30 Input/output library [input.output]

30.6 Stream buffers [stream.buffers]

30.6.1 Header <streambuf> synopsis [streambuf.syn]

namespace std {
  template<class charT, class traits = char_traits<charT>>
    class basic_streambuf;
  using streambuf  = basic_streambuf<char>;
  using wstreambuf = basic_streambuf<wchar_t>;
}
The header <streambuf> defines types that control input from and output to character sequences.