The three types of buffering available are unbuffered, block buffered, and
When an output stream is unbuffered, information appears on
the destination file or terminal as soon as written; when it is block
buffered many characters are saved up and written as a block; when it is
line buffered characters are saved up until a newline is output or input is
read from any stream attached to a terminal device (typically stdin).
may be used to force the block out early.
Normally all files are block buffered.
When the first I/O operation occurs on a file,
is called, and a buffer is obtained.
If a stream refers to a terminal (as
normally does) it is line buffered.
The standard error stream
is always unbuffered by default.
function may be used on any open stream to change its buffer.
argument must be one of the following three macros:
Except for unbuffered files, the
argument should point to a buffer at least
bytes long; this buffer will be used instead of the current buffer.
If the argument
only the mode is affected; a new buffer will be allocated on the next read
or write operation.
function may only be used after opening a stream and before any other
operations have been performed on it.
The other three calls are, in effect, simply aliases for calls to
function is exactly equivalent to the call
function is the same, except that the size of the buffer is up to the
caller, rather than being determined by the default
function is exactly equivalent to the call:
setvbuf(stream, (char *) NULL, _IOLBF, 0);
returns 0 on success.
It returns non-zero on failure
is invalid or the request cannot be honored).
It may set
The other functions do not return a value.
functions conform to C89 and C99.
functions are not portable to versions of BSD before 4.2BSD, and
are available under Linux since libc 4.5.21.
On 4.2BSD and 4.3BSD systems,
always uses a suboptimal buffer size and should be avoided.
You must make sure that the space that
points to still exists by the time
is closed, which also happens at program termination.
For example, the following is invalid: