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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 dif-
       fer (consult 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 truncation 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 corre-
       sponding 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  consistency  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 vol-
       ume 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                           FDOPEN(3P)