std::basic_streambuf (3) - Linux Man Pages
std::basic_streambuf - std::basic_streambuf
Defined in header <streambuf>
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.
Two convenience typedefs are provided by the standard library
Defined in header <streambuf>
Member type Definition
traits_type Traits; the program is ill-formed if Traits::char_type is not CharT.
destructor destructs the basic_streambuf object
pubimbue (public member function)
getloc (public member function)
pubsetbuf (public member function)
pubseekoff (public member function)
pubseekpos (public member function)
pubsync (public member function)
in_avail (public member function)
snextc (public member function)
sbumpc (public member function)
stossc advances the input sequence as if by calling sbumpc() and discarding the result
(deprecated in C++98)
(removed in C++17)
sgetc (public member function)
sgetn (public member function)
sputc (public member function)
sputn (public member function)
sputbackc (public member function)
sungetc (public member function)
Protected member functions
constructor (protected member function)
operator= replaces a basic_streambuf object
swap swaps two basic_streambuf objects
imbue changes the associated locale
setbuf replaces the buffer with user-defined array, if permitted
seekoff repositions the next pointer in the input sequence, output sequence, or both, using relative addressing
seekpos repositions the next pointer in the input sequence, output sequence, or both using absolute addressing
sync synchronizes the buffers with the associated character sequence
showmanyc obtains the number of characters available for input in the associated input sequence, if known
underflow reads characters from the associated input sequence to the get area
uflow reads characters from the associated input sequence to the get area and advances the next pointer
xsgetn reads multiple characters from the input sequence
eback returns a pointer to the beginning, current character and the end of the get area
gptr (protected member function)
gbump (protected member function)
setg (protected member function)
xsputn writes multiple characters to the output sequence
overflow writes characters to the associated output sequence from the put area
pbase returns a pointer to the beginning, current character and the end of the put area
pptr (protected member function)
pbump (protected member function)
setp (protected member function)
pbackfail puts a character back into the input sequence, possibly modifying the input sequence