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

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.   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 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 opera-
       tion.  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  determined  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 can return any value on failure, but returns nonzero when mode is invalid or the request
       cannot be honoured. It may set errno on failure.  The other functions are void.

CONFORMING TO

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

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 both buf and the space it points to still exist by the time stream is closed, which also happens at program termi-
       nation.

       For example, the following is illegal:

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

SEE ALSO

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

Linux								    2001-06-09								 SETBUF(3)