1FILENO(3P)                 POSIX Programmer's Manual                FILENO(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       fileno - map a stream pointer to a file descriptor
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SYNOPSIS

15       #include <stdio.h>
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17       int fileno(FILE *stream);
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DESCRIPTION

21       The fileno() function shall return the integer file descriptor  associ‐
22       ated with the stream pointed to by stream.
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RETURN VALUE

25       Upon  successful completion, fileno() shall return the integer value of
26       the file descriptor associated with stream.  Otherwise,  the  value  -1
27       shall be returned and errno set to indicate the error.
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ERRORS

30       The fileno() function may fail if:
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32       EBADF  The stream argument is not a valid stream.
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35       The following sections are informative.
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EXAMPLES

38       None.
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APPLICATION USAGE

41       None.
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RATIONALE

44       Without  some  specification  of  which file descriptors are associated
45       with these streams, it is impossible for an application to set  up  the
46       streams for another application it starts with fork() and exec. In par‐
47       ticular, it would not be possible to write a portable version of the sh
48       command interpreter (although there may be other constraints that would
49       prevent that portability).
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FUTURE DIRECTIONS

52       None.
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SEE ALSO

55       Interaction of File Descriptors and  Standard  I/O  Streams,  fdopen(),
56       fopen(),  stdin(), the Base Definitions volume of IEEE Std 1003.1-2001,
57       <stdio.h>
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60       Portions of this text are reprinted and reproduced in  electronic  form
61       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
62       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
63       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
64       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
65       event of any discrepancy between this version and the original IEEE and
66       The Open Group Standard, the original IEEE and The Open Group  Standard
67       is  the  referee document. The original Standard can be obtained online
68       at http://www.opengroup.org/unix/online.html .
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72IEEE/The Open Group                  2003                           FILENO(3P)
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