Section: Linux Programmer's Manual (3)
setbuf, setbuffer, setlinebuf, setvbuf - stream buffering operations
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
Since glibc 2.19:
Glibc 2.19 and earlier:
The three types of buffering available are unbuffered, block buffered, and
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
may be used to force the block out early.
Normally all files are block buffered.
If a stream refers to a terminal (as
normally does), it is line buffered.
The standard error stream
is always unbuffered by default.
function may be used on any open stream to change its buffer.
argument must be one of the following three macros:
Except for unbuffered files, the
argument should point to a buffer at least
bytes long; this buffer will be used instead of the current buffer.
If the argument
only the mode is affected; a new buffer will be allocated on the next read
or write operation.
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
function is exactly equivalent to the call
setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);
function is the same, except that the size of the buffer is up to the
caller, rather than being determined by the default
function is exactly equivalent to the call:
setvbuf(stream, NULL, _IOLBF, 0);
returns 0 on success.
It returns nonzero on failure
is invalid or the request cannot be honored).
It may set
The other functions do not return a value.
For an explanation of the terms used in this section, see
functions conform to C89 and C99.
You must make sure that the space that
points to still exists by the time
is closed, which also happens at program termination.
For example, the following is invalid:
This page is part of release 5.10 of the Linux
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at