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.\" $DragonFly: src/lib/libc/stdio/setbuf.3,v 1.2 2003/06/17 04:26:46 dillon Exp $ 39.\" 40.Dd June 4, 1993 41.Dt SETBUF 3 42.Os 43.Sh NAME 44.Nm setbuf , 45.Nm setbuffer , 46.Nm setlinebuf , 47.Nm setvbuf 48.Nd stream buffering operations 49.Sh LIBRARY 50.Lb libc 51.Sh SYNOPSIS 52.In stdio.h 53.Ft void 54.Fn setbuf "FILE *stream" "char *buf" 55.Ft void 56.Fn setbuffer "FILE *stream" "char *buf" "int size" 57.Ft int 58.Fn setlinebuf "FILE *stream" 59.Ft int 60.Fn setvbuf "FILE *stream" "char *buf" "int mode" "size_t size" 61.Sh DESCRIPTION 62The three types of buffering available are unbuffered, block buffered, 63and line buffered. 64When an output stream is unbuffered, information appears on the 65destination file or terminal as soon as written; 66when it is block buffered many characters are saved up and written as a block; 67when it is line buffered characters are saved up until a newline is 68output or input is read from any stream attached to a terminal device 69(typically stdin). 70The function 71.Xr fflush 3 72may be used to force the block out early. 73(See 74.Xr fclose 3 . ) 75.Pp 76Normally all files are block buffered. 77When the first 78.Tn I/O 79operation occurs on a file, 80.Xr malloc 3 81is called, 82and an optimally-sized buffer is obtained. 83If a stream refers to a terminal 84(as 85.Em stdout 86normally does) it is line buffered. 87The standard error stream 88.Em stderr 89is always unbuffered. 90.Pp 91The 92.Fn setvbuf 93function 94may be used to alter the buffering behavior of a stream. 95The 96.Fa mode 97parameter must be one of the following three macros: 98.Bl -tag -width _IOFBF -offset indent 99.It Dv _IONBF 100unbuffered 101.It Dv _IOLBF 102line buffered 103.It Dv _IOFBF 104fully buffered 105.El 106.Pp 107The 108.Fa size 109parameter may be given as zero 110to obtain deferred optimal-size buffer allocation as usual. 111If it is not zero, 112then except for unbuffered files, the 113.Fa buf 114argument should point to a buffer at least 115.Fa size 116bytes long; 117this buffer will be used instead of the current buffer. 118(If the 119.Fa size 120argument 121is not zero but 122.Fa buf 123is 124.Dv NULL , 125a buffer of the given size will be allocated immediately, 126and released on close. 127This is an extension to ANSI C; 128portable code should use a size of 0 with any 129.Dv NULL 130buffer.) 131.Pp 132The 133.Fn setvbuf 134function may be used at any time, 135but may have peculiar side effects 136(such as discarding input or flushing output) 137if the stream is ``active''. 138Portable applications should call it only once on any given stream, 139and before any 140.Tn I/O 141is performed. 142.Pp 143The other three calls are, in effect, simply aliases for calls to 144.Fn setvbuf . 145Except for the lack of a return value, the 146.Fn setbuf 147function is exactly equivalent to the call 148.Pp 149.Dl "setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);" 150.Pp 151The 152.Fn setbuffer 153function 154is the same, except that the size of the buffer is up to the caller, 155rather than being determined by the default 156.Dv BUFSIZ . 157The 158.Fn setlinebuf 159function 160is exactly equivalent to the call: 161.Pp 162.Dl "setvbuf(stream, (char *)NULL, _IOLBF, 0);" 163.Sh RETURN VALUES 164The 165.Fn setvbuf 166function returns 0 on success, or 167.Dv EOF 168if the request cannot be honored 169(note that the stream is still functional in this case). 170.Pp 171The 172.Fn setlinebuf 173function returns what the equivalent 174.Fn setvbuf 175would have returned. 176.Sh SEE ALSO 177.Xr fclose 3 , 178.Xr fopen 3 , 179.Xr fread 3 , 180.Xr malloc 3 , 181.Xr printf 3 , 182.Xr puts 3 183.Sh STANDARDS 184The 185.Fn setbuf 186and 187.Fn setvbuf 188functions 189conform to 190.St -isoC . 191.Sh BUGS 192The 193.Fn setbuffer 194and 195.Fn setlinebuf 196functions are not portable to versions of 197.Bx 198before 199.Bx 4.2 . 200On 201.Bx 4.2 202and 203.Bx 4.3 204systems, 205.Fn setbuf 206always uses a suboptimal buffer size and should be avoided. 207