1FDOPEN(3P)                 POSIX Programmer's Manual                FDOPEN(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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NAME

13       fdopen — associate a stream with a file descriptor
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SYNOPSIS

16       #include <stdio.h>
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18       FILE *fdopen(int fildes, const char *mode);
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DESCRIPTION

21       The fdopen() function shall associate a stream with a file descriptor.
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23       The mode argument is a character string having  one  of  the  following
24       values:
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26       r or rb       Open a file for reading.
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28       w or wb       Open a file for writing.
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30       a or ab       Open a file for writing at end-of-file.
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32       r+ or rb+ or r+b
33                     Open a file for update (reading and writing).
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35       w+ or wb+ or w+b
36                     Open a file for update (reading and writing).
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38       a+ or ab+ or a+b
39                     Open  a  file for update (reading and writing) at end-of-
40                     file.
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42       The meaning of these flags is exactly as specified in  fopen(),  except
43       that modes beginning with w shall not cause truncation of the file.
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45       Additional  values  for the mode argument may be supported by an imple‐
46       mentation.
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48       The application shall ensure that the mode of the stream  as  expressed
49       by  the  mode  argument  is allowed by the file access mode of the open
50       file description to which fildes refers. The  file  position  indicator
51       associated  with the new stream is set to the position indicated by the
52       file offset associated with the file descriptor.
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54       The error and end-of-file indicators for the stream shall  be  cleared.
55       The  fdopen()  function may cause the last data access timestamp of the
56       underlying file to be marked for update.
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58       If fildes refers to a shared memory object, the result of the  fdopen()
59       function is unspecified.
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61       If  fildes  refers to a typed memory object, the result of the fdopen()
62       function is unspecified.
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64       The fdopen() function shall preserve the offset maximum previously  set
65       for the open file description corresponding to fildes.
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RETURN VALUE

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

73       The fdopen() function shall fail if:
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75       EMFILE {STREAM_MAX} streams are currently open in the calling process.
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77       The fdopen() function may fail if:
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79       EBADF  The fildes argument is not a valid file descriptor.
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81       EINVAL The mode argument is not a valid mode.
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83       EMFILE {FOPEN_MAX} streams are currently open in the calling process.
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85       ENOMEM Insufficient space to allocate a buffer.
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87       The following sections are informative.
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EXAMPLES

90       None.
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APPLICATION USAGE

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

97       The file descriptor  may  have  been  obtained  from  open(),  creat(),
98       pipe(),   dup(),   fcntl(),  or  socket();  inherited  through  fork(),
99       posix_spawn(), or exec; or perhaps obtained by other means.
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101       The meanings of the mode arguments of fdopen() and fopen() differ. With
102       fdopen(),  open for write (w or w+) does not truncate, and append (a or
103       a+) cannot create for writing. The mode argument formats that include a
104       b are allowed for consistency with the ISO C standard function fopen().
105       The b has no effect on the resulting stream.  Although  not  explicitly
106       required  by  this  volume  of  POSIX.1‐2008,  a good implementation of
107       append (a) mode would cause the O_APPEND flag to be set.
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FUTURE DIRECTIONS

110       None.
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SEE ALSO

113       Section  2.5.1,  Interaction  of  File  Descriptors  and  Standard  I/O
114       Streams,   fclose(),  fmemopen(),  fopen(),  open(),  open_memstream(),
115       posix_spawn(), socket()
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117       The Base Definitions volume of POSIX.1‐2008, <stdio.h>
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COPYRIGHT

120       Portions of this text are reprinted and reproduced in  electronic  form
121       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
122       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
123       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
124       cal and Electronics Engineers,  Inc  and  The  Open  Group.   (This  is
125       POSIX.1-2008  with  the  2013  Technical Corrigendum 1 applied.) In the
126       event of any discrepancy between this version and the original IEEE and
127       The  Open Group Standard, the original IEEE and The Open Group Standard
128       is the referee document. The original Standard can be  obtained  online
129       at http://www.unix.org/online.html .
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131       Any  typographical  or  formatting  errors that appear in this page are
132       most likely to have been introduced during the conversion of the source
133       files  to  man page format. To report such errors, see https://www.ker‐
134       nel.org/doc/man-pages/reporting_bugs.html .
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138IEEE/The Open Group                  2013                           FDOPEN(3P)