Many of the functions described in this chapter return the value of the
macro EOF
to indicate unsuccessful completion of the operation.
Since EOF
is used to report both end of file and random errors,
it’s often better to use the feof
function to check explicitly
for end of file and ferror
to check for errors. These functions
check indicators that are part of the internal state of the stream
object, indicators set if the appropriate condition was detected by a
previous I/O operation on that stream.
int
EOF ¶This macro is an integer value that is returned by a number of narrow
stream functions to indicate an end-of-file condition, or some other
error situation. With the GNU C Library, EOF
is -1
. In
other libraries, its value may be some other negative number.
This symbol is declared in stdio.h.
int
WEOF ¶This macro is an integer value that is returned by a number of wide
stream functions to indicate an end-of-file condition, or some other
error situation. With the GNU C Library, WEOF
is -1
. In
other libraries, its value may be some other negative number.
This symbol is declared in wchar.h.
int
feof (FILE *stream)
¶Preliminary: | MT-Safe | AS-Safe | AC-Unsafe lock | See POSIX Safety Concepts.
The feof
function returns nonzero if and only if the end-of-file
indicator for the stream stream is set.
This symbol is declared in stdio.h.
int
feof_unlocked (FILE *stream)
¶Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
The feof_unlocked
function is equivalent to the feof
function except that it does not implicitly lock the stream.
This function is a GNU extension.
This symbol is declared in stdio.h.
int
ferror (FILE *stream)
¶Preliminary: | MT-Safe | AS-Safe | AC-Unsafe lock | See POSIX Safety Concepts.
The ferror
function returns nonzero if and only if the error
indicator for the stream stream is set, indicating that an error
has occurred on a previous operation on the stream.
This symbol is declared in stdio.h.
int
ferror_unlocked (FILE *stream)
¶Preliminary: | MT-Safe | AS-Safe | AC-Safe | See POSIX Safety Concepts.
The ferror_unlocked
function is equivalent to the ferror
function except that it does not implicitly lock the stream.
This function is a GNU extension.
This symbol is declared in stdio.h.
In addition to setting the error indicator associated with the stream,
the functions that operate on streams also set errno
in the same
way as the corresponding low-level functions that operate on file
descriptors. For example, all of the functions that perform output to a
stream—such as fputc
, printf
, and fflush
—are
implemented in terms of write
, and all of the errno
error
conditions defined for write
are meaningful for these functions.
For more information about the descriptor-level I/O functions, see
Low-Level Input/Output.