fdopen man page on YellowDog

Man page or keyword search:  
man Server   18644 pages
apropos Keyword Search (all sections)
Output format
YellowDog logo
[printable version]

FOPEN(3)		   Linux Programmer's Manual		      FOPEN(3)

NAME
       fopen, fdopen, freopen - stream open functions

SYNOPSIS
       #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 *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  follow‐
       ing 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 appending (writing at end of file).  The file  is  cre‐
	      ated  if it does not exist.  The stream is positioned at the end
	      of the file.

       a+     Open for reading and appending (writing at end  of  file).   The
	      file is created if it does not exist.  The initial file position
	      for reading is at the beginning  of  the	file,  but  output  is
	      always appended to 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 C89 and has no effect; the ``b'' is ignored on all POSIX  conform‐
       ing  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.

       Opening a file in append mode (a as the first character of mode) causes
       all subsequent write operations to this stream to occur at end-of-file,
       as if preceded by an
	      fseek(stream,0,SEEK_END);
       call.

       The fdopen() function  associates  a  stream  with  the	existing  file
       descriptor,  fildes.   The  mode	 of the stream (one of the values "r",
       "r+", "w", "w+", "a", "a+") must be compatible with  the	 mode  of  the
       file  descriptor.  The file position indicator of the new stream is set
       to that belonging to fildes, and the error and  end-of-file  indicators
       are  cleared.   Modes  "w" or "w+" do not cause truncation of the file.
       The file descriptor is not dup'ed, and will be closed when  the	stream
       created	by  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 C89.
	The fdopen() function conforms to POSIX.1-1990.

GLIBC EXTENSIONS
       The GNU C library allows the following extensions for the string speci‐
       fied in mode:

       c (since glibc 2.3.3)
	      Do  not  make  the  open operation, or subsequent read and write
	      operations, thread cancellation points.

       m (since glibc 2.3)
	      Attempt to access the file using mmap(2), rather than I/O system
	      calls  (read(2),	write(2)).   Currently, use of mmap(2) is only
	      attempted for a file opened for reading.

       x      Open the file exclusively (like the O_EXCL flag of open(2)).  If
	      the  file	 already exists, fopen() fails, and sets errno to EEX‐
	      IST.  This flag is ignored for fdopen().

SEE ALSO
       open(2), fclose(3), fileno(3)

BSD MANPAGE			  2006-05-04			      FOPEN(3)
[top]

List of man pages available for YellowDog

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Tweet
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
....................................................................
Vote for polarhome
Free Shell Accounts :: the biggest list on the net