1.\" Copyright (c) 1990, 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.\" Chris Torek and the American National Standards Committee X3, 6.\" on Information 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. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)fopen.3 8.1 (Berkeley) 6/4/93 33.\" $FreeBSD: src/lib/libc/stdio/fopen.3,v 1.20 2007/01/09 00:28:06 imp Exp $ 34.\" 35.Dd February 22, 2018 36.Dt FOPEN 3 37.Os 38.Sh NAME 39.Nm fopen , 40.Nm fdopen , 41.Nm freopen 42.Nd stream open functions 43.Sh LIBRARY 44.Lb libc 45.Sh SYNOPSIS 46.In stdio.h 47.Ft FILE * 48.Fn fopen "const char * restrict path" "const char * restrict mode" 49.Ft FILE * 50.Fn fdopen "int fildes" "const char *mode" 51.Ft FILE * 52.Fn freopen "const char * restrict path" "const char * restrict mode" "FILE * restrict stream" 53.Sh DESCRIPTION 54The 55.Fn fopen 56function 57opens the file whose name is the string pointed to by 58.Fa path 59and associates a stream with it. 60.Pp 61The argument 62.Fa mode 63points to a string beginning with one of the following 64sequences (Additional characters may follow these sequences.): 65.Bl -tag -width indent 66.It Dq Li r 67Open file for reading. 68The stream is positioned at the beginning of the file. 69.It Dq Li w 70Open file for writing. 71Creates the file if it does not already exist, 72truncates the file if it does. 73.It Dq Li a 74Open file for append. 75Creates the file if it does not already exist. 76Seeks to end of the file. 77Subsequent writes to the file will always end up at the then current 78end of file, irrespective of any intervening 79.Xr fseek 3 80or similar operation. 81.El 82.Pp 83Additional flags may modify the primary mode as follows: 84.Bl -tag -width indent 85.It Dq Li + 86The file will be opened for both reading and writing. 87For example 'r+' or 'w+'. 88.It Dq Li x 89The open will fail if the file already exists (C11). 90For example 'wx'. 91.It Dq Li e 92Close-on-exec. 93The underlying descriptor will automatically be closed on any 94.Fn exec 95(glibc compatibility). 96.It Dq Li b 97Binary mode. 98On UNIX systems file reading and writing is always in binary 99mode so this flag has no effect. 100.El 101.Pp 102The 103.Fa mode 104string can also include the letter ``b'' either as a third character or 105as a character between the characters in any of the two-character strings 106described above. 107This is strictly for compatibility with 108.St -isoC-2011 109and has no effect; the ``b'' is ignored. 110.Pp 111Any created files will have mode 112.Pf \\*q Dv S_IRUSR 113\&| 114.Dv S_IWUSR 115\&| 116.Dv S_IRGRP 117\&| 118.Dv S_IWGRP 119\&| 120.Dv S_IROTH 121\&| 122.Dv S_IWOTH Ns \\*q 123.Pq Li 0666 , 124as modified by the process' 125umask value (see 126.Xr umask 2 ) . 127.Pp 128Reads and writes may be intermixed on read/write streams in any order, 129and do not require an intermediate seek as in previous versions of 130.Em stdio . 131This is not portable to other systems, however; 132.Tn ANSI C 133requires that 134a file positioning function intervene between output and input, unless 135an input operation encounters end-of-file. 136.Pp 137The 138.Fn fdopen 139function associates a stream with the existing file descriptor, 140.Fa fildes . 141The mode 142of the stream must be compatible with the mode of the file descriptor. 143When the stream is closed via 144.Xr fclose 3 , 145.Fa fildes 146is closed also. 147.Pp 148The 149.Fn freopen 150function 151opens the file whose name is the string pointed to by 152.Fa path 153and associates the stream pointed to by 154.Fa stream 155with it. 156The original stream (if it exists) is closed. 157The 158.Fa mode 159argument is used just as in the 160.Fn fopen 161function. 162.Pp 163If the 164.Fa path 165argument is 166.Dv NULL , 167.Fn freopen 168attempts to re-open the file associated with 169.Fa stream 170with a new mode. 171The new mode must be compatible with the mode that the stream was originally 172opened with: 173.Bl -bullet -offset indent 174.It 175Streams originally opened with mode 176.Dq Li r 177can only be reopened with that same mode. 178.It 179Streams originally opened with mode 180.Dq Li a 181can be reopened with the same mode, or mode 182.Dq Li w . 183.It 184Streams originally opened with mode 185.Dq Li w 186can be reopened with the same mode, or mode 187.Dq Li a . 188.It 189Streams originally opened with mode 190.Dq Li r+ , 191.Dq Li w+ , 192or 193.Dq Li a+ 194can be reopened with any mode. 195.El 196.Pp 197The primary use of the 198.Fn freopen 199function 200is to change the file associated with a 201standard text stream 202.Dv ( stderr , stdin , 203or 204.Dv stdout ) . 205.Sh RETURN VALUES 206Upon successful completion 207.Fn fopen , 208.Fn fdopen 209and 210.Fn freopen 211return a 212.Tn FILE 213pointer. 214Otherwise, 215.Dv NULL 216is returned and the global variable 217.Va errno 218is set to indicate the error. 219.Sh ERRORS 220.Bl -tag -width Er 221.It Bq Er EINVAL 222The 223.Fa mode 224argument 225to 226.Fn fopen , 227.Fn fdopen , 228or 229.Fn freopen 230was invalid. 231.El 232.Pp 233The 234.Fn fopen , 235.Fn fdopen 236and 237.Fn freopen 238functions 239may also fail and set 240.Va errno 241for any of the errors specified for the routine 242.Xr malloc 3 . 243.Pp 244The 245.Fn fopen 246function 247may also fail and set 248.Va errno 249for any of the errors specified for the routine 250.Xr open 2 . 251.Pp 252The 253.Fn fdopen 254function 255may also fail and set 256.Va errno 257for any of the errors specified for the routine 258.Xr fcntl 2 . 259.Pp 260The 261.Fn freopen 262function 263may also fail and set 264.Va errno 265for any of the errors specified for the routines 266.Xr open 2 , 267.Xr fclose 3 268and 269.Xr fflush 3 . 270.Sh SEE ALSO 271.Xr open 2 , 272.Xr fclose 3 , 273.Xr fileno 3 , 274.Xr fseek 3 , 275.Xr funopen 3 276.Sh STANDARDS 277The 278.Fn fopen 279and 280.Fn freopen 281functions 282conform to 283.St -isoC-2011 . 284The 285.Fn fdopen 286function 287conforms to 288.St -p1003.1-88 . 289