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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 differ (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 imple-
       mentation.
       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 last data access timestamp 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 shall fail if:
       EMFILE {STREAM_MAX} streams are currently open in the calling process.
       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.
       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(),   fcntl(),  or  socket();  inherited  through  fork(),
       posix_spawn(), or exec; or perhaps obtained by other means.
       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  POSIX.1-2008,  a good implementation of
       append (a) mode would cause the O_APPEND flag to be set.
FUTURE DIRECTIONS
       None.
SEE ALSO
       Section  2.5.1,  Interaction  of  File  Descriptors  and  Standard  I/O
       Streams,   fclose(),  fmemopen(),  fopen(),  open(),  open_memstream(),
       posix_spawn(), socket()
       The Base Definitions volume of POSIX.1-2008, <stdio.h>
COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) 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.unix.org/online.html .
       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                           FDOPEN(3P)