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 (), setlinebuf (), setvbuf () |
Thread safety |
MT-Safe |
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)