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FOPEN(3P)                  POSIX Programmer's Manual                 FOPEN(3P)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (consult the corresponding Linux manual page for details of Linux behavior), or the interface  may  not  be
       implemented on Linux.

NAME
       fopen - open a stream

SYNOPSIS
       #include <stdio.h>

       FILE *fopen(const char *restrict filename, const char *restrict mode);


DESCRIPTION
       The  fopen() function shall open the file whose pathname is the string pointed to by filename, and associates a
       stream with it.

       The mode argument points to a string. If the string is one of the following, the file shall be  opened  in  the
       indicated mode. Otherwise, the behavior is undefined.

       r or rb
              Open file for reading.

       w or wb
              Truncate to zero length or create file for writing.

       a or ab
              Append; open or create file for writing at end-of-file.

       r+ or rb+ or r+b
              Open file for update (reading and writing).

       w+ or wb+ or w+b
              Truncate to zero length or create file for update.

       a+ or ab+ or a+b
              Append; open or create file for update, writing at end-of-file.


       The  character  'b'  shall  have no effect, but is allowed for ISO C standard conformance.  Opening a file with
       read mode (r as the first character in the mode argument) shall fail if the file does not exist  or  cannot  be
       read.

       Opening  a  file  with  append  mode (a as the first character in the mode argument) shall cause all subsequent
       writes to the file to be forced to the then current end-of-file, regardless of intervening calls to fseek().

       When a file is opened with update mode ( '+' as the second or third character in the mode argument), both input
       and  output may be performed on the associated stream. However, the application shall ensure that output is not
       directly followed by input without an intervening call to fflush() or to a file positioning function ( fseek(),
       fsetpos(),  or  rewind()),  and  input is not directly followed by output without an intervening call to a file
       positioning function, unless the input operation encounters end-of-file.

       When opened, a stream is fully buffered if and only if it can be determined not  to  refer  to  an  interactive
       device. The error and end-of-file indicators for the stream shall be cleared.

       If  mode is w, wb, a, ab, w+, wb+, w+b, a+, ab+, or a+b, and the file did not previously exist, upon successful
       completion, the fopen() function shall mark for update the st_atime, st_ctime, and st_mtime fields of the  file
       and the st_ctime and st_mtime fields of the parent directory.

       If mode is w, wb, w+, wb+, or w+b, and the file did previously exist, upon successful completion, fopen() shall
       mark for update the st_ctime and st_mtime fields of the file.  The  fopen()  function  shall  allocate  a  file
       descriptor as open() does.

       After  a successful call to the fopen() function, the orientation of the stream shall be cleared,  the encoding
       rule shall be cleared,  and the associated mbstate_t object shall be set  to  describe  an  initial  conversion
       state.

       The largest value that can be represented correctly in an object of type off_t shall be established as the off-
       set maximum in the open file description.

RETURN VALUE
       Upon successful completion, fopen() shall return a pointer to the object controlling the stream.  Otherwise,  a
       null pointer shall be returned,  and errno shall be set to indicate the error.

ERRORS
       The fopen() function shall fail if:

       EACCES Search  permission  is  denied on a component of the path prefix, or the file exists and the permissions
              specified by mode are denied, or the file does not exist and write permission is denied for  the  parent
              directory of the file to be created.

       EINTR  A signal was caught during fopen().

       EISDIR The named file is a directory and mode requires write access.

       ELOOP  A loop exists in symbolic links encountered during resolution of the path argument.

       EMFILE {OPEN_MAX} file descriptors are currently open in the calling process.

       ENAMETOOLONG

              The  length  of  the  filename  argument  exceeds  {PATH_MAX}  or  a  pathname  component is longer than
              {NAME_MAX}.

       ENFILE The maximum allowable number of files is currently open in the system.

       ENOENT A component of filename does not name an existing file or filename is an empty string.

       ENOSPC The directory or file system that would contain the new file cannot  be  expanded,  the  file  does  not
              exist, and the file was to be created.

       ENOTDIR
              A component of the path prefix is not a directory.

       ENXIO  The named file is a character special or block special file, and the device associated with this special
              file does not exist.

       EOVERFLOW
              The named file is a regular file and the size of the file cannot be represented correctly in  an  object
              of type off_t.

       EROFS  The named file resides on a read-only file system and mode requires write access.


       The fopen() function may fail if:

       EINVAL The value of the mode argument is not valid.

       ELOOP  More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path argument.

       EMFILE {FOPEN_MAX} streams are currently open in the calling process.

       EMFILE {STREAM_MAX} streams are currently open in the calling process.

       ENAMETOOLONG

              Pathname  resolution of a symbolic link produced an intermediate result whose length exceeds {PATH_MAX}.

       ENOMEM Insufficient storage space is available.

       ETXTBSY
              The file is a pure procedure (shared text) file that is being executed and mode requires write access.


       The following sections are informative.

EXAMPLES
   Opening a File
       The following example tries to open the file named file for  reading.  The  fopen()  function  returns  a  file
       pointer  that  is  used in subsequent fgets() and fclose() calls.  If the program cannot open the file, it just
       ignores it.


              #include <stdio.h>
              ...
              FILE *fp;
              ...
              void rgrep(const char *file)
              {
              ...
                  if ((fp = fopen(file, "r")) == NULL)
                      return;
              ...
              }

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       fclose(), fdopen(), freopen(), the Base Definitions volume of IEEE Std 1003.1-2001, <stdio.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,  Inc  and  The
       Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Stan-
       dard, the original IEEE and The Open Group Standard is the referee  document.  The  original  Standard  can  be
       obtained online at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group                  2003                            FOPEN(3P)