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
   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

   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!\n");
       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 4.09 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/.

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