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(): _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 out-
       put 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 follow-
       ing 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 only be used 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  deter-
       mined by the default BUFSIZ.  The setlinebuf() function is exactly equivalent to the call:

           setvbuf(stream, (char *) 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.

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

BUGS
       The setbuffer() and setlinebuf() functions are not portable to versions of BSD before 4.2BSD,  and  are  available  under
       Linux  since  libc  4.5.21.   On  4.2BSD  and 4.3BSD systems, setbuf() always uses a suboptimal buffer size and should be
       avoided.

       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;
       }

SEE ALSO
       fclose(3), fflush(3), fopen(3), fread(3), malloc(3), printf(3), puts(3)

COLOPHON
       This  page  is  part of release 3.25 of the Linux man-pages project.  A description of the project, and information about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2008-06-26                                                  SETBUF(3)