Write some characters.
  Writes n characters from the array specified by parameter s to the output sequence of the stream buffer.
  This is a virtual member function that can be overridden in derived classes.

Parameters.

s

Pointer to the sequence of characters to be output.

n

Number of character to be put. This is an object of type streamsize.

Return Value.
  The number of characters written.

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

typedef charT char_type; streamsize xsputn (char_type * s, streamsize n);

See also.
  sputn
  streambuf class