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 42.Sh NAME 43.Nm setbuf , 44.Nm setbuffer , 45.Nm setlinebuf , 46.Nm setvbuf 47.Nd stream buffering operations 48.Sh LIBRARY 49.Lb libc 50.Sh SYNOPSIS 51.In stdio.h 52.Ft void 53.Fn setbuf "FILE * restrict stream" "char * restrict buf" 54.Ft void 55.Fn setbuffer "FILE *stream" "char *buf" "int size" 56.Ft int 57.Fn setlinebuf "FILE *stream" 58.Ft int 59.Fn setvbuf "FILE * restrict stream" "char * restrict buf" "int mode" "size_t size" 60.Sh DESCRIPTION 61The three types of buffering available are unbuffered, block buffered, 62and line buffered. 63When an output stream is unbuffered, information appears on the 64destination file or terminal as soon as written; 65when it is block buffered many characters are saved up and written as a block; 66when it is line buffered characters are saved up until a newline is 67output or input is read from any stream attached to a terminal device 68(typically 69.Dv 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.Dv stdout 86normally does) it is line buffered. 87The standard error stream 88.Dv 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 97argument 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 109argument 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. 118If 119.Fa buf 120is not 121.Dv NULL , 122it is the caller's responsibility to 123.Xr free 3 124this buffer after closing the stream. 125(If the 126.Fa size 127argument 128is not zero but 129.Fa buf 130is 131.Dv NULL , 132a buffer of the given size will be allocated immediately, 133and released on close. 134This is an extension to ANSI C; 135portable code should use a size of 0 with any 136.Dv NULL 137buffer.) 138.Pp 139The 140.Fn setvbuf 141function may be used at any time, 142but may have peculiar side effects 143(such as discarding input or flushing output) 144if the stream is ``active''. 145Portable applications should call it only once on any given stream, 146and before any 147.Tn I/O 148is performed. 149.Pp 150The other three calls are, in effect, simply aliases for calls to 151.Fn setvbuf . 152Except for the lack of a return value, the 153.Fn setbuf 154function is exactly equivalent to the call 155.Pp 156.Dl "setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);" 157.Pp 158The 159.Fn setbuffer 160function 161is the same, except that the size of the buffer is up to the caller, 162rather than being determined by the default 163.Dv BUFSIZ . 164The 165.Fn setlinebuf 166function 167is exactly equivalent to the call: 168.Pp 169.Dl "setvbuf(stream, (char *)NULL, _IOLBF, 0);" 170.Sh RETURN VALUES 171The 172.Fn setvbuf 173function returns 0 on success, or 174.Dv EOF 175if the request cannot be honored 176(note that the stream is still functional in this case). 177.Pp 178The 179.Fn setlinebuf 180function returns what the equivalent 181.Fn setvbuf 182would have returned. 183.Sh SEE ALSO 184.Xr fclose 3 , 185.Xr fopen 3 , 186.Xr fread 3 , 187.Xr malloc 3 , 188.Xr printf 3 , 189.Xr puts 3 190.Sh STANDARDS 191The 192.Fn setbuf 193and 194.Fn setvbuf 195functions 196conform to 197.St -isoC . 198.Sh BUGS 199The 200.Fn setbuffer 201and 202.Fn setlinebuf 203functions are not portable to versions of 204.Bx 205before 206.Bx 4.2 . 207On 208.Bx 4.2 209and 210.Bx 4.3 211systems, 212.Fn setbuf 213always uses a suboptimal buffer size and should be avoided. 214