stream buffering operations
*stream, char *buf,
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
\n’) is output or input is read from
any stream attached to a terminal device (typically
The fflush(3) function 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, malloc(3) is called, and an optimally sized buffer is obtained. If a stream refers to a terminal (as stdout normally does), it is line buffered.
The standard error stream stderr is initially unbuffered.
function may be used to alter the buffering behavior of a stream. The
mode parameter must be one of the following three
The size 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 buf argument
should point to a buffer at least size bytes long;
this buffer will be used instead of the current buffer. (If the
size argument is not zero but
NULL, 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
“active”. Portable applications should call it only once on
any given stream, and before any I/O is performed.
Upon successful completion, a value of 0 is returned. If mode is invalid or if the request cannot be honored, a non-zero value is returned, possibly setting errno to indicate the error. The stream is not modified in the error case.
setvbuf() function will fail if:
- The stream specified is not associated with a valid file descriptor.
fclose(3), fopen(3), fread(3), malloc(3), printf(3), puts(3), setbuf(3)
setvbuf() function conforms to
setvbuf() function first appeared in
AT&T System V Release 2 UNIX and
was reimplemented for 4.3BSD-Net/2.