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FOPEN
!!!FOPEN
NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
CONFORMING TO
SEE ALSO
----
!!NAME


fopen, fdopen, freopen - stream open functions
!!SYNOPSIS


__#include __


__FILE *fopen (const char *__''path''__, const char *__''mode''__);__%%%
__FILE *fdopen (int__ ''fildes''__, const char *__''mode''__);__%%%
__FILE *freopen (const char *__''path''__, const char *__''mode''__, FILE *__''stream''__);__
!!DESCRIPTION


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. The stream is positioned at the
beginning of the file.


__r+__


Open for reading and writing. The stream is positioned at
the beginning of the file.


__w__


Truncate file to zero length or create text file for
writing. The stream is positioned at the beginning of the
file.


__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.


__a__


Open for writing. The file is created if it does not exist.
The stream is positioned at the end of the
file.


__a+__


Open for reading and writing. The file is created if it does
not exist. The stream is positioned at the end of the
file.


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 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.)


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).


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
__fseek__ or __fgetpos__ operation between write and
read operations on such a stream. This operation may be an
apparent no-op (as in ''fseek(..., 0L, SEEK_CUR)'' called
for its synchronizing side effect.


The __fdopen__ function associates a stream with the
existing file descriptor, ''fildes''. The ''mode'' of
the stream (one of the values
''fildes'', and the error and
end-of-file indicators are cleared. Modes
''fdopen__ is closed. The result of applying
__fdopen__ to a shared memory object is
undefined.


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'').
!!RETURN VALUE


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.
!!ERRORS


__EINVAL__


The ''mode'' provided to __fopen__, __fdopen__, or
__freopen__ was invalid.


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).
!!CONFORMING TO


The __fopen__ and __freopen__ functions conform to
ANSI X3.159-1989 (``ANSI C''). The __fdopen__ function
conforms to IEEE Std1003.1-1988 (``POSIX.1'').
!!SEE ALSO


open(2), fclose(3),
fileno(3)
----
33 pages link to fopen(3):
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Last edited on Thursday, August 5, 2004 12:32:53 pm by "JimSmith"
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