streambufs

Streambufs, short for stream buffers, are the foundational components of the C++ iostreams library. A stream buffer (std::streambuf) provides the actual character storage and the interface through which input and output streams access that storage. It sits between higher-level stream objects (std::istream, std::ostream, and their typedefs) and the underlying data sources or destinations, such as files, memory blocks, or strings, enabling buffering, reading, and writing to be performed efficiently and abstractly.

A streambuf maintains separate regions for input (get area) and output (put area). Typical protected members include pointers for the get area: gbase, gptr, and egptr, and pointers for the put area: pbase, pptr, and epptr. The get pointers define the available input characters, while the put pointers define the space allocated for buffered output. The class provides a small set of virtual functions that derived classes override to implement specific behavior, notably underflow/uflow for input and overflow for output, which handle refilling and flushing the buffer. Additional virtuals include sync, seekoff, and seekpos to coordinate with the underlying device, plus xsgetn and xsputn for bulk operations. Public helpers such as pubsetbuf and setg/setp allow configuring the buffers and initial pointers.

Concrete stream buffers include std::filebuf (and std::basic_filebuf) for file I/O, and std::basic_stringbuf (often accessed via std::stringstream or std::stringbuf) for string-based I/O. Users typically interact with streams rather than buffers directly, but custom stream buffers can be derived to adapt streams to devices, network protocols, or special memory layouts by overriding the relevant virtual functions and providing or managing a buffer.

In summary, streambufs encapsulate the buffering and character sequencing logic that underpins the C++ iostreams framework, enabling flexible, efficient, and extensible input and output.