1.\" $NetBSD: fopen.3,v 1.18 2002/10/01 17:24:05 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. All advertising materials mentioning features or use of this software 19.\" must display the following acknowledgement: 20.\" This product includes software developed by the University of 21.\" California, Berkeley and its contributors. 22.\" 4. Neither the name of the University nor the names of its contributors 23.\" may be used to endorse or promote products derived from this software 24.\" without specific prior written permission. 25.\" 26.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36.\" SUCH DAMAGE. 37.\" 38.\" @(#)fopen.3 8.1 (Berkeley) 6/4/93 39.\" 40.Dd June 4, 1993 41.Dt FOPEN 3 42.Os 43.Sh NAME 44.Nm fopen , 45.Nm fdopen , 46.Nm freopen 47.Nd stream open functions 48.Sh LIBRARY 49.Lb libc 50.Sh SYNOPSIS 51.Fd #include \*[Lt]stdio.h\*[Gt] 52.Ft FILE * 53.Fn fopen "const char *path" "const char *mode" 54.Ft FILE * 55.Fn fdopen "int fildes" "const char *mode" 56.Ft FILE * 57.Fn freopen "const char *path" "const char *mode" "FILE * restrict stream" 58.Sh DESCRIPTION 59The 60.Fn fopen 61function 62opens the file whose name is the string pointed to by 63.Fa path 64and associates a stream with it. 65.Pp 66The argument 67.Fa mode 68points to a string beginning with one of the following 69sequences (Additional characters may follow these sequences.): 70.Bl -tag -width indent 71.It Dq Li r 72Open text file for reading. 73.It Dq Li r+ 74Open for reading and writing. 75.It Dq Li w 76Truncate file to zero length or create text file for writing. 77.It Dq Li w+ 78Open for reading and writing. 79The file is created if it does not exist, otherwise it is truncated. 80.It Dq Li a 81Append; open for writing. 82The file is created if it does not exist. 83.It Dq Li a+ 84Append; open for reading and writing. 85The file is created if it does not exist. 86.El 87.Pp 88The 89.Fa mode 90string can also include the letter ``b'' either as a last character or 91as a character between the characters in any of the two-character strings 92described above. 93This is strictly for compatibility with 94.St -ansiC 95and has no effect; the ``b'' is ignored. 96.Pp 97The letter ``f'' in the mode string restricts fopen to regular 98files; if the file opened is not a regular file, 99.Fn fopen 100will fail. 101This is a non 102.St -ansiC 103extension. 104.Pp 105Any created files will have mode 106.Pf \\*q Dv S_IRUSR 107\&| 108.Dv S_IWUSR 109\&| 110.Dv S_IRGRP 111\&| 112.Dv S_IWGRP 113\&| 114.Dv S_IROTH 115\&| 116.Dv S_IWOTH Ns \\*q 117.Pq Li 0666 , 118as modified by the process' 119umask value (see 120.Xr umask 2 ) . 121.Pp 122Opening a file with append mode causes all subsequent writes to it 123to be forced to the then current end of file, regardless of intervening 124repositioning of the stream. 125.Pp 126The 127.Fn fopen 128and 129.Fn freopen 130functions initially position the stream at the start of the file 131unless the file is opened with append mode, 132in which case the stream is initially positioned at the end of the file. 133.\" PR 6072 claims this paragraph is not correct. 134.\" .Pp 135.\" Reads and writes may be intermixed on read/write streams in any order, 136.\" and do not require an intermediate seek as in previous versions of 137.\" .Em stdio . 138.\" This is not portable to other systems, however; 139.\" .Tn ANSI C 140.\" requires that 141.\" a file positioning function intervene between output and input, unless 142.\" an input operation encounters end-of-file. 143.Pp 144The 145.Fn fdopen 146function associates a stream with the existing file descriptor, 147.Fa fildes . 148The 149.Fa mode 150of the stream must be compatible with the mode of the file descriptor. 151The stream is positioned at the file offset of the file descriptor. 152.Pp 153The 154.Fn freopen 155function 156opens the file whose name is the string pointed to by 157.Fa path 158and associates the stream pointed to by 159.Fa stream 160with it. 161The original stream (if it exists) is closed. 162The 163.Fa mode 164argument is used just as in the 165.Fn fopen 166function. 167The primary use of the 168.Fn freopen 169function 170is to change the file associated with a 171standard text stream 172.Pf ( Em stderr , 173.Em stdin , 174or 175.Em stdout ) . 176.Sh RETURN VALUES 177Upon successful completion 178.Fn fopen , 179.Fn fdopen 180and 181.Fn freopen 182return a 183.Tn FILE 184pointer. 185Otherwise, 186.Dv NULL 187is returned and the global variable 188.Va errno 189is set to indicate the error. 190.Sh ERRORS 191.Bl -tag -width Er 192.It Bq Er EINVAL 193The 194.Fa mode 195provided to 196.Fn fopen , 197.Fn fdopen , 198or 199.Fn freopen 200was invalid. 201.It Bq Er EFTYPE 202The file is not a regular file and the character ``f'' is specified 203in the mode. 204.El 205.Pp 206The 207.Fn fopen , 208.Fn fdopen 209and 210.Fn freopen 211functions 212may also fail and set 213.Va errno 214for any of the errors specified for the routine 215.Xr malloc 3 . 216.Pp 217The 218.Fn fopen 219function 220may also fail and set 221.Va errno 222for any of the errors specified for the routine 223.Xr open 2 . 224.Pp 225The 226.Fn fdopen 227function 228may also fail and set 229.Va errno 230for any of the errors specified for the routine 231.Xr fcntl 2 . 232.Pp 233The 234.Fn freopen 235function 236may also fail and set 237.Va errno 238for any of the errors specified for the routines 239.Xr open 2 , 240.Xr fclose 3 241and 242.Xr fflush 3 . 243.Sh SEE ALSO 244.Xr open 2 , 245.Xr fclose 3 , 246.Xr fileno 3 , 247.Xr fseek 3 , 248.Xr funopen 3 249.Sh STANDARDS 250The 251.Fn fopen 252and 253.Fn freopen 254functions 255conform to 256.St -ansiC . 257The 258.Fn fdopen 259function conforms to 260.St -p1003.1-90 . 261.Sh CAVEATS 262Proper code using 263.Fn fdopen 264with error checking should 265.Xr close 2 266.Fa fildes 267in case of failure, and 268.Xr fclose 3 269the resulting FILE * in case of success. 270.Bd -literal 271 FILE *file; 272 int fd; 273 274 if ((file = fdopen(fd, "r")) != NULL) { 275 /* perform operations on the FILE * */ 276 fclose(file); 277 } else { 278 /* failure, report the error */ 279 close(fd); 280 } 281.Ed 282