1.\" $NetBSD: fopen.3,v 1.11 2000/05/17 10:09:35 fair 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.\" PR 6072 claims this paragraph is not correct. 132.\" .Pp 133.\" Reads and writes may be intermixed on read/write streams in any order, 134.\" and do not require an intermediate seek as in previous versions of 135.\" .Em stdio . 136.\" This is not portable to other systems, however; 137.\" .Tn ANSI C 138.\" requires that 139.\" a file positioning function intervene between output and input, unless 140.\" an input operation encounters end-of-file. 141.Pp 142The 143.Fn fdopen 144function associates a stream with the existing file descriptor, 145.Fa fildes . 146The 147.Fa mode 148of the stream must be compatible with the mode of the file descriptor. 149The stream is positioned at the file offset of the file descriptor. 150.Pp 151The 152.Fn freopen 153function 154opens the file whose name is the string pointed to by 155.Fa path 156and associates the stream pointed to by 157.Fa stream 158with it. 159The original stream (if it exists) is closed. 160The 161.Fa mode 162argument is used just as in the 163.Fn fopen 164function. 165The primary use of the 166.Fn freopen 167function 168is to change the file associated with a 169standard text stream 170.Pf ( Em stderr , 171.Em stdin , 172or 173.Em stdout ) . 174.Sh RETURN VALUES 175Upon successful completion 176.Fn fopen , 177.Fn fdopen 178and 179.Fn freopen 180return a 181.Tn FILE 182pointer. 183Otherwise, 184.Dv NULL 185is returned and the global variable 186.Va errno 187is set to indicate the error. 188.Sh ERRORS 189.Bl -tag -width Er 190.It Bq Er EINVAL 191The 192.Fa mode 193provided to 194.Fn fopen , 195.Fn fdopen , 196or 197.Fn freopen 198was invalid. 199.It Bq Er EFTYPE 200The file is not a plain file and the character ``f'' is specified 201in the mode. 202.El 203.Pp 204The 205.Fn fopen , 206.Fn fdopen 207and 208.Fn freopen 209functions 210may also fail and set 211.Va errno 212for any of the errors specified for the routine 213.Xr malloc 3 . 214.Pp 215The 216.Fn fopen 217function 218may also fail and set 219.Va errno 220for any of the errors specified for the routine 221.Xr open 2 . 222.Pp 223The 224.Fn fdopen 225function 226may also fail and set 227.Va errno 228for any of the errors specified for the routine 229.Xr fcntl 2 . 230.Pp 231The 232.Fn freopen 233function 234may also fail and set 235.Va errno 236for any of the errors specified for the routines 237.Xr open 2 , 238.Xr fclose 3 239and 240.Xr fflush 3 . 241.Sh SEE ALSO 242.Xr open 2 , 243.Xr fclose 3 , 244.Xr fseek 3 , 245.Xr funopen 3 246.Sh STANDARDS 247The 248.Fn fopen 249and 250.Fn freopen 251functions 252conform to 253.St -ansiC . 254The 255.Fn fdopen 256function conforms to 257.St -p1003.1-90 . 258