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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | CONFORMING TO | BUGS | SEE ALSO | COLOPHON |
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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():
Since glibc 2.19:
_DEFAULT_SOURCE
Glibc 2.19 and earlier:
_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. 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 be used only
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, 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.
For an explanation of the terms used in this section, see
attributes(7).
┌────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────────────────┼───────────────┼─────────┤
│setbuf(), setbuffer(), │ Thread safety │ MT-Safe │
│setlinebuf(), setvbuf() │ │ │
└────────────────────────┴───────────────┴─────────┘
The setbuf() and setvbuf() functions conform to C89 and C99.
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;
}
stdbuf(1), fclose(3), fflush(3), fopen(3), fread(3), malloc(3),
printf(3), puts(3)
This page is part of release 5.10 of the Linux man-pages project.
A description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2019-03-06 SETBUF(3)
Pages that refer to this page: fclose(3), fcloseall(3), fflush(3), fpurge(3), open_memstream(3), stdin(3), stdio(3)
Copyright and license for this manual page
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