Set buffer.
  This member is called to set a new buffer for the streambuf-derived object. Its default behavior for this class is just to return this.
  This is a virtual member function that should be redefined in derived classes to behave as expected setting the array of n characters pointed by s as the new character buffer.
  Standard class filebuf redefines this specifically for filebuf objects (filebuf::setbuf).

Parameters.

s

Pointer to an array of n characters already allocated in memory. If this parameter is NULL the stream shall be unbuffered.

n

Length in characters of the buffer pointed by s.
This is an integer value of type streamsize

Return Value.
  In case of success the member function should return this, otherwise a null pointer.

Basic template member declaration ( basic_streambuf<charT,traits> ):

typedef charT char_type; basic_streambuf* setbuf ( char_type* s, streamsize n );

See also.
  pubsetbuf, filebuf::setbuf
  streambuf class