SETBUF(3)                 Linux Programmer's Manual                SETBUF(3)

NAME         top

       setbuf, setbuffer, setlinebuf, setvbuf - stream buffering operations

SYNOPSIS         top

       #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

DESCRIPTION         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) 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 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 on failure.

       The other functions do not return a value.

ATTRIBUTES         top

   Multithreading (see pthreads(7))
       The setbuf(), setbuffer(), setlinebuf(), and setvbuf() functions are

CONFORMING TO         top

       The setbuf() and setvbuf() functions conform to C89 and C99.

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>

           char buf[BUFSIZ];
           setbuf(stdin, buf);
           printf("Hello, world!\n");
           return 0;

SEE ALSO         top

       fclose(3), fflush(3), fopen(3), fread(3), malloc(3), printf(3),

COLOPHON         top

       This page is part of release 3.71 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

Linux                            2014-08-19                        SETBUF(3)