feof, ferror, clearerr, fileno - stream status inquiries
Feof returns non-zero when end of file is read on the named input
stream, otherwise zero.
Ferror returns non-zero when an error has occurred reading or writing
the named stream, otherwise zero. Unless cleared by clearerr, the
error indication lasts until the stream is closed.
Clrerr resets the error indication on the named stream.
Fileno returns the integer file descriptor associated with the stream,
These functions are implemented as macros; they cannot be redeclared.