std::basic_streambuf

 

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basic_streambuf

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std::basic_streambuf

Public member functions basic_streambuf::~basic_streambuf      Locales basic_streambuf::pubimbue basic_streambuf::getloc Positioning basic_streambuf::pubsetbuf basic_streambuf::pubseekoff basic_streambuf::pubseekpos basic_streambuf::pubsync Get area basic_streambuf::in_avail basic_streambuf::snextc basic_streambuf::sbumpc basic_streambuf::sgetc basic_streambuf::sgetn Put area basic_streambuf::sputc basic_streambuf::sputn Putback basic_streambuf::sputbackc basic_streambuf::sungetc

Protected member functions basic_streambuf::basic_streambuf basic_streambuf::operator= (C++11) basic_streambuf::swap (C++11) Locales basic_streambuf::imbue Positioning basic_streambuf::setbuf basic_streambuf::seekoff basic_streambuf::seekpos basic_streambuf::sync Get area basic_streambuf::showmanyc basic_streambuf::underflow basic_streambuf::uflow basic_streambuf::xsgetn basic_streambuf::ebackbasic_streambuf::gptrbasic_streambuf::egptr basic_streambuf::gbump basic_streambuf::setg Put area basic_streambuf::xsputn basic_streambuf::overflow basic_streambuf::pbasebasic_streambuf::pptrbasic_streambuf::epptr basic_streambuf::pbump basic_streambuf::setp Putback basic_streambuf::pbackfail

 

Defined in header <streambuf>
template<     class CharT,     class Traits = std::char_traits<CharT> > class basic_streambuf;

The class basic_streambuf controls input and output to a character sequence. It includes and provides access to

1. The controlled character sequence, also called the buffer, which may contain input sequence (also called get area) for buffering the input operations and/or output sequence (also called put area) for buffering the output operations.
2. The associated character sequence, also called source (for input) or sink (for output). This may be an entity that is accessed through OS API (file, TCP socket, serial port, other character device), or it may be an object (std::vector, array, string literal), that can be interpreted as a character source or sink.

The I/O stream objects std::basic_istream and std::basic_ostream, as well as all objects derived from them (std::ofstream, std::stringstream, etc), are implemented entirely in terms of std::basic_streambuf.

The controlled character sequence is an array of CharT which, at all times, represents a subsequence, or a "window" into the associated character sequence. Its state is described by three pointers:

1. The beginning pointer, always points at the lowest element of the buffer.
2. The next pointer, points at the element that is the next candidate for reading or writing.
3. The end pointer, points one past the end of the buffer.

A basic_streambuf object may support input (in which case the buffer described by the beginning, next, and end pointers is called get area), output (put area), or input and output simultaneously. In latter case, six pointers are tracked, which may all point to elements of the same character array or two individual arrays.

If the next pointer is less than the end pointer in the put area, a write position is available. The next pointer can be dereferenced and assigned to.

If the next pointer is less than the end pointer in the get area, a read position is available. The next pointer can be dereferenced and read from.

If the next pointer is greater than the beginning pointer in a get area, a putback position is available, and the next pointer may be decremented, dereferenced, and assigned to, in order to put a character back into the get area.

The character representation and encoding in the controlled sequence may be different from the character representations in the associated sequence, in which case a std::codecvt locale facet is typically used to perform the conversion. Common examples are UTF-8 (or other multibyte) files accessed through std::wfstream objects: the controlled sequence consists of wchar_t characters, but the associated sequence consists of bytes.

Typical implementation of the std::basic_streambuf base class holds only the six CharT* pointers and a copy of std::locale as data members. In addition, implementations may keep cached copies of locale facets, which are invalidated whenever imbue() is called. The concrete buffers such as std::basic_filebuf or std::basic_stringbuf are derived from std::basic_streambuf.

Several typedefs for common character types are provided:

Defined in header <streambuf>
Type	Definition
std::streambuf	std::basic_streambuf<char>
std::wstreambuf	std::basic_streambuf<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

Member functions

(destructor) [virtual]	destructs the basic_streambuf object (virtual public member function)
Locales
pubimbue	invokes imbue() (public member function)
getloc	obtains a copy of the associated locale (public member function)
Positioning
pubsetbuf	invokes setbuf() (public member function)
pubseekoff	invokes seekoff() (public member function)
pubseekpos	invokes seekpos() (public member function)
pubsync	invokes sync() (public member function)
Get area
in_avail	obtains the number of characters immediately available in the get area (public member function)
snextc	advances the input sequence, then reads one character without advancing again (public member function)
sbumpcstossc (removed in C++17)	reads one character from the input sequence and advances the sequence (public member function)
sgetc	reads one character from the input sequence without advancing the sequence (public member function)
sgetn	invokes xsgetn() (public member function)
Put area
sputc	writes one character to the put area and advances the next pointer (public member function)
sputn	invokes xsputn() (public member function)
Putback
sputbackc	puts one character back in the input sequence (public member function)
sungetc	moves the next pointer in the input sequence back by one (public member function)
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)
Positioning
setbuf [virtual]	replaces the buffer with user-defined array, if permitted (virtual protected member function)
seekoff [virtual]	repositions the next pointer in the input sequence, output sequence, or both, using relative addressing (virtual protected member function)
seekpos [virtual]	repositions the next pointer in the input sequence, output sequence, or both using absolute addressing (virtual protected member function)
sync [virtual]	synchronizes the buffers with the associated character sequence (virtual protected member function)
Get area
showmanyc [virtual]	obtains the number of characters available for input in the associated input sequence, if known (virtual protected member function)
underflow [virtual]	reads characters from the associated input sequence to the get area (virtual protected member function)
uflow [virtual]	reads characters from the associated input sequence to the get area and advances the next pointer (virtual protected member function)
xsgetn [virtual]	reads multiple characters from the input sequence (virtual protected member function)
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)
overflow [virtual]	writes characters to the associated output sequence from the put area (virtual protected member function)
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)

See also

FILE	object type, capable of holding all information needed to control a C I/O stream (typedef)