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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 differ (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 fol-
       lowing, 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 stan-
       dard conformance.  Opening a file with read mode (r as the first  char-
       acter  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 oper-
       ation encounters end-of-file.
       When opened, a stream is fully buffered if and only if it can be deter-
       mined  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() func-
       tion 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 direc-
       tory.
       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 conver-
       sion state.
       The largest value that can be represented correctly  in  an  object  of
       type  off_t shall be established as the offset 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 file-
              name 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, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications  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 Standard, 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)