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       setbuf, setbuffer, setlinebuf, setvbuf - stream buffering operations


       #include <stdio.h>

       void setbuf(FILE *stream, char *buf);
       void setbuffer(FILE *stream, char *buf, size_tsize);
       void setlinebuf(FILE *stream);
       int setvbuf(FILE *stream, char *buf, int mode , size_t size);


       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 at any time on any open stream to change its buffer.  The
       mode parameter 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 at any time, but can only change the mode  of
       a  stream  when it is not ``active'': that is, before any I/O, or immediately after a call
       to fflush.

       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, (char *)NULL, _IOLBF, 0);


       The setbuf and setvbuf functions conform to ANSI X3.159-1989 (``ANSI C'').


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

       You must make sure that both buf and the space it points to still exist by the time stream
       is closed, which also happens at program termination.

       For example, the following is illegal:

       #include <stdio.h>
       int main()
           char buf[BUFSIZ];
           setbuf(stdin, buf);
           printf("Hello, world!\n");
           return 0;


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