In PHP5, should I use Exceptions or trigger_error/set_error_handler ?

Question

What are the pros/cons of doing either way. Is there One Right Way(tm) ?

Answer 1

I love the idea of using exceptions, but I often have third party libraries involved, and then if they don't use exceptions you end up with 3-4 different approaches to the problem! Zend uses exceptions. CakePHP uses a custom error handler, and most PEAR libraries use the PEAR::Error object.

I which there WAS one true way in this regard. The custom error handlers route is probably the most flexible in this situation. Exceptions are a great idea though if you're either only using your own code, or using libraries that use them.

Unfortunately in the PHP world we're still suffering from the refusal to die of PHP4, so things like exceptions, while they may represent best practise have been incredibly slow to catch on while everyone is still writing things to be able to work in both 4 and 5. Hopefully this debacle is now ending, though by the time it does, we'll have tensions between 6 and 5 instead...

/me holds head in hands...

Answer 2

The idea of exception is elegant and makes the error handling process so smooth. but this only applies when you have appropriate exception classes and in team development, one more important thing is "standard" exceptions. so if you plan to use exceptions, you'd better first standardize your exception types, or the better choice is to use exceptions from some popular framework. one other thing that applies to PHP (where you can write your code object orienter combined with structural code), is that if you are writing your whole application using classes. If you are writing object oriented, then exceptions are better for sure. after all I think your error handling process will be much smoother with exception than trigger_error and stuff.

Answer 3

Obviously, there's no "One Right Way", but there's a multitude of opinions on this one. ;)

Personally i use trigger_error for things the exceptions cannot do, namely notices and warnings (i.e. stuff you want to get logged, but not stop the flow of the application in the same way that errors/exceptions do (even if you catch them at some level)).

I also mostly use exceptions for conditions that are assumed to be non-recoverable (to the caller of the method in which the exception occurs), i.e. serious errors. I don't use exceptions as an alternative to returning a value with the same meaning, if that's possible in a non-convoluted way. For example, if I create a lookup method, I usually return a null value if it didn't find whatever it was looking for instead of throwing an EntityNotFoundException (or equivalent).

So my rule of thumb is this:

• As long as not finding something is a reasonable result, I find it much easier returning and checking for null-values (or some other default value) than handling it using a try-catch-clause.
• If, on the other hand, not finding it is a serious error that's not within the scope of the caller to recover from, I'd still throw an exception.

The reason for throwing exceptions in the latter case (as opposed to triggering errors), is that exceptions are much more expressive, given that you use properly named Exception subclasses. I find that using PHP's Standard Library's exceptions is a good starting point when deciding what exceptions to use: http://www.php.net/~helly/php/ext/spl/classException.html

You might want to extend them to get more semantically correct exceptions for your particular case, however.

Answer 4

The Exceptions are the modern and robust way of signaling an error condition / an exceptional situation. Use them :)

Answer 5

You should use exceptions in "Exceptional circumstances", that is when you call a method doFoo() you should expect it to perform, if for some reason doFoo is unable to do it's job then it should raise an exception.

A lot of old php code would take the approach of returning false or null when a failure has occured, but this makes things hard to debug, exceptions make this debugging much easier.

For example say you had a method called getDogFood() which returned an array of DogFood objects, if you called this method and it returns null when something goes wrong how will your calling code be able to tell whether null was returned because there was an error or there is just no dog food available?

Regarding dealing with legacy code libraries that use php's inbuilt error logging, you can override the error logging with the set_error_handler() function, which you could use to then rethrow a generic Exception.

Now that you have all of your code throwing detailed exceptions, you are free to decide what to do with them, in some parts of your code you may wish to catch them and try alternative methods or you can log them using your own logging functions which might log to a database, file, email - whichever you prefer. In short - Exceptions are more flexible .

Answer 6

If you want to use exceptions instead of errors for your entire application, you can do it with ErrorException and a custom error handler (see the ErrorException page for a sample error handler). The only downside to this method is that non-fatal errors will still throw exceptions, which are always fatal unless caught. Basically, even an E_NOTICE will halt your entire application if your error_reporting settings do not suppress them.

In my opinion, there are several benefits to using ErrorException:

1. A custom exception handler will let you display nice messages, even for errors, using set_exception_handler.
2. It does not disrupt existing code in any way... trigger_error and other error functions will still work normally.
3. It makes it really hard to ignore stupid coding mistakes that trigger E_NOTICEs and E_WARNINGs.

4. You can use try/catch to wrap code that may generate a PHP error (not just exceptions), which is a nice way to avoid using the @ error suppression hack:

   try {
       $foo = $_GET['foo'];
   } catch (ErrorException $e) {
       $foo = NULL;
   }
   

5. You can wrap your entire script in a single try/catch block if you want to display a friendly message to your users when any uncaught error happens. (Do this carefully, because only uncaught errors and exceptions are logged.)