Set buffer.
  Sets the array of n characters pointed by s as the new character buffer.

Parameters.

s

Pointer to an array of n characters already allocated in memory. If this parameter is NULL the stream is 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 returns this, otherwise a null pointer.

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

typedef charT char_type; basic_filebuf<charT,traits> * setbuf ( char_type* s, streamsize n );

See also.
  streambuf::pubsetbuf
  filebuf class