<streambuf>
Include the iostreams standard header <streambuf> to define the template class basic_streambuf, which is basic to the operation of the iostreams classes. This header is typically included for you by another of the iostreams headers; you rarely need to include it directly.
For a list of all members of this header, see <streambuf> Members.
#include <streambuf>
See Also
Reference
Thread Safety in the Standard C++ Library