1FILENO(3)                  Linux Programmer's Manual                 FILENO(3)
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NAME

6       fileno - obtain file descriptor of a stdio stream
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SYNOPSIS

9       #include <stdio.h>
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11       int fileno(FILE *stream);
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13   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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15       fileno():
16           _POSIX_C_SOURCE
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DESCRIPTION

19       The  function fileno() examines the argument stream and returns the in‐
20       teger file descriptor used to implement this stream.  The file descrip‐
21       tor  is  still  owned  by  stream  and will be closed when fclose(3) is
22       called.  Duplicate the file descriptor with dup(2) before passing it to
23       code that might close it.
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25       For the nonlocking counterpart, see unlocked_stdio(3).
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RETURN VALUE

28       On  success,  fileno()  returns  the  file  descriptor  associated with
29       stream.  On failure, -1 is returned and errno is set  to  indicate  the
30       error.
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ERRORS

33       EBADF  stream is not associated with a file.
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ATTRIBUTES

36       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
37       tributes(7).
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39       ┌────────────────────────────────────────────┬───────────────┬─────────┐
40       │Interface                                   │ Attribute     │ Value   │
41       ├────────────────────────────────────────────┼───────────────┼─────────┤
42       │fileno()                                    │ Thread safety │ MT-Safe │
43       └────────────────────────────────────────────┴───────────────┴─────────┘
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CONFORMING TO

46       The function fileno() conforms to POSIX.1-2001 and POSIX.1-2008.
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SEE ALSO

49       open(2), fdopen(3), stdio(3), unlocked_stdio(3)
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COLOPHON

52       This page is part of release 5.12 of the Linux  man-pages  project.   A
53       description  of  the project, information about reporting bugs, and the
54       latest    version    of    this    page,    can     be     found     at
55       https://www.kernel.org/doc/man-pages/.
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59                                  2021-03-22                         FILENO(3)
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