setbuf(3) - Linux manual page (original) (raw)
setbuf(3) Library Functions Manual setbuf(3)
NAME top
setbuf, setbuffer, setlinebuf, setvbuf - stream buffering
operationsLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <stdio.h>**
**int setvbuf(FILE *restrict** _stream_**, char** _buf_**[restrict .**_size_**],**
**int** _mode_**, size_t** _size_**);**
**void setbuf(FILE *restrict** _stream_**, char *restrict** _buf_**);**
**void setbuffer(FILE *restrict** _stream_**, char** _buf_**[restrict .**_size_**],**
**size_t** _size_**);**
**void setlinebuf(FILE ***_stream_**);**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_SOURCEDESCRIPTION top
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)](../man3/fflush.3.html) may be used to force the block out early. (See
[fclose(3)](../man3/fclose.3.html).)
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);RETURN VALUE top
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](../man3/errno.3.html)_ on failure.
The other functions do not return a value.ATTRIBUTES top
For an explanation of the terms used in this section, see
[attributes(7)](../man7/attributes.7.html).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ **Interface** │ **Attribute** │ **Value** │
├──────────────────────────────────────┼───────────────┼─────────┤
│ **setbuf**(), **setbuffer**(), **setlinebuf**(), │ Thread safety │ MT-Safe │
│ **setvbuf**() │ │ │
└──────────────────────────────────────┴───────────────┴─────────┘STANDARDS top
**setbuf**()
**setvbuf**()
C11, POSIX.1-2008.HISTORY top
**setbuf**()
**setvbuf**()
C89, POSIX.1-2001.CAVEATS top
POSIX notes that the value of _[errno](../man3/errno.3.html)_ is unspecified after a call to
**setbuf**() and further notes that, since the value of _[errno](../man3/errno.3.html)_ is not
required to be unchanged after a successful call to **setbuf**(),
applications should instead use **setvbuf**() in order to detect
errors.BUGS top
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(stdout, buf);
printf("Hello, world!\n");
return 0;
}SEE ALSO top
[stdbuf(1)](../man1/stdbuf.1.html), [fclose(3)](../man3/fclose.3.html), [fflush(3)](../man3/fflush.3.html), [fopen(3)](../man3/fopen.3.html), [fread(3)](../man3/fread.3.html), [malloc(3)](../man3/malloc.3.html),
[printf(3)](../man3/printf.3.html), [puts(3)](../man3/puts.3.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 setbuf(3)
Pages that refer to this page:fclose(3), fcloseall(3), fflush(3), fpurge(3), open_memstream(3), procio(3), stdin(3), stdio(3)