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



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

NAME
       fdopen - associate a stream with a file descriptor

SYNOPSIS
       #include <stdio.h>

       FILE *fdopen(int fildes, const char *mode);


DESCRIPTION
       The fdopen() function shall associate a stream with a file descriptor.

       The mode argument is a character string having one of the following values:

       r or rb
              Open a file for reading.

       w or wb
              Open a file for writing.

       a or ab
              Open a file for writing at end-of-file.

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

       w+ or wb+ or w+b
              Open a file for update (reading and writing).

       a+ or ab+ or a+b
              Open a file for update (reading and writing) at end-of-file.


       The meaning of these flags is exactly as specified in fopen(), except that modes beginning with w shall not cause trunca-
       tion of the file.

       Additional values for the mode argument may be supported by an implementation.

       The application shall ensure that the mode of the stream as expressed by the mode argument is allowed by the file  access
       mode  of  the open file description to which fildes refers. The file position indicator associated with the new stream is
       set to the position indicated by the file offset associated with the file descriptor.

       The error and end-of-file indicators for the stream shall be cleared.  The fdopen() function may cause the st_atime field
       of the underlying file to be marked for update.

       If fildes refers to a shared memory object, the result of the fdopen() function is unspecified.

       If fildes refers to a typed memory object, the result of the fdopen() function is unspecified.

       The  fdopen()  function  shall  preserve the offset maximum previously set for the open file description corresponding to
       fildes.

RETURN VALUE
       Upon successful completion, fdopen() shall return a pointer to a stream; otherwise, a null pointer shall be returned  and
       errno set to indicate the error.

ERRORS
       The fdopen() function may fail if:

       EBADF  The fildes argument is not a valid file descriptor.

       EINVAL The mode argument is not a valid mode.

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

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

       ENOMEM Insufficient space to allocate a buffer.


       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       File  descriptors  are  obtained  from  calls  like open(), dup(), creat(), or pipe(), which open files but do not return
       streams.

RATIONALE
       The file descriptor may have been obtained from open(), creat(), pipe(), dup(), or fcntl(); inherited through  fork()  or
       exec; or perhaps obtained by implementation-defined means, such as the 4.3 BSD socket() call.

       The  meanings  of  the  mode  arguments of fdopen() and fopen() differ.  With fdopen(), open for write (w or w+) does not
       truncate, and append (a or a+) cannot create for writing. The mode argument formats that include a b are allowed for con-
       sistency  with  the ISO C standard function fopen(). The b has no effect on the resulting stream. Although not explicitly
       required by this volume of IEEE Std 1003.1-2001, a good implementation of append (a) mode would cause the  O_APPEND  flag
       to be set.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Interaction  of  File  Descriptors  and  Standard  I/O Streams, fclose(), fopen(), open(), 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, Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                    FDOPEN(3P)