[e-lang] Remaining semantic issues

[Bill Frantz]

On 5/31/05, markm at cs.jhu.edu (Mark Miller) wrote:

>I think this is a terribly important question. My general experience is that 
>API designers go to a lot of trouble to distinguish different error cases, so 
>callers could dispatch on them, but that callers invariably do something like
>
>     if (read(...) < 0) {
>         perror(...)
>         // react to a failure to read
>     }
>
>Could you show us some code that dispatches on these errors to do something 
>useful? A few illustrative examples of successful error handling, which depend 
>on what error happened, may teach us all a lot.

The case I have used the most often involves end of file (EOF) detection.  How this appears to the programmer is quite language and library dependant, for example:

* PL/I uses the ON ENDFILE construct, which is like catching an exception.  It is separate from the method used to report I/O errors.

* C returns a negative value, and you must consult errno to determine if it is EOF or some other condition.

* Java throws EOFException, a subclass of IOException.  Note that treating EOF and I/O errors as the same animal is almost always wrong for production quality code.

Cheers - Bill

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