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.\" $FreeBSD$ 38.\" 39.Dd June 4, 1993 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 void 51.Fn setbuf "FILE *stream" "char *buf" 52.Ft void 53.Fn setbuffer "FILE *stream" "char *buf" "int 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 . ) 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.Em stdout 83normally does) it is line buffered. 84The standard error stream 85.Em 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 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 104The 105.Fa size 106parameter 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. 115(If the 116.Fa size 117argument 118is not zero but 119.Fa buf 120is 121.Dv NULL , 122a buffer of the given size will be allocated immediately, 123and released on close. 124This is an extension to ANSI C; 125portable code should use a size of 0 with any 126.Dv NULL 127buffer.) 128.Pp 129The 130.Fn setvbuf 131function may be used at any time, 132but may have peculiar side effects 133(such as discarding input or flushing output) 134if the stream is ``active''. 135Portable applications should call it only once on any given stream, 136and before any 137.Tn I/O 138is performed. 139.Pp 140The other three calls are, in effect, simply aliases for calls to 141.Fn setvbuf . 142Except for the lack of a return value, the 143.Fn setbuf 144function is exactly equivalent to the call 145.Pp 146.Dl "setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);" 147.Pp 148The 149.Fn setbuffer 150function 151is the same, except that the size of the buffer is up to the caller, 152rather than being determined by the default 153.Dv BUFSIZ . 154The 155.Fn setlinebuf 156function 157is exactly equivalent to the call: 158.Pp 159.Dl "setvbuf(stream, (char *)NULL, _IOLBF, 0);" 160.Sh RETURN VALUES 161The 162.Fn setvbuf 163function returns 0 on success, or 164.Dv EOF 165if the request cannot be honored 166(note that the stream is still functional in this case). 167.Pp 168The 169.Fn setlinebuf 170function returns what the equivalent 171.Fn setvbuf 172would have returned. 173.Sh SEE ALSO 174.Xr fclose 3 , 175.Xr fopen 3 , 176.Xr fread 3 , 177.Xr malloc 3 , 178.Xr printf 3 , 179.Xr puts 3 180.Sh STANDARDS 181The 182.Fn setbuf 183and 184.Fn setvbuf 185functions 186conform to 187.St -ansiC . 188.Sh BUGS 189The 190.Fn setbuffer 191and 192.Fn setlinebuf 193functions are not portable to versions of 194.Bx 195before 196.Bx 4.2 . 197On 198.Bx 4.2 199and 200.Bx 4.3 201systems, 202.Fn setbuf 203always uses a suboptimal buffer size and should be avoided. 204