The three types of stream buffering available are unbuffered, block buffered,
and line buffered.
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 line buffered, characters are saved up until a newline
is output or input is read from any stream attached to a terminal device
function may be used to force the block out early.
Normally, all files are block buffered.
When the first
operation occurs on a file,
and an optimally sized buffer is obtained.
If a stream refers to a terminal
normally does), it is line buffered.
The standard error stream
is initially unbuffered.
function may be used to alter the buffering behavior of a stream.
parameter must be one of the following three macros:
parameter may be given as zero
to obtain deferred optimal-size buffer allocation as usual.
If it is not zero, then except for unbuffered files, the
argument should point to a buffer at least
this buffer will be used instead of the current buffer.
is not zero but
a buffer of the given size will be allocated immediately,
and released on close.
This is an extension to ANSI C;
portable code should use a size of 0 with any
function may be used at any time,
but may have peculiar side effects
(such as discarding input or flushing output)
if the stream is
Portable applications should call it only once on any given stream,
and before any
The other three calls are, in effect, simply aliases for calls to
Except for the lack of a return value, the
function is exactly equivalent to the call
"setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);"
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, NULL, _IOLBF, 0);"
function returns 0 on success, or
if the request cannot be honored
(note that the stream is still functional in this case).
function returns what the equivalent
would have returned.