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SETBUF(3) Linux Programmer's Manual SETBUF(3)
setbuf, setbuffer, setlinebuf, setvbuf - stream buffering operations
#include <stdio.h>
void setbuf(FILE *stream, char *buf);
void setbuffer(FILE *stream, char *buf, size_t size);
void setlinebuf(FILE *stream);
int setvbuf(FILE *stream, char *buf, int mode, size_t size);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
setbuffer(), setlinebuf(): _BSD_SOURCE
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 newline 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 by default.
The setvbuf() function may be used on any open stream to change its buffer.
The mode argument 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
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 setvbuf().
The setbuf() function is exactly equivalent to the call
setvbuf(stream, buf, buf ? _IOFBF : _IONBF, 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);
The function setvbuf() returns 0 on success. It returns nonzero on failure
(mode is invalid or the request cannot be honored). It may set errno on
failure.
The other functions do not return a value.
The setbuf() and setvbuf() functions conform to C89 and C99.
The setbuffer() and setlinebuf() 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, setbuf() always uses a suboptimal buffer size and should be
avoided.
You must make sure that the space that buf points to still exists by the time
stream is closed, which also happens at program termination. For example, the
following is invalid:
#include <stdio.h>
int
main(void)
{
char buf[BUFSIZ];
setbuf(stdin, buf);
printf("Hello, world!\n");
return 0;
}
fclose(3), fflush(3), fopen(3), fread(3), malloc(3), printf(3), puts(3)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2008-06-26 SETBUF(3)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface