<TITLE>setbuf</TITLE>
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<h3>SETBUF(3) Linux Programmer's Manual SETBUF(3)
</h3>
<h3>NAME
</h3> setbuf, setbuffer, setlinebuf, setvbuf - stream buffering
operations
<h3>SYNOPSIS
</h3> #include <stdio.h>
int setbuf( FILE *stream, char *buf);
int setbuffer( FILE *stream, char *buf, size_tsize);
int setlinebuf( FILE *stream);
int setvbuf( FILE *stream, char *buf, int mode , size_t
size);
<h3>DESCRIPTION
</h3> The three types of 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
it is line buffered characters are saved up until a new-
line is output or input is read from any stream attached
to a terminal device (typically stdin). The function
fflush(3) may be used to force the block out early. (See
fclose(3).) Normally all files are block buffered. When
the first I/O operation occurs on a file, malloc(3) is
called, and a buffer is obtained. If a stream refers to a
terminal (as stdout normally does) it is line buffered.
The standard error stream stderr is always unbuffered.
The setvbuf function may be used at any time on any open
stream to change its buffer. The mode parameter must be
one of the following three macros:
_IONBF unbuffered
_IOLBF line buffered
_IOFBF fully buffered
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 argument buf
is NULL, only the mode is affected; a new buffer will be
allocated on the next read or write operation. The
setvbuf function may be used at any time, but can only
change the mode of a stream when it is not ``active'':
that is, before any I/O, or immediately after a call to
fflush.
The other three calls are, in effect, simply aliases for
calls to setvbuf. The setbuf function is exactly equiva-
lent to the call
setvbuf(stream, buf, buf _IOFBF : _IONBF,
<h3>BSD MANPAGE 29 November 1993 1
</h3>
<h3>SETBUF(3) Linux Programmer's Manual SETBUF(3)
</h3>
BUFSIZ);
The setbuffer function is the same, except that the size
of the buffer is up to the caller, rather than being
determined by the default BUFSIZ. The setlinebuf function
is exactly equivalent to the call:
setvbuf(stream, (char *)NULL, _IOLBF, 0);
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<h3>SEE ALSO
</h3><p>
<a href=fopen.htm>fopen</a>,
<a href=fclose.htm>fclose</a>,
<a href=fread.htm>fread</a>,
<a href=malloc.htm>malloc</a>,
<a href=puts.htm>puts</a>,
<a href=printf.htm>printf</a>,
<pre>
<h3>STANDARDS
</h3> The setbuf and setvbuf functions conform to ANSI
C3.159-1989 (``ANSI C'').
<h3>BUGS
</h3> The setbuffer and setlinebuf functions are not portable to
versions of BSD before 4.2BSD, and may not be available
under Linux. On 4.2BSD and 4.3BSD systems, setbuf always
uses a suboptimal buffer size and should be avoided.
You must make sure that both buf and the space it points
to still exist by the time stream is closed, which also
happens at program termination.
For example, the following is illegal:
#include <stdio.h>
int main()
{
char buf[BUFSIZ];
setbuf(stdin, buf);
printf("Hello, world!\n");
return 0;
}
<h3>BSD MANPAGE 29 November 1993 2
</h3>
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