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SETBUF(3S)							    SETBUF(3S)

NAME
       setbuf, setvbuf, setbuffer, setlinebuf - assign buffering to a stream

SYNOPSIS
       #include <stdio.h>

       void setbuf(FILE *stream, char *buf);

       void setvbuf(FILE *stream, char *buf, int mode, size_t size);

       setbuffer(stream, buf, size)
       FILE *stream;
       char *buf;
       int size;

       setlinebuf(stream)
       FILE *stream;

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
       encountered or input is read from stdin.	 Fflush (see  fclose(3S))  may
       be  used	 to  force  the block out early.  Normally all files are block
       buffered.  A buffer is obtained from malloc(3) upon the first  getc  or
       putc(3S)	 on  the  file.	  If  the  standard  stream stdout refers to a
       terminal it is line buffered.  The standard  stream  stderr  is	always
       unbuffered.

       Setbuf  is used after a stream has been opened but before it is read or
       written.	 The character array buf is used instead of  an	 automatically
       allocated  buffer.   If	buf is the constant pointer NULL, input/output
       will be completely unbuffered.  A manifest constant  BUFSIZ  tells  how
       big an array is needed:

	      char buf[BUFSIZ];

       Setvbuf,	 an  alternate form of setbuf, is used after a stream has been
       opened but before it is read or written.	 The argument mode  determines
       how the stream will be buffered: _IOFBF causes input/output to be fully
       buffered; _IOLBF causes output  to  be  line  buffered;	_IONBF	causes
       input/output  to	 be  unbuffered.   If  buf  is not a null pointer, the
       character array buf whose size is determined by the  size  argument  is
       used  as the buffer.  If buf is the constant pointer NULL, if required,
       a buffer will be automatically allocated.

       Setbuffer, which is obsoleted by the ANSI C function Setvbuf,  is  used
       after  a	 stream has been opened but before it is read or written.  The
       character array buf whose size is determined by the  size  argument  is
       used  instead  of  an  automatically  allocated	buffer.	 If buf is the
       constant pointer NULL, input/output will be completely unbuffered.

       Setlinebuf, which is obsoleted by the ANSI C function Setvbuf, is  used
       to  change  stdout  or stderr from block buffered or unbuffered to line
       buffered.  Unlike setbuf and setbuffer it can be used at any time  that
       the file descriptor is active.

       A  file	can  be	 changed  from	unbuffered  or	line buffered to block
       buffered by using freopen (see fopen(3S)).  A file can be changed  from
       block buffered or line buffered to unbuffered by using freopen followed
       by setbuf with a buffer argument of NULL.

SEE ALSO
       fopen(3S),  getc(3S),  putc(3S),	  malloc(3),   fclose(3S),   puts(3S),
       printf(3S), fread(3S)

BUGS
       The standard error stream should be line buffered by default.

       The  setbuffer  and setlinebuf functions are not portable to non-4.2BSD
       versions of UNIX.  On 4.2BSD and 4.3BSD systems, setbuf always  uses  a
       suboptimal buffer size and should be avoided.  Setbuffer is not usually
       needed as the default file I/O buffer sizes are optimal.

				 May 12, 1986			    SETBUF(3S)
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