1.\" $NetBSD: fopen.3,v 1.26 2011/06/27 08:21:07 wiz Exp $ 2.\" 3.\" Copyright (c) 1990, 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.\" Chris Torek and the American National Standards Committee X3, 8.\" on Information 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.\" @(#)fopen.3 8.1 (Berkeley) 6/4/93 35.\" 36.Dd June 24, 2011 37.Dt FOPEN 3 38.Os 39.Sh NAME 40.Nm fopen , 41.Nm fdopen , 42.Nm freopen 43.Nd stream open functions 44.Sh LIBRARY 45.Lb libc 46.Sh SYNOPSIS 47.In stdio.h 48.Ft FILE * 49.Fn fopen "const char * restrict path" "const char * restrict mode" 50.Ft FILE * 51.Fn fdopen "int fildes" "const char *mode" 52.Ft FILE * 53.Fn freopen "const char * restrict path" "const char * restrict mode" "FILE * restrict stream" 54.Sh DESCRIPTION 55The 56.Fn fopen 57function 58opens the file whose name is the string pointed to by 59.Fa path 60and associates a stream with it. 61.Pp 62The argument 63.Fa mode 64points to a string beginning with one of the following 65sequences (Additional characters may follow these sequences.): 66.Bl -tag -width indent 67.It Dq Li r 68Open for reading. 69.It Dq Li r+ 70Open for reading and writing. 71.It Dq Li w 72Open for writing. 73Truncate file to zero length or create file. 74.It Dq Li w+ 75Open for reading and writing. 76Truncate file to zero length or create file. 77.It Dq Li a 78Append; open for writing. 79The file is created if it does not exist. 80.It Dq Li a+ 81Append; open for reading and writing. 82The file is created if it does not exist. 83.El 84.Pp 85The 86.Fa mode 87string can also include the letter 88.Dq b 89either as a last character or 90as a character between the characters in any of the two-character strings 91described above. 92This is strictly for compatibility with 93.St -ansiC 94and has no effect; the 95.Dq b 96is ignored. 97.Pp 98The letter 99.Dq f 100in the mode string restricts fopen to regular 101files; if the file opened is not a regular file, 102.Fn fopen 103will fail. 104This is a non 105.St -ansiC 106extension. 107.Pp 108The letter 109.Dq e 110in the mode string sets the close-on-exec flag in the file descriptors of 111the newly opened file files; if the operation fails, 112.Fn fopen 113will fail. 114This is a non 115.St -ansiC 116extension. 117.Pp 118Any created files will have mode 119.Pf \*q Dv S_IRUSR 120\&| 121.Dv S_IWUSR 122\&| 123.Dv S_IRGRP 124\&| 125.Dv S_IWGRP 126\&| 127.Dv S_IROTH 128\&| 129.Dv S_IWOTH Ns \*q 130.Pq Li 0666 , 131as modified by the process' 132umask value (see 133.Xr umask 2 ) . 134.Pp 135Opening a file with append mode causes all subsequent writes to it 136to be forced to the then current end of file, regardless of intervening 137repositioning of the stream. 138.Pp 139The 140.Fn fopen 141and 142.Fn freopen 143functions initially position the stream at the start of the file 144unless the file is opened with append mode, 145in which case the stream is initially positioned at the end of the file. 146.\" PR 6072 claims this paragraph is not correct. 147.\" .Pp 148.\" Reads and writes may be intermixed on read/write streams in any order, 149.\" and do not require an intermediate seek as in previous versions of 150.\" .Em stdio . 151.\" This is not portable to other systems, however; 152.\" .Tn ANSI C 153.\" requires that 154.\" a file positioning function intervene between output and input, unless 155.\" an input operation encounters end-of-file. 156.Pp 157The 158.Fn fdopen 159function associates a stream with the existing file descriptor, 160.Fa fildes . 161The 162.Fa mode 163of the stream must be compatible with the mode of the file descriptor. 164The stream is positioned at the file offset of the file descriptor. 165.Pp 166The 167.Fn freopen 168function 169opens the file whose name is the string pointed to by 170.Fa path 171and associates the stream pointed to by 172.Fa stream 173with it. 174The original stream (if it exists) is closed. 175The 176.Fa mode 177argument is used just as in the 178.Fn fopen 179function. 180The primary use of the 181.Fn freopen 182function 183is to change the file associated with a 184standard text stream 185.Pf ( Em stderr , 186.Em stdin , 187or 188.Em stdout ) . 189.Sh RETURN VALUES 190Upon successful completion 191.Fn fopen , 192.Fn fdopen 193and 194.Fn freopen 195return a 196.Tn FILE 197pointer. 198Otherwise, 199.Dv NULL 200is returned and the global variable 201.Va errno 202is set to indicate the error. 203.Sh ERRORS 204.Bl -tag -width Er 205.It Bq Er EFTYPE 206The file is not a regular file and the character ``f'' is specified 207in the mode. 208.It Bq Er EINVAL 209The 210.Fa mode 211provided to 212.Fn fopen , 213.Fn fdopen , 214or 215.Fn freopen 216was invalid. 217.El 218.Pp 219The 220.Fn fopen , 221.Fn fdopen 222and 223.Fn freopen 224functions 225may also fail and set 226.Va errno 227for any of the errors specified for the routine 228.Xr malloc 3 . 229.Pp 230The 231.Fn fopen 232function 233may also fail and set 234.Va errno 235for any of the errors specified for the routine 236.Xr open 2 . 237.Pp 238The 239.Fn fdopen 240function 241may also fail and set 242.Va errno 243for any of the errors specified for the routine 244.Xr fcntl 2 . 245.Pp 246The 247.Fn freopen 248function 249may also fail and set 250.Va errno 251for any of the errors specified for the routines 252.Xr open 2 , 253.Xr fclose 3 254and 255.Xr fflush 3 . 256.Sh SEE ALSO 257.Xr open 2 , 258.Xr fclose 3 , 259.Xr fileno 3 , 260.Xr fseek 3 , 261.Xr funopen 3 262.Sh STANDARDS 263The 264.Fn fopen 265and 266.Fn freopen 267functions 268conform to 269.St -ansiC . 270The 271.Fn fdopen 272function conforms to 273.St -p1003.1-90 . 274.Sh CAVEATS 275Proper code using 276.Fn fdopen 277with error checking should 278.Xr close 2 279.Fa fildes 280in case of failure, and 281.Xr fclose 3 282the resulting FILE * in case of success. 283.Bd -literal 284 FILE *file; 285 int fd; 286 287 if ((file = fdopen(fd, "r")) != NULL) { 288 /* perform operations on the FILE * */ 289 fclose(file); 290 } else { 291 /* failure, report the error */ 292 close(fd); 293 } 294.Ed 295