fileno(3) Library Functions Manual fileno(3) NAME fileno - obtain file descriptor of a stdio stream LIBRARY Standard C library (libc, -lc) 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 in- teger file descriptor used to implement this stream. The file descrip- tor 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 at- tributes(7). ┌────────────────────────────────────────────┬───────────────┬─────────┐ │Interface │ Attribute │ Value │ ├────────────────────────────────────────────┼───────────────┼─────────┤ │fileno() │ Thread safety │ MT-Safe │ └────────────────────────────────────────────┴───────────────┴─────────┘ STANDARDS The function fileno() conforms to POSIX.1-2001 and POSIX.1-2008. SEE ALSO open(2), fdopen(3), stdio(3), unlocked_stdio(3) Linux man-pages 6.03 2022-12-15 fileno(3)
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