Overrides basic_streambuf::setbuf()
virtual basic_streambuf<charT traits>* setbuf (char_type* s, streamsize n);
Setbuf returns zero if the file pointer fp is a null pointer. Otherwise, it calls setvbuf(fp, (char *)buffer, _IOFBF, n * sizeof (E)) to offer the array of n elements beginning at s as a buffer for the stream. If that function returns a nonzero value, the function returns a null pointer. Otherwise, the this pointer is returned to signal success.