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RedHat 9 (Linux i386) - man page for setvbuf (redhat section 3)

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 termi-
       nal 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 func-
       tion 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 param-
       eter 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 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  call-
       er,  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 termination.

       For example, the following is illegal:

       #include <stdio.h>
       int main()
       {
	   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)

Linux					    2001-06-09					SETBUF(3)


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