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. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)setbuf.3 8.1 (Berkeley) 6/4/93 33.\" $FreeBSD: src/lib/libc/stdio/setbuf.3,v 1.17 2007/01/09 00:28:07 imp Exp $ 34.\" $DragonFly: src/lib/libc/stdio/setbuf.3,v 1.2 2003/06/17 04:26:46 dillon Exp $ 35.\" 36.Dd June 4, 1993 37.Dt SETBUF 3 38.Os 39.Sh NAME 40.Nm setbuf , 41.Nm setbuffer , 42.Nm setlinebuf , 43.Nm setvbuf 44.Nd stream buffering operations 45.Sh LIBRARY 46.Lb libc 47.Sh SYNOPSIS 48.In stdio.h 49.Ft void 50.Fn setbuf "FILE * restrict stream" "char * restrict buf" 51.Ft void 52.Fn setbuffer "FILE *stream" "char *buf" "int size" 53.Ft int 54.Fn setlinebuf "FILE *stream" 55.Ft int 56.Fn setvbuf "FILE * restrict stream" "char * restrict buf" "int mode" "size_t size" 57.Sh DESCRIPTION 58The three types of buffering available are unbuffered, block buffered, 59and line buffered. 60When an output stream is unbuffered, information appears on the 61destination file or terminal as soon as written; 62when it is block buffered many characters are saved up and written as a block; 63when it is line buffered characters are saved up until a newline is 64output or input is read from any stream attached to a terminal device 65(typically 66.Dv stdin ) . 67The function 68.Xr fflush 3 69may be used to force the block out early. 70(See 71.Xr fclose 3 . ) 72.Pp 73Normally all files are block buffered. 74When the first 75.Tn I/O 76operation occurs on a file, 77.Xr malloc 3 78is called, 79and an optimally-sized buffer is obtained. 80If a stream refers to a terminal 81(as 82.Dv stdout 83normally does) it is line buffered. 84The standard error stream 85.Dv stderr 86is always unbuffered. 87.Pp 88The 89.Fn setvbuf 90function 91may be used to alter the buffering behavior of a stream. 92The 93.Fa mode 94argument 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 104The 105.Fa size 106argument may be given as zero 107to obtain deferred optimal-size buffer allocation as usual. 108If it is not zero, 109then except for unbuffered files, the 110.Fa buf 111argument should point to a buffer at least 112.Fa size 113bytes long; 114this buffer will be used instead of the current buffer. 115If 116.Fa buf 117is not 118.Dv NULL , 119it is the caller's responsibility to 120.Xr free 3 121this buffer after closing the stream. 122(If the 123.Fa size 124argument 125is not zero but 126.Fa buf 127is 128.Dv NULL , 129a buffer of the given size will be allocated immediately, 130and released on close. 131This is an extension to ANSI C; 132portable code should use a size of 0 with any 133.Dv NULL 134buffer.) 135.Pp 136The 137.Fn setvbuf 138function may be used at any time, 139but may have peculiar side effects 140(such as discarding input or flushing output) 141if the stream is ``active''. 142Portable applications should call it only once on any given stream, 143and before any 144.Tn I/O 145is performed. 146.Pp 147The other three calls are, in effect, simply aliases for calls to 148.Fn setvbuf . 149Except for the lack of a return value, the 150.Fn setbuf 151function is exactly equivalent to the call 152.Pp 153.Dl "setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);" 154.Pp 155The 156.Fn setbuffer 157function 158is the same, except that the size of the buffer is up to the caller, 159rather than being determined by the default 160.Dv BUFSIZ . 161The 162.Fn setlinebuf 163function 164is exactly equivalent to the call: 165.Pp 166.Dl "setvbuf(stream, NULL, _IOLBF, 0);" 167.Sh RETURN VALUES 168The 169.Fn setvbuf 170function returns 0 on success, or 171.Dv EOF 172if the request cannot be honored 173(note that the stream is still functional in this case). 174.Pp 175The 176.Fn setlinebuf 177function returns what the equivalent 178.Fn setvbuf 179would have returned. 180.Sh SEE ALSO 181.Xr fclose 3 , 182.Xr fopen 3 , 183.Xr fread 3 , 184.Xr malloc 3 , 185.Xr printf 3 , 186.Xr puts 3 187.Sh STANDARDS 188The 189.Fn setbuf 190and 191.Fn setvbuf 192functions 193conform to 194.St -isoC . 195.Sh BUGS 196The 197.Fn setbuffer 198and 199.Fn setlinebuf 200functions are not portable to versions of 201.Bx 202before 203.Bx 4.2 . 204On 205.Bx 4.2 206and 207.Bx 4.3 208systems, 209.Fn setbuf 210always uses a suboptimal buffer size and should be avoided. 211