ferror man page

clearerr, feof, ferror, fileno — check and reset stream status


#include <stdio.h>

void clearerr(FILE *stream);

int feof(FILE *stream);

int ferror(FILE *stream);

int fileno(FILE *stream);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

fileno(): _POSIX_C_SOURCE


The function clearerr() clears the end-of-file and error indicators for the stream pointed to by stream.

The function feof() tests the end-of-file indicator for the stream pointed to by stream, returning nonzero if it is set. The end-of-file indicator can be cleared only by the function clearerr().

The function ferror() tests the error indicator for the stream pointed to by stream, returning nonzero if it is set. The error indicator can be reset only by the clearerr() function.

The function fileno() examines the argument stream and returns its integer file descriptor.

For nonlocking counterparts, see unlocked_stdio(3).


These functions should not fail and do not set the external variable errno. (However, in case fileno() detects that its argument is not a valid stream, it must return -1 and set errno to EBADF.)


For an explanation of the terms used in this section, see attributes(7).

clearerr(), feof(),
ferror(), fileno()
Thread safetyMT-Safe

Conforming to

The functions clearerr(), feof(), and ferror() conform to C89, C99, POSIX.1-2001, and POSIX.1-2008.

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

See Also

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

Referenced By

explain(1), explain(3), explain_feof(3), explain_feof_or_die(3), explain_ferror(3), explain_ferror_or_die(3), explain_fileno(3), explain_fileno_or_die(3), explain_lca2010(1), fgetc(3), fgetln(3), fgetwln(3), fmemopen(3), fopen(3), fread(3), fseek(3), gets(3), getw(3), open_memstream(3), perlfunc(1), puts(3), scanf(3).

Explore man page connections for ferror(3).

clearerr(3), feof(3) and fileno(3) are aliases of ferror(3).