1.\" Copyright (c) 1980, 1991 Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" the American National Standards Committee X3, on Information 6.\" Processing Systems. 7.\" 8.\" Redistribution and use in source and binary forms, with or without 9.\" modification, are permitted provided that the following conditions 10.\" are met: 11.\" 1. Redistributions of source code must retain the above copyright 12.\" notice, this list of conditions and the following disclaimer. 13.\" 2. Redistributions in binary form must reproduce the above copyright 14.\" notice, this list of conditions and the following disclaimer in the 15.\" documentation and/or other materials provided with the distribution. 16.\" 3. All advertising materials mentioning features or use of this software 17.\" must display the following acknowledgement: 18.\" This product includes software developed by the University of 19.\" California, Berkeley and its contributors. 20.\" 4. Neither the name of the University nor the names of its contributors 21.\" may be used to endorse or promote products derived from this software 22.\" without specific prior written permission. 23.\" 24.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 25.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 26.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 27.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 28.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 29.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 30.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 31.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 32.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 33.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 34.\" SUCH DAMAGE. 35.\" 36.\" from: @(#)setbuf.3 6.10 (Berkeley) 6/29/91 37.\" $Id: setbuf.3,v 1.2 1993/08/01 07:44:51 mycroft Exp $ 38.\" 39.Dd June 29, 1991 40.Dt SETBUF 3 41.Os BSD 4 42.Sh NAME 43.Nm setbuf , 44.Nm setbuffer , 45.Nm setlinebuf , 46.Nm setvbuf 47.Nd stream buffering operations 48.Sh SYNOPSIS 49.Fd #include <stdio.h> 50.Ft int 51.Fn setbuf "FILE *stream" "char *buf" 52.Ft int 53.Fn setbuffer "FILE *stream" "char *buf" "size_t size" 54.Ft int 55.Fn setlinebuf "FILE *stream" 56.Ft int 57.Fn setvbuf "FILE *stream" "char *buf" "int mode" "size_t size" 58.Sh DESCRIPTION 59The three types of buffering available are unbuffered, block buffered, 60and line buffered. 61When an output stream is unbuffered, information appears on the 62destination file or terminal as soon as written; 63when it is block buffered many characters are saved up and written as a block; 64when it is line buffered characters are saved up until a newline is 65output or input is read from any stream attached to a terminal device 66(typically stdin). 67The function 68.Xr fflush 3 69may be used to force the block out early. 70(See 71.Xr fclose 3 . ) 72Normally all files are block buffered. 73When the first 74.Tn I/O 75operation occurs on a file, 76.Xr malloc 3 77is called, 78and a buffer is obtained. 79If a stream refers to a terminal 80(as 81.Em stdout 82normally does) it is line buffered. 83The standard error stream 84.Em stderr 85is always unbuffered. 86.Pp 87The 88.Fn setvbuf 89function 90may be used at any time on any open stream 91to change its buffer. 92The 93.Fa mode 94parameter must be one of the following three macros: 95.Bl -tag -width _IOFBF -offset indent 96.It Dv _IONBF 97unbuffered 98.It Dv _IOLBF 99line buffered 100.It Dv _IOFBF 101fully buffered 102.El 103.Pp 104Except for unbuffered files, the 105.Fa buf 106argument should point to a buffer at least 107.Fa size 108bytes long; 109this buffer will be used instead of the current buffer. 110If the argument 111.Fa buf 112is NULL, 113only the mode is affected; 114a new buffer will be allocated on the next read or write operation. 115The 116.Fn setvbuf 117function 118may be used at any time, 119but can only change the mode of a stream 120when it is not ``active'': 121that is, before any 122.Tn I/O , 123or immediately after a call to 124.Xr fflush . 125.Pp 126The other three calls are, in effect, simply aliases 127for calls to 128.Fn setvbuf . 129The 130.Fn setbuf 131function 132is exactly equivalent to the call 133.Pp 134.Dl setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ); 135.Pp 136The 137.Fn setbuffer 138function 139is the same, except that the size of the buffer is up to the caller, 140rather than being determined by the default 141.Dv BUFSIZ . 142The 143.Fn setlinebuf 144function 145is exactly equivalent to the call: 146.Pp 147.Dl setvbuf(stream, (char *)NULL, _IOLBF, 0); 148.Sh SEE ALSO 149.Xr fopen 3 , 150.Xr fclose 3 , 151.Xr fread 3 , 152.Xr malloc 3 , 153.Xr puts 3 , 154.Xr printf 3 155.Sh STANDARDS 156The 157.Fn setbuf 158and 159.Fn setvbuf 160functions 161conform to 162.St -ansiC . 163.Sh BUGS 164The 165.Fn setbuffer 166and 167.Fn setlinebuf 168functions are not portable to versions of 169.Bx 170before 171.Bx 4.2 . 172On 173.Bx 4.2 174and 175.Bx 4.3 176systems, 177.Fn setbuf 178always uses a suboptimal buffer size and should be avoided. 179