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FOPEN(3C)							     FOPEN(3C)

NAME
       fopen - open a stream

SYNOPSIS
       #include <stdio.h>

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

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

       The argument mode points to a string beginning with one of the  follow‐
       ing base sequences:

       r
			   Open file for reading.

       w
			   Truncate  to	 zero  length or create file for writ‐
			   ing.

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

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

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

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

       In addition to the base sequences for the mode  argument	 above,	 three
       additional  flags  are  supported via the b character, the e character,
       and the x character.  Order of these additional flags (including the +)
       does not matter.

       The  character  b has no effect, but is allowed for ISO C standard con‐
       formance (see standards(5)). Opening a file with read mode  (r  as  the
       first  character in the mode argument) fails if the file does not exist
       or cannot be read.

       The character e will cause the underlying file descriptor to be	opened
       with the O_CLOEXEC flag as described in open(2).

       The  character  x  will attempt to open the specified file exclusively.
       This is the same behavior as  opening  the  underlying  file  with  the
       O_EXCL flag as described in open(2).

       Opening	a  file with append mode (a as the first character in the mode
       argument) causes all subsequent writes to the file to be forced to  the
       then current end-of-file, regardless of intervening calls to fseek(3C).
       If two separate processes open the same file for append,	 each  process
       may  write  freely  to the file without fear of destroying output being
       written by the other.  The output from the two processes will be inter‐
       mixed in the file in the order in which it is written.

       When  a file is opened with update mode (+ as the second or third char‐
       acter in the mode argument), both input and output may be performed  on
       the associated stream. However, output must not be directly followed by
       input without an intervening call to fflush(3C) or to a file  position‐
       ing  function  (	 fseek(3C), fsetpos(3C) or rewind(3C)), and input must
       not be 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 deter‐
       mined  not to refer to an interactive device. The error and end-of-file
       indicators for the stream are cleared.

       If mode begins with w or a and the file did not previously exist,  upon
       successful  completion,	fopen()	 function  will	 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 begins with w and the file did previously exist, upon success‐
       ful completion, fopen() will mark for update the st_ctime and  st_mtime
       fields of the file.  The fopen() function will allocate a file descrip‐
       tor as open(2) does.

       Normally, 32-bit applications return an EMFILE error when attempting to
       associate  a  stream  with  a file accessed by a file descriptor with a
       value greater than 255. If the last character  of  mode	is  F,	32-bit
       applications will be allowed to associate a stream with a file accessed
       by a file descriptor with a value greater  than	255.  A	 FILE  pointer
       obtained in this way must never be used by any code that might directly
       access fields in the FILE structure. If the fields in the  FILE	struc‐
       ture  are  used directly by 32-bit applications when the last character
       of mode is F, data corruption could occur. See  the  USAGE  section  of
       this manual page and the enable_extended_FILE_stdio(3C) manual page for
       other options for enabling the extended FILE facility.

       In 64-bit applications, the last character of mode is silently  ignored
       if  it  is  F.	64-bit	applications are always allowed to associate a
       stream with a file accessed by a file descriptor with any value.

       The largest value that can be represented correctly  in	an  object  of
       type  off_t  will be established as the offset maximum in the open file
       description.

RETURN VALUES
       Upon successful completion, fopen() returns a  pointer  to  the	object
       controlling  the	 stream.   Otherwise,  a  null pointer is returned and
       errno is set to indicate the error.

       The fopen() function may fail and not set errno if there	 are  no  free
       stdio streams.

ERRORS
       The fopen() function will fail if:

       EACCES
		       Search  permission is denied on a component of the path
		       prefix, or the file exists and the  permissions	speci‐
		       fied 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 the execution of fopen().

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

       ELOOP
		       Too many symbolic links were encountered	 in  resolving
		       path.

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

       ENAMETOOLONG
		       The length of the filename exceeds PATH_MAX or a	 path‐
		       name 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
		       it 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 current value of the file position cannot be repre‐
		       sented correctly in an object of type fpos_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.

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

		       {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.

USAGE
       A process is allowed to have at least {FOPEN_MAX} stdio streams open at
       a time. For 32-bit applications, however, the underlying ABIs  formerly
       required	 that  no file descriptor used to access the file underlying a
       stdio stream have a value greater than 255. To maintain binary compati‐
       bility  with  earlier  Solaris  releases,  this	limit still constrains
       32-bit applications. However, when a 32-bit application is  aware  that
       no  code	 that  has access to the FILE pointer returned by fopen() will
       use the FILE pointer to directly access any fields in the  FILE	struc‐
       ture,  the  F  character	 can be used as the last character in the mode
       argument to circumvent this limit. Because it could lead to  data  cor‐
       ruption,	 the  F	 character  in	mode  must never be used when the FILE
       pointer might later be used by binary code unknown to the user.	The  F
       character in mode is intended to be used by library functions that need
       a FILE pointer to access data to process a user	request,  but  do  not
       need  to	 pass  the  FILE pointer back to the user. 32-bit applications
       that have been inspected can use the extended FILE facility to  circum‐
       vent  this  limit if the inspection shows that no FILE pointers will be
       used to directly access FILE structure contents.

       The fopen() function has a transitional interface for 64-bit file  off‐
       sets.  See lf64(5).

ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:

       ┌────────────────────┬─────────────────┐
       │  ATTRIBUTE TYPE    │ ATTRIBUTE VALUE │
       ├────────────────────┼─────────────────┤
       │Interface Stability │ See below.      │
       ├────────────────────┼─────────────────┤
       │MT-Level	    │ MT-Safe	      │
       └────────────────────┴─────────────────┘

       The F character in the mode argument is Evolving. In all other respects
       this function is Standard.

SEE ALSO
       enable_extended_FILE_stdio(3C),	fclose(3C),  fdopen(3C),   fflush(3C),
       freopen(3C),  fsetpos(3C), rewind(3C), open(2), attributes(5), lf64(5),
       standards(5)

				 Nov 06, 2013			     FOPEN(3C)
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