1.\" $NetBSD: fopen.3,v 1.9 1999/01/12 15:27:28 kleink 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 third 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 97Any created files will have mode 98.Pf \\*q Dv S_IRUSR 99\&| 100.Dv S_IWUSR 101\&| 102.Dv S_IRGRP 103\&| 104.Dv S_IWGRP 105\&| 106.Dv S_IROTH 107\&| 108.Dv S_IWOTH Ns \\*q 109.Pq Li 0666 , 110as modified by the process' 111umask value (see 112.Xr umask 2 ) . 113.Pp 114Opening a file with append mode causes all subsequent writes to it 115to be forced to the then current end of file, regardless of intervening 116repositioning of the stream. 117.Pp 118The 119.Fn fopen 120and 121.Fn freopen 122functions initially position the stream at the start of the file 123unless the file is opened with append mode, 124in which case the stream is initially positioned at the end of the file. 125.Pp 126Reads and writes may be intermixed on read/write streams in any order, 127and do not require an intermediate seek as in previous versions of 128.Em stdio . 129This is not portable to other systems, however; 130.Tn ANSI C 131requires that 132a file positioning function intervene between output and input, unless 133an input operation encounters end-of-file. 134.Pp 135The 136.Fn fdopen 137function associates a stream with the existing file descriptor, 138.Fa fildes . 139The 140.Fa mode 141of the stream must be compatible with the mode of the file descriptor. 142The stream is positioned at the file offset of the file descriptor. 143.Pp 144The 145.Fn freopen 146function 147opens the file whose name is the string pointed to by 148.Fa path 149and associates the stream pointed to by 150.Fa stream 151with it. 152The original stream (if it exists) is closed. 153The 154.Fa mode 155argument is used just as in the 156.Fn fopen 157function. 158The primary use of the 159.Fn freopen 160function 161is to change the file associated with a 162standard text stream 163.Pf ( Em stderr , 164.Em stdin , 165or 166.Em stdout ) . 167.Sh RETURN VALUES 168Upon successful completion 169.Fn fopen , 170.Fn fdopen 171and 172.Fn freopen 173return a 174.Tn FILE 175pointer. 176Otherwise, 177.Dv NULL 178is returned and the global variable 179.Va errno 180is set to indicate the error. 181.Sh ERRORS 182.Bl -tag -width Er 183.It Bq Er EINVAL 184The 185.Fa mode 186provided to 187.Fn fopen , 188.Fn fdopen , 189or 190.Fn freopen 191was invalid. 192.El 193.Pp 194The 195.Fn fopen , 196.Fn fdopen 197and 198.Fn freopen 199functions 200may also fail and set 201.Va errno 202for any of the errors specified for the routine 203.Xr malloc 3 . 204.Pp 205The 206.Fn fopen 207function 208may also fail and set 209.Va errno 210for any of the errors specified for the routine 211.Xr open 2 . 212.Pp 213The 214.Fn fdopen 215function 216may also fail and set 217.Va errno 218for any of the errors specified for the routine 219.Xr fcntl 2 . 220.Pp 221The 222.Fn freopen 223function 224may also fail and set 225.Va errno 226for any of the errors specified for the routines 227.Xr open 2 , 228.Xr fclose 3 229and 230.Xr fflush 3 . 231.Sh SEE ALSO 232.Xr open 2 , 233.Xr fclose 3 , 234.Xr fseek 3 , 235.Xr funopen 3 236.Sh STANDARDS 237The 238.Fn fopen 239and 240.Fn freopen 241functions 242conform to 243.St -ansiC . 244The 245.Fn fdopen 246function conforms to 247.St -p1003.1-90 . 248