| .\" Copyright (c) 1990, 1991 The Regents of the University of California. |
| .\" All rights reserved. |
| .\" |
| .\" This code is derived from software contributed to Berkeley by |
| .\" Chris Torek and the American National Standards Committee X3, |
| .\" on Information Processing Systems. |
| .\" |
| .\" Redistribution and use in source and binary forms, with or without |
| .\" modification, are permitted provided that the following conditions |
| .\" are met: |
| .\" 1. Redistributions of source code must retain the above copyright |
| .\" notice, this list of conditions and the following disclaimer. |
| .\" 2. Redistributions in binary form must reproduce the above copyright |
| .\" notice, this list of conditions and the following disclaimer in the |
| .\" documentation and/or other materials provided with the distribution. |
| .\" 3. All advertising materials mentioning features or use of this software |
| .\" must display the following acknowledgement: |
| .\" This product includes software developed by the University of |
| .\" California, Berkeley and its contributors. |
| .\" 4. Neither the name of the University nor the names of its contributors |
| .\" may be used to endorse or promote products derived from this software |
| .\" without specific prior written permission. |
| .\" |
| .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND |
| .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
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| .\" @(#)fopen.3 6.8 (Berkeley) 6/29/91 |
| .\" |
| .\" Converted for Linux, Mon Nov 29 15:22:01 1993, faith@cs.unc.edu |
| .\" Modified, aeb, 960421, 970806 |
| .\" Modified, joey, aeb, 2002-01-03 |
| .\" |
| .TH FOPEN 3 2002-01-03 "BSD MANPAGE" "Linux Programmer's Manual" |
| .SH NAME |
| fopen, fdopen, freopen \- stream open functions |
| .SH SYNOPSIS |
| .B #include <stdio.h> |
| .sp |
| .BI "FILE *fopen(const char *" path ", const char *" mode ); |
| .br |
| .BI "FILE *fdopen(int " fildes ", const char *" mode ); |
| .br |
| .BI "FILE *freopen(const char *" path ", const char *" mode ", FILE *" stream ); |
| .SH DESCRIPTION |
| The |
| .BR fopen () |
| function opens the file whose name is the string pointed to by |
| .I path |
| and associates a stream with it. |
| .PP |
| The argument |
| .I mode |
| points to a string beginning with one of the following sequences |
| (Additional characters may follow these sequences.): |
| .TP |
| .B r |
| Open text file for reading. The stream is positioned at the beginning of |
| the file. |
| .TP |
| .B r+ |
| Open for reading and writing. The stream is positioned at the beginning of |
| the file. |
| .TP |
| .B w |
| Truncate file to zero length or create text file for writing. The stream |
| is positioned at the beginning of the file. |
| .TP |
| .B w+ |
| Open for reading and writing. The file is created if it does not exist, |
| otherwise it is truncated. The stream is positioned at the beginning of |
| the file. |
| .TP |
| .B a |
| Open for appending (writing at end of file). The file is created |
| if it does not exist. The stream is positioned at the end of the file. |
| .TP |
| .B a+ |
| Open for reading and appending (writing at end of file). The file |
| is created if it does not exist. |
| The initial file position for reading is at the beginning of the file, |
| but output is always appended to the end of the file. |
| .PP |
| The |
| .I mode |
| string can also include the letter ``b'' either as a last character or as |
| a character between the characters in any of the two-character strings |
| described above. This is strictly for compatibility with ANSI X3.159-1989 |
| (``ANSI C'') and has no effect; the ``b'' is ignored on all POSIX |
| conforming systems, including Linux. |
| (Other systems may treat text files and binary files differently, |
| and adding the ``b'' may be a good idea if you do I/O to a binary |
| file and expect that your program may be ported to non-Unix |
| environments.) |
| .PP |
| Any created files will have mode |
