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

12       fdopen — associate a stream with a file descriptor
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SYNOPSIS

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

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

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

72       The fdopen() function shall fail if:
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74       EMFILE {STREAM_MAX} streams are currently open in the calling process.
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76       The fdopen() function may fail if:
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78       EBADF  The fildes argument is not a valid file descriptor.
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80       EINVAL The mode argument is not a valid mode.
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82       EMFILE {FOPEN_MAX} streams are currently open in the calling process.
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84       ENOMEM Insufficient space to allocate a buffer.
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86       The following sections are informative.
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EXAMPLES

89       None.
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APPLICATION USAGE

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

96       The file descriptor  may  have  been  obtained  from  open(),  creat(),
97       pipe(),   dup(),   fcntl(),  or  socket();  inherited  through  fork(),
98       posix_spawn(), or exec; or perhaps obtained by other means.
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100       The meanings of the mode arguments of fdopen() and fopen() differ. With
101       fdopen(),  open for write (w or w+) does not truncate, and append (a or
102       a+) cannot create for writing. The mode argument formats that include a
103       b are allowed for consistency with the ISO C standard function fopen().
104       The b has no effect on the resulting stream.  Although  not  explicitly
105       required  by  this  volume  of  POSIX.1‐2017,  a good implementation of
106       append (a) mode would cause the O_APPEND flag to be set.
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FUTURE DIRECTIONS

109       None.
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SEE ALSO

112       Section  2.5.1,  Interaction  of  File  Descriptors  and  Standard  I/O
113       Streams,   fclose(),  fmemopen(),  fopen(),  open(),  open_memstream(),
114       posix_spawn(), socket()
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116       The Base Definitions volume of POSIX.1‐2017, <stdio.h>
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COPYRIGHT

119       Portions of this text are reprinted and reproduced in  electronic  form
120       from  IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
121       table Operating System Interface (POSIX), The Open Group Base  Specifi‐
122       cations  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of
123       Electrical and Electronics Engineers, Inc and The Open Group.   In  the
124       event of any discrepancy between this version and the original IEEE and
125       The Open Group Standard, the original IEEE and The Open Group  Standard
126       is  the  referee document. The original Standard can be obtained online
127       at http://www.opengroup.org/unix/online.html .
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129       Any typographical or formatting errors that appear  in  this  page  are
130       most likely to have been introduced during the conversion of the source
131       files to man page format. To report such errors,  see  https://www.ker‐
132       nel.org/doc/man-pages/reporting_bugs.html .
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136IEEE/The Open Group                  2017                           FDOPEN(3P)