1.\" $NetBSD: fopen.3,v 1.10 2000/01/15 01:11:45 christos 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 <stdio.h> 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 *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. 96In addition the letter ``f'' in the mode string restricts fopen to plain 97files; if the file opened is not a plain file, 98.Fn fopen 99will fail. This is a non 100.St -ansiC 101extension. 102.Pp 103Any created files will have mode 104.Pf \\*q Dv S_IRUSR 105\&| 106.Dv S_IWUSR 107\&| 108.Dv S_IRGRP 109\&| 110.Dv S_IWGRP 111\&| 112.Dv S_IROTH 113\&| 114.Dv S_IWOTH Ns \\*q 115.Pq Li 0666 , 116as modified by the process' 117umask value (see 118.Xr umask 2 ) . 119.Pp 120Opening a file with append mode causes all subsequent writes to it 121to be forced to the then current end of file, regardless of intervening 122repositioning of the stream. 123.Pp 124The 125.Fn fopen 126and 127.Fn freopen 128functions initially position the stream at the start of the file 129unless the file is opened with append mode, 130in which case the stream is initially positioned at the end of the file. 131.Pp 132Reads and writes may be intermixed on read/write streams in any order, 133and do not require an intermediate seek as in previous versions of 134.Em stdio . 135This is not portable to other systems, however; 136.Tn ANSI C 137requires that 138a file positioning function intervene between output and input, unless 139an input operation encounters end-of-file. 140.Pp 141The 142.Fn fdopen 143function associates a stream with the existing file descriptor, 144.Fa fildes . 145The 146.Fa mode 147of the stream must be compatible with the mode of the file descriptor. 148The stream is positioned at the file offset of the file descriptor. 149.Pp 150The 151.Fn freopen 152function 153opens the file whose name is the string pointed to by 154.Fa path 155and associates the stream pointed to by 156.Fa stream 157with it. 158The original stream (if it exists) is closed. 159The 160.Fa mode 161argument is used just as in the 162.Fn fopen 163function. 164The primary use of the 165.Fn freopen 166function 167is to change the file associated with a 168standard text stream 169.Pf ( Em stderr , 170.Em stdin , 171or 172.Em stdout ) . 173.Sh RETURN VALUES 174Upon successful completion 175.Fn fopen , 176.Fn fdopen 177and 178.Fn freopen 179return a 180.Tn FILE 181pointer. 182Otherwise, 183.Dv NULL 184is returned and the global variable 185.Va errno 186is set to indicate the error. 187.Sh ERRORS 188.Bl -tag -width Er 189.It Bq Er EINVAL 190The 191.Fa mode 192provided to 193.Fn fopen , 194.Fn fdopen , 195or 196.Fn freopen 197was invalid. 198.It Bq Er EFTYPE 199The file is not a plain file and the character ``f'' is specified 200in the mode. 201.El 202.Pp 203The 204.Fn fopen , 205.Fn fdopen 206and 207.Fn freopen 208functions 209may also fail and set 210.Va errno 211for any of the errors specified for the routine 212.Xr malloc 3 . 213.Pp 214The 215.Fn fopen 216function 217may also fail and set 218.Va errno 219for any of the errors specified for the routine 220.Xr open 2 . 221.Pp 222The 223.Fn fdopen 224function 225may also fail and set 226.Va errno 227for any of the errors specified for the routine 228.Xr fcntl 2 . 229.Pp 230The 231.Fn freopen 232function 233may also fail and set 234.Va errno 235for any of the errors specified for the routines 236.Xr open 2 , 237.Xr fclose 3 238and 239.Xr fflush 3 . 240.Sh SEE ALSO 241.Xr open 2 , 242.Xr fclose 3 , 243.Xr fseek 3 , 244.Xr funopen 3 245.Sh STANDARDS 246The 247.Fn fopen 248and 249.Fn freopen 250functions 251conform to 252.St -ansiC . 253The 254.Fn fdopen 255function conforms to 256.St -p1003.1-90 . 257