Sets the buffering mode for an output file.
There are three available modes:
no buffering; the result of any output operation appears immediately.
full buffering; output operation is performed only
when the buffer is full (or when you explicitly
flush the file
line buffering; output is buffered until a newline is output
or there is any input from some special files
(such as a terminal device).
For the last two cases,
specifies the size of the buffer, in bytes.
The default is an appropriate size.