fopen, fdopen, freopen - stream open functions
Standard C Library (libc, -lc)
#include <stdio.h>
FILE *
fopen(const char *path, const char *mode);
FILE *
fdopen(int fildes, const char *mode);
FILE *
freopen(const char *path, const char *mode, FILE * restrict stream);
The fopen() function opens the file whose name is the string pointed to
by path and associates a stream with it.
The argument mode points to a string beginning with one of the following
sequences (Additional characters may follow these sequences.):
``r'' Open text file for reading.
``r+'' Open for reading and writing.
``w'' Truncate file to zero length or create text file for writing.
``w+'' Open for reading and writing. The file is created if it does not
exist, otherwise it is truncated.
``a'' Append; open for writing. The file is created if it does not
exist.
``a+'' Append; open for reading and writing. The file is created if it
does not exist.
The 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.
The letter ``f'' in the mode string restricts fopen to regular files; if
the file opened is not a regular file, fopen() will fail. This is a non
ANSI X3.159-1989 (``ANSI C'') extension.
Any created files will have mode "S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP |
S_IROTH | S_IWOTH" (0666), as modified by the process' umask value (see
umask(2)).
Opening a file with append mode causes all subsequent writes to it to be
forced to the then current end of file, regardless of intervening repositioning
of the stream.
The fopen() and freopen() functions initially position the stream at the
start of the file unless the file is opened with append mode, in which
case the stream is initially positioned at the end of the file.
The fdopen() function associates a stream with the existing file descriptor,
fildes. The mode of the stream must be compatible with the mode of
the file descriptor. The stream is positioned at the file offset of the
file descriptor.
The freopen() function opens the file whose name is the string pointed to
by path and associates the stream pointed to by stream with it. The
original stream (if it exists) is closed. The mode argument is used just
as in the fopen() function. The primary use of the freopen() function is
to change the file associated with a standard text stream (stderr, stdin,
or stdout).
Upon successful completion fopen(), fdopen() and freopen() return a FILE
pointer. Otherwise, NULL is returned and the global variable errno is
set to indicate the error.
[EINVAL] The mode provided to fopen(), fdopen(), or freopen()
was invalid.
[EFTYPE] The file is not a regular file and the character ``f''
is specified in the mode.
The fopen(), fdopen() and freopen() functions may also fail and set errno
for any of the errors specified for the routine malloc(3).
The fopen() function may also fail and set errno for any of the errors
specified for the routine open(2).
The fdopen() function may also fail and set errno for any of the errors
specified for the routine fcntl(2).
The freopen() function may also fail and set errno for any of the errors
specified for the routines open(2), fclose(3) and fflush(3).
open(2), fclose(3), fseek(3), funopen(3)
The fopen() and freopen() functions conform to ANSI X3.159-1989
(``ANSI C''). The fdopen() function conforms to ISO/IEC 9945-1:1990
(``POSIX.1'').
BSD June 4, 1993 BSD
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