1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. 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.\" @(#)setbuf.3 8.1 (Berkeley) 6/4/93 37.\" $FreeBSD: src/lib/libc/stdio/setbuf.3,v 1.5.2.5 2001/12/14 18:33:57 ru Exp $ 38.\" 39.Dd June 4, 1993 40.Dt SETBUF 3 41.Os 42.Sh NAME 43.Nm setbuf , 44.Nm setbuffer , 45.Nm setlinebuf , 46.Nm setvbuf 47.Nd stream buffering operations 48.Sh LIBRARY 49.Lb libc 50.Sh SYNOPSIS 51.In stdio.h 52.Ft void 53.Fn setbuf "FILE *stream" "char *buf" 54.Ft void 55.Fn setbuffer "FILE *stream" "char *buf" "int size" 56.Ft int 57.Fn setlinebuf "FILE *stream" 58.Ft int 59.Fn setvbuf "FILE *stream" "char *buf" "int mode" "size_t size" 60.Sh DESCRIPTION 61The three types of buffering available are unbuffered, block buffered, 62and line buffered. 63When an output stream is unbuffered, information appears on the 64destination file or terminal as soon as written; 65when it is block buffered many characters are saved up and written as a block; 66when it is line buffered characters are saved up until a newline is 67output or input is read from any stream attached to a terminal device 68(typically stdin). 69The function 70.Xr fflush 3 71may be used to force the block out early. 72(See 73.Xr fclose 3 . ) 74.Pp 75Normally all files are block buffered. 76When the first 77.Tn I/O 78operation occurs on a file, 79.Xr malloc 3 80is called, 81and an optimally-sized buffer is obtained. 82If a stream refers to a terminal 83(as 84.Em stdout 85normally does) it is line buffered. 86The standard error stream 87.Em stderr 88is always unbuffered. 89.Pp 90The 91.Fn setvbuf 92function 93may be used to alter the buffering behavior of a stream. 94The 95.Fa mode 96parameter must be one of the following three macros: 97.Bl -tag -width _IOFBF -offset indent 98.It Dv _IONBF 99unbuffered 100.It Dv _IOLBF 101line buffered 102.It Dv _IOFBF 103fully buffered 104.El 105.Pp 106The 107.Fa size 108parameter may be given as zero 109to obtain deferred optimal-size buffer allocation as usual. 110If it is not zero, 111then except for unbuffered files, the 112.Fa buf 113argument should point to a buffer at least 114.Fa size 115bytes long; 116this buffer will be used instead of the current buffer. 117(If the 118.Fa size 119argument 120is not zero but 121.Fa buf 122is 123.Dv NULL , 124a buffer of the given size will be allocated immediately, 125and released on close. 126This is an extension to ANSI C; 127portable code should use a size of 0 with any 128.Dv NULL 129buffer.) 130.Pp 131The 132.Fn setvbuf 133function may be used at any time, 134but may have peculiar side effects 135(such as discarding input or flushing output) 136if the stream is ``active''. 137Portable applications should call it only once on any given stream, 138and before any 139.Tn I/O 140is performed. 141.Pp 142The other three calls are, in effect, simply aliases for calls to 143.Fn setvbuf . 144Except for the lack of a return value, the 145.Fn setbuf 146function is exactly equivalent to the call 147.Pp 148.Dl "setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);" 149.Pp 150The 151.Fn setbuffer 152function 153is the same, except that the size of the buffer is up to the caller, 154rather than being determined by the default 155.Dv BUFSIZ . 156The 157.Fn setlinebuf 158function 159is exactly equivalent to the call: 160.Pp 161.Dl "setvbuf(stream, (char *)NULL, _IOLBF, 0);" 162.Sh RETURN VALUES 163The 164.Fn setvbuf 165function returns 0 on success, or 166.Dv EOF 167if the request cannot be honored 168(note that the stream is still functional in this case). 169.Pp 170The 171.Fn setlinebuf 172function returns what the equivalent 173.Fn setvbuf 174would have returned. 175.Sh SEE ALSO 176.Xr fclose 3 , 177.Xr fopen 3 , 178.Xr fread 3 , 179.Xr malloc 3 , 180.Xr printf 3 , 181.Xr puts 3 182.Sh STANDARDS 183The 184.Fn setbuf 185and 186.Fn setvbuf 187functions 188conform to 189.St -isoC . 190.Sh BUGS 191The 192.Fn setbuffer 193and 194.Fn setlinebuf 195functions are not portable to versions of 196.Bx 197before 198.Bx 4.2 . 199On 200.Bx 4.2 201and 202.Bx 4.3 203systems, 204.Fn setbuf 205always uses a suboptimal buffer size and should be avoided. 206