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.\" @(#)setbuf.3 6.10 (Berkeley) 6/29/91
.Nd stream buffering operations
.Fn setbuf "FILE *stream" "char *buf"
.Fn setbuffer "FILE *stream" "char *buf" "size_t size"
.Fn setlinebuf "FILE *stream"
.Fn setvbuf "FILE *stream" "char *buf" "int mode" "size_t size"
The three types of buffering available are unbuffered, block 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 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
may be used to force the block out early.
Normally all files are block buffered.
operation occurs on a file,
and a buffer is obtained.
If a stream refers to a terminal
normally does) it is line buffered.
The standard error stream
may be used at any time on any open stream
parameter must be one of the following three macros:
.Bl -tag -width _IOFBF -offset indent
Except for unbuffered files, the
argument should point to a buffer at least
this buffer will be used instead of the current buffer.
only the mode is affected;
a new buffer will be allocated on the next read or write operation.
but can only change the mode of a stream
when it is not ``active'':
or immediately after a call to
The other three calls are, in effect, simply aliases
is exactly equivalent to the call
.Dl setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);
is the same, except that the size of the buffer is up to the caller,
rather than being determined by the default
is exactly equivalent to the call:
.Dl setvbuf(stream, (char *)NULL, _IOLBF, 0);
functions are not portable to versions of
always uses a suboptimal buffer size and should be avoided.