stdio/FreeBSD/setbuf.3

   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: src/lib/libc/stdio/setbuf.3,v 1.15 2004/08/24 21:48:21 alfred Exp $
  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
  61 The three types of buffering available are unbuffered, block buffered,
  62 and line buffered.
  63 When an output stream is unbuffered, information appears on the
  64 destination file or terminal as soon as written;
  65 when it is block buffered many characters are saved up and written as a block;
  66 when it is line buffered characters are saved up until a newline is
  67 output or input is read from any stream attached to a terminal device
  68 (typically
  69 .Dv stdin ) .
  70 The function
  71 .Xr fflush 3
  72 may be used to force the block out early.
  73 (See
  74 .Xr fclose 3 . )
  75 .Pp
  76 Normally all files are block buffered.
  77 When the first
  78 .Tn I/O
  79 operation occurs on a file,
  80 .Xr malloc 3
  81 is called,
  82 and an optimally-sized buffer is obtained.
  83 If a stream refers to a terminal
  84 (as
  85 .Dv stdout
  86 normally does) it is line buffered.
  87 The standard error stream
  88 .Dv stderr
  89 is always unbuffered.
  90 .Pp
  91 The
  92 .Fn setvbuf
  93 function
  94 may be used to alter the buffering behavior of a stream.
  95 The
  96 .Fa mode
  97 argument must be one of the following three macros:
  98 .Bl -tag -width _IOFBF -offset indent
  99 .It Dv _IONBF
 100 unbuffered
 101 .It Dv _IOLBF
 102 line buffered
 103 .It Dv _IOFBF
 104 fully buffered
 105 .El
 106 .Pp
 107 The
 108 .Fa size
 109 argument may be given as zero
 110 to obtain deferred optimal-size buffer allocation as usual.
 111 If it is not zero,
 112 then except for unbuffered files, the
 113 .Fa buf
 114 argument should point to a buffer at least
 115 .Fa size
 116 bytes long;
 117 this buffer will be used instead of the current buffer.
 118 If
 119 .Fa buf
 120 is not NULL, it is the caller's responsibility to
 121 .Xr free 3
 122 this buffer after closing the stream.
 123 (If the
 124 .Fa size
 125 argument
 126 is not zero but
 127 .Fa buf
 128 is
 129 .Dv NULL ,
 130 a buffer of the given size will be allocated immediately,
 131 and released on close.
 132 This is an extension to ANSI C;
 133 portable code should use a size of 0 with any
 134 .Dv NULL
 135 buffer.)
 136 .Pp
 137 The
 138 .Fn setvbuf
 139 function may be used at any time,
 140 but may have peculiar side effects
 141 (such as discarding input or flushing output)
 142 if the stream is ``active''.
 143 Portable applications should call it only once on any given stream,
 144 and before any
 145 .Tn I/O
 146 is performed.
 147 .Pp
 148 The other three calls are, in effect, simply aliases for calls to
 149 .Fn setvbuf .
 150 Except for the lack of a return value, the
 151 .Fn setbuf
 152 function is exactly equivalent to the call
 153 .Pp
 154 .Dl "setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);"
 155 .Pp
 156 The
 157 .Fn setbuffer
 158 function
 159 is the same, except that the size of the buffer is up to the caller,
 160 rather than being determined by the default
 161 .Dv BUFSIZ .
 162 The
 163 .Fn setlinebuf
 164 function
 165 is exactly equivalent to the call:
 166 .Pp
 167 .Dl "setvbuf(stream, (char *)NULL, _IOLBF, 0);"
 168 .Sh RETURN VALUES
 169 The
 170 .Fn setvbuf
 171 function returns 0 on success, or
 172 .Dv EOF
 173 if the request cannot be honored
 174 (note that the stream is still functional in this case).
 175 .Pp
 176 The
 177 .Fn setlinebuf
 178 function returns what the equivalent
 179 .Fn setvbuf
 180 would have returned.
 181 .Sh SEE ALSO
 182 .Xr fclose 3 ,
 183 .Xr fopen 3 ,
 184 .Xr fread 3 ,
 185 .Xr malloc 3 ,
 186 .Xr printf 3 ,
 187 .Xr puts 3
 188 .Sh STANDARDS
 189 The
 190 .Fn setbuf
 191 and
 192 .Fn setvbuf
 193 functions
 194 conform to
 195 .St -isoC .
 196 .Sh BUGS
 197 The
 198 .Fn setbuffer
 199 and
 200 .Fn setlinebuf
 201 functions are not portable to versions of
 202 .Bx
 203 before
 204 .Bx 4.2 .
 205 On
 206 .Bx 4.2
 207 and
 208 .Bx 4.3
 209 systems,
 210 .Fn setbuf
 211 always uses a suboptimal buffer size and should be avoided.