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

NAME

       setbuf, setbuffer, setlinebuf, setvbuf - stream buffering operations

SYNOPSIS

       #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

DESCRIPTION

       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  opera-
       tion.  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

       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

       For an explanation of the terms used in this section, see attributes(7).

       +------------------------+---------------+---------+
       |Interface               | Attribute     | Value   |
       +------------------------+---------------+---------+
       |setbuf(), setbuffer(),  | Thread safety | MT-Safe |
       |setlinebuf(), setvbuf() |               |         |
       +------------------------+---------------+---------+
CONFORMING TO

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

BUGS

       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!
");
           return 0;
       }

SEE ALSO

       stdbuf(1), fclose(3), fflush(3), fopen(3), fread(3), malloc(3), printf(3), puts(3)

COLOPHON

       This page is part of release 4.15 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                                                               2017-09-15                                                           SETBUF(3)