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FILENO(3) Linux Programmer's Manual FILENO(3)
NAME
fileno - obtain file descriptor of a stdio stream
SYNOPSIS
#include <stdio.h>
int fileno(FILE *stream);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
fileno():
_POSIX_C_SOURCE
DESCRIPTION
The function fileno() examines the argument stream and returns the integer file descriptor used to implement this stream. The file descriptor is still owned by
stream and will be closed when fclose(3) is called. Duplicate the file descriptor with dup(2) before passing it to code that might close it.
For the nonlocking counterpart, see unlocked_stdio(3).
RETURN VALUE
On success, fileno() returns the file descriptor associated with stream. On failure, -1 is returned and errno is set to indicate the error.
ERRORS
EBADF stream is not associated with a file.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
│fileno() │ Thread safety │ MT-Safe │
└──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘
CONFORMING TO
The function fileno() conforms to POSIX.1-2001 and POSIX.1-2008.
SEE ALSO
open(2), fdopen(3), stdio(3), unlocked_stdio(3)
2021-03-22 FILENO(3)