| .BR S_IRUSR \&| S_IWUSR \&| S_IRGRP \&| S_IWGRP \&| S_IROTH \&| S_IWOTH |
| (0666), as modified by the process' umask value (see |
| .BR umask (2)). |
| .PP |
| Reads and writes may be intermixed on read/write streams in any order. |
| Note that ANSI C requires that a file positioning function intervene |
| between output and input, unless an input operation encounters end-of-file. |
| (If this condition is not met, then a read is allowed to return the |
| result of writes other than the most recent.) |
| Therefore it is good practice (and indeed sometimes necessary |
| under Linux) to put an |
| .BR fseek () |
| or |
| .BR fgetpos () |
| operation between write and read operations on such a stream. This |
| operation may be an apparent no-op (as in \fIfseek(..., 0L, |
| SEEK_CUR)\fR called for its synchronizing side effect. |
| .PP |
| Opening a file in append mode (\fBa\fR as the first character of |
| .IR mode ) |
| causes all subsequent write operations to this stream to occur |
| at end-of-file, as if preceded by an |
| .RS |
| fseek(stream,0,SEEK_END); |
| .RE |
| call. |
| .PP |
| The |
| .BR fdopen () |
| function associates a stream with the existing file descriptor, |
| .IR fildes . |
| The |
| .I mode |
| of the stream (one of the values "r", "r+", "w", "w+", "a", "a+") |
| must be compatible with the mode of the file descriptor. |
| The file position indicator of the new stream is set to that |
| belonging to |
| .IR fildes , |
| and the error and end-of-file indicators are cleared. |
| Modes "w" or "w+" do not cause truncation of the file. |
| The file descriptor is not dup'ed, and will be closed when |
| the stream created by |
| .BR fdopen () |
| is closed. |
| The result of applying |
| .BR fdopen () |
| to a shared memory object is undefined. |
| .PP |
| The |
| .BR freopen () |
| function opens the file whose name is the string pointed to by |
| .I path |
| and associates the stream pointed to by |
| .I stream |
| with it. The original stream (if it exists) is closed. The |
| .I mode |
| argument is used just as in the |
| .BR fopen () |
| function. The primary use of the |
| .BR freopen () |
| function is to change the file associated with a standard text stream |
| .IR "" ( stderr ", " stdin ", or " stdout ). |
| .SH "RETURN VALUE" |
| Upon successful completion |
| .BR fopen (), |
| .BR fdopen () |
| and |
| .BR freopen () |
| return a |
| .I FILE |
| pointer. |
| Otherwise, NULL is returned and the global variable |
| .I errno |
| is set to indicate the error. |
| .SH ERRORS |
| .TP |
| .B EINVAL |
| The |
| .I mode |
| provided to |
| .BR fopen (), |
| .BR fdopen (), |
| or |
| .BR freopen () |
| was invalid. |
| .PP |
| The |
| .BR fopen (), |
| .BR fdopen () |
| and |
| .BR freopen () |
| functions may also fail and set |
| .I errno |
| for any of the errors specified for the routine |
| .BR malloc (3). |
| .PP |
| The |
| .BR fopen () |
| function may also fail and set |
| .I errno |
| for any of the errors specified for the routine |
| .BR open (2). |
| .PP |
| The |
| .BR fdopen () |
| function may also fail and set |
| .I errno |
| for any of the errors specified for the routine |
| .BR fcntl (2). |
| .PP |
| The |
| .BR freopen () |
| function may also fail and set |
| .I errno |
| for any of the errors specified for the routines |
| .BR open (2), |
| .BR fclose (3) |
| and |
| .BR fflush (3). |
| .SH "CONFORMING TO" |
| The |
| .BR fopen () |
| and |
| .BR freopen () |
| functions conform to ANSI X3.159-1989 (``ANSI C''). The |
| .BR fdopen () |
| function conforms to IEEE Std1003.1-1988 (``POSIX.1''). |
| .SH "GLIBC EXTENSIONS" |
| The GNU C libary allows the following extension for the string specified in |
| .IR mode : |
| .TP |
| .B x |
| Open the file exclusively |
| (like the |
| .B O_EXCL |
| flag of |
| .BR open (2)). |
| If the file already exists, |
| .BR fopen () |
| fails, and sets |
| .I errno |
| to |
| .BR EEXIST . |
| .\" FIXME: document /,ccs= charset/ |
| .SH "SEE ALSO" |
| .BR open (2), |
| .BR fclose (3), |
| .BR fileno (3) |