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

1. Thecontrolled character sequence, also called thebuffer, which may containinput sequence (also calledget area) for buffering the input operations and/oroutput sequence (also calledput area) for buffering the output operations.
2. Theassociated character sequence, also calledsource (for input) orsink (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 objectsstd::basic_istream andstd::basic_ostream, as well as all objects derived from them (std::ofstream,std::stringstream, etc), are implemented entirely in terms ofstd::basic_streambuf.

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

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

Abasic_streambuf object may support input (in which case the buffer described by the beginning, next, and end pointers is calledget 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, awrite 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, aread 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, aputback 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 astd::codecvt locale facet is typically used to perform the conversion. Common examples are UTF-8 (or other multibyte) files accessed throughstd::wfstream objects: the controlled sequence consists ofwchar_t characters, but the associated sequence consists of bytes.

Typical implementation of thestd::basic_streambuf base class holds only the sixCharT* pointers and a copy ofstd::locale as data members. In addition, implementations may keep cached copies of locale facets, which are invalidated wheneverimbue() is called. The concrete buffers such asstd::basic_filebuf orstd::basic_stringbuf are derived fromstd::basic_streambuf.

Several typedefs for common character types are provided:

[edit]Member types

[edit]Member functions

[edit]See also

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