======Synopsis:======
$[[ferror]](<<file descriptor>>)

======Technical:======
This function returns non-zero if an error has occurred on the 
//file descriptor// since the last [[read]], because the [[read]]
and [[readb]] functions clear the //file descriptor//s error code.

When the [[read]] or [[readb]] function return the empty string, that
is caused either by an error, an eof, or a blank line.  This function
will tell you if it was an error.  The [[eof]] function will tell you
if it was an end of file.

The //file descriptor// must have been a value previously returned by 
the [[open]] function. 

======Returns:======
|-1   |Error: //file descriptor// was not previously returned by [[open]]|
| 0   |no error has occurred since the last [[read]]|
| 1   |an error has occurred since the last [[read]]|