1.\" Copyright (c) 1980, 1991 Regents of the University of California. 2.\" 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 6.10 (Berkeley) 6/29/91 37.\" 38.Dd June 29, 1991 39.Dt SETBUF 3 40.Os BSD 4 41.Sh NAME 42.Nm setbuf , 43.Nm setbuffer , 44.Nm setlinebuf , 45.Nm setvbuf 46.Nd stream buffering operations 47.Sh SYNOPSIS 48.Fd #include <stdio.h> 49.Ft int 50.Fn setbuf "FILE *stream" "char *buf" 51.Ft int 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 *stream" "char *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 . ) 71Normally all files are block buffered. 72When the first 73.Tn I/O 74operation occurs on a file, 75.Xr malloc 3 76is called, 77and a buffer is obtained. 78If a stream refers to a terminal 79(as 80.Em stdout 81normally does) it is line buffered. 82The standard error stream 83.Em stderr 84is always unbuffered. 85.Pp 86The 87.Fn setvbuf 88function 89may be used at any time on any open stream 90to change its buffer. 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 103Except for unbuffered files, the 104.Fa buf 105argument should point to a buffer at least 106.Fa size 107bytes long; 108this buffer will be used instead of the current buffer. 109If the argument 110.Fa buf 111is NULL, 112only the mode is affected; 113a new buffer will be allocated on the next read or write operation. 114The 115.Fn setvbuf 116function 117may be used at any time, 118but can only change the mode of a stream 119when it is not ``active'': 120that is, before any 121.Tn I/O , 122or immediately after a call to 123.Xr fflush . 124.Pp 125The other three calls are, in effect, simply aliases 126for calls to 127.Fn setvbuf . 128The 129.Fn setbuf 130function 131is exactly equivalent to the call 132.Pp 133.Dl setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ); 134.Pp 135The 136.Fn setbuffer 137function 138is the same, except that the size of the buffer is up to the caller, 139rather than being determined by the default 140.Dv BUFSIZ . 141The 142.Fn setlinebuf 143function 144is exactly equivalent to the call: 145.Pp 146.Dl setvbuf(stream, (char *)NULL, _IOLBF, 0); 147.Sh SEE ALSO 148.Xr fopen 3 , 149.Xr fclose 3 , 150.Xr fread 3 , 151.Xr malloc 3 , 152.Xr puts 3 , 153.Xr printf 3 154.Sh STANDARDS 155The 156.Fn setbuf 157and 158.Fn setvbuf 159functions 160conform to 161.St -ansiC . 162.Sh BUGS 163The 164.Fn setbuffer 165and 166.Fn setlinebuf 167functions are not portable to versions of 168.Bx 169before 170.Bx 4.2 . 171On 172.Bx 4.2 173and 174.Bx 4.3 175systems, 176.Fn setbuf 177always uses a suboptimal buffer size and should be avoided. 178