operations
(public member function of std::ios_base) [edit]
manages field width
(public member function of std::ios_base) [edit]
Locales
sets locale
(public member function of std::ios_base) [edit]
returns current locale
(public member function of std::ios_base) [edit]
Internal extensible array
[static]
returns a program-wide unique integer that is safe to use as index to pword() and iword()
(public static member function of std::ios_base) [edit]
resizes the private storage if necessary and access to the long element at the given index
(public member function of std::ios_base) [edit]
resizes the private storage if necessary and access to the void* element at the given index
(public member function of std::ios_base) [edit]
Miscellaneous
registers event callback function
(public member function of std::ios_base) [edit]
sets whether C++ and C I/O libraries are interoperable
(public static member function of std::ios_base) [edit]
Member classes
stream exception
(public member class of std::ios_base) [edit]
initializes standard stream objects
(public member class of std::ios_base) [edit]

Member types and constants

Type Explanation
stream open mode type

The following constants are also defined:

Constant Explanation[edit]
app seek to the end of stream before each write[edit]
binary open in binary mode [edit]
in open for reading[edit]
out open for writing[edit]
trunc discard the contents of the stream when opening[edit]
ate seek to the end of stream immediately after open[edit]
noreplace (C++23) open in exclusive mode[edit]

(typedef) [edit] formatting flags type

The following constants are also defined:

Constant Explanation[edit]
dec use decimal base for integer I/O: see std::dec [edit]
oct use octal base for integer I/O: see std::oct [edit]
hex use hexadecimal base for integer I/O: see std::hex [edit]
basefield dec | oct | hex. Useful for masking operations[edit]
left left adjustment (adds fill characters to the right): see std::left [edit]
right right adjustment (adds fill characters to the left): see std::right [edit]
internal internal adjustment (adds fill characters to the internal designated point): see std::internal [edit]
adjustfield left | right | internal. Useful for masking operations[edit]
scientific generate floating point types using scientific notation, or hex notation if combined with fixed: see std::scientific [edit]
fixed generate floating point types using fixed notation, or hex notation if combined with scientific: see std::fixed [edit]
floatfield scientific | fixed. Useful for masking operations[edit]
boolalpha insert and extract bool type in alphanumeric format: see std::boolalpha [edit]
showbase generate a prefix indicating the numeric base for integer output, require the currency indicator in monetary I/O: see std::showbase [edit]
showpoint generate a decimal-point character unconditionally for floating-point number output: see std::showpoint [edit]
showpos generate a + character for non-negative numeric output: see std::showpos [edit]
skipws skip leading whitespace before certain input operations: see std::skipws [edit]
unitbuf flush the output after each output operation: see std::unitbuf [edit]
uppercase replace certain lowercase letters with their uppercase equivalents in certain output operations: see std::uppercase [edit]

(typedef) [edit] state of the stream type

The following constants are also defined:

Constant Explanation[edit]
goodbit no error[edit]
badbit irrecoverable stream error[edit]
failbit input/output operation failed (formatting or extraction error)[edit]
eofbit associated input sequence has reached end-of-file[edit]

(typedef) [edit] seeking direction type

The following constants are also defined:

Constant Explanation[edit]
beg the beginning of a stream[edit]
end the ending of a stream[edit]
cur the current position of stream position indicator[edit]

(typedef) [edit] specifies event type
(enum) [edit] callback function type
(typedef) [edit]

[edit] Notes

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

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