fileno(3)

1fileno(3)                  Library Functions Manual                  fileno(3)
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NAME

6       fileno - obtain file descriptor of a stdio stream
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LIBRARY

9       Standard C library (libc, -lc)
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SYNOPSIS

12       #include <stdio.h>
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14       int fileno(FILE *stream);
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16   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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18       fileno():
19           _POSIX_C_SOURCE
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DESCRIPTION

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

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

36       EBADF  stream is not associated with a file.
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ATTRIBUTES

39       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
40       tributes(7).
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42       ┌────────────────────────────────────────────┬───────────────┬─────────┐
43       │Interface                                   │ Attribute     │ Value   │
44       ├────────────────────────────────────────────┼───────────────┼─────────┤
45       │fileno()                                    │ Thread safety │ MT-Safe │
46       └────────────────────────────────────────────┴───────────────┴─────────┘
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STANDARDS

49       POSIX.1-2008.
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HISTORY

52       POSIX.1-2001.
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