1.\" $NetBSD: setbuf.3,v 1.13 2003/08/07 16:43:31 agc Exp $ 2.\" 3.\" Copyright (c) 1980, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" This code is derived from software contributed to Berkeley by 7.\" the American National Standards Committee X3, on Information 8.\" Processing Systems. 9.\" 10.\" Redistribution and use in source and binary forms, with or without 11.\" modification, are permitted provided that the following conditions 12.\" are met: 13.\" 1. Redistributions of source code must retain the above copyright 14.\" notice, this list of conditions and the following disclaimer. 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in the 17.\" documentation and/or other materials provided with the distribution. 18.\" 3. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)setbuf.3 8.1 (Berkeley) 6/4/93 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" "size_t 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 stdin). 66The function 67.Xr fflush 3 68may be used to force the block out early. 69(See 70.Xr fclose 3 . ) 71.Pp 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 an optimally-sized 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 initially unbuffered. 86.Pp 87The 88.Fn setvbuf 89function 90may be used to alter the buffering behavior of a stream. 91The 92.Fa mode 93parameter must be one of the following three macros: 94.Bl -tag -width _IOFBF -offset indent 95.It Dv _IONBF 96unbuffered 97.It Dv _IOLBF 98line buffered 99.It Dv _IOFBF 100fully buffered 101.El 102.Pp 103The 104.Fa size 105parameter may be given as zero 106to obtain deferred optimal-size buffer allocation as usual. 107If it is not zero, 108then except for unbuffered files, the 109.Fa buf 110argument should point to a buffer at least 111.Fa size 112bytes long; 113this buffer will be used instead of the current buffer. 114(If the 115.Fa size 116argument 117is not zero but 118.Fa buf 119is 120.Dv NULL , 121a buffer of the given size will be allocated immediately, 122and released on close. 123This is an extension to ANSI C; 124portable code should use a size of 0 with any 125.Dv NULL 126buffer.) 127.Pp 128The 129.Fn setvbuf 130function may be used at any time, 131but may have peculiar side effects 132(such as discarding input or flushing output) 133if the stream is ``active''. 134Portable applications should call it only once on any given stream, 135and before any 136.Tn I/O 137is performed. 138.Pp 139The other three calls are, in effect, simply aliases for calls to 140.Fn setvbuf . 141Except for the lack of a return value, the 142.Fn setbuf 143function is exactly equivalent to the call 144.Pp 145.Dl "setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);" 146.Pp 147The 148.Fn setbuffer 149function 150is the same, except that the size of the buffer is up to the caller, 151rather than being determined by the default 152.Dv BUFSIZ . 153The 154.Fn setlinebuf 155function 156is exactly equivalent to the call: 157.Pp 158.Dl "setvbuf(stream, (char *)NULL, _IOLBF, 0);" 159.Sh RETURN VALUES 160The 161.Fn setvbuf 162function returns 0 on success, or 163.Dv EOF 164if the request cannot be honored 165(note that the stream is still functional in this case). 166.Pp 167The 168.Fn setlinebuf 169function returns what the equivalent 170.Fn setvbuf 171would have returned. 172.Sh SEE ALSO 173.Xr fclose 3 , 174.Xr fopen 3 , 175.Xr fread 3 , 176.Xr malloc 3 , 177.Xr printf 3 , 178.Xr puts 3 179.Sh STANDARDS 180The 181.Fn setbuf 182and 183.Fn setvbuf 184functions 185conform to 186.St -ansiC . 187.Sh BUGS 188The 189.Fn setbuffer 190and 191.Fn setlinebuf 192functions are not portable to versions of 193.Bx 194before 195.Bx 4.2 . 196On 197.Bx 4.2 198and 199.Bx 4.3 200systems, 201.Fn setbuf 202always uses a suboptimal buffer size and should be avoided. 203