Upgrading to PHP 5

System Exceptions

In contrast to some languages, notably Python and Java, PHP 5 doesn’t throw exceptions whenever there’s a problem. In fact, it never throws exceptions when you’re using a procedural function. Instead, exceptions are strictly reserved for objects.

Furthermore, even when you’re using an object, PHP throws exceptions only in two instances:

• Errors in constructors

• “Serious” problems in some extensions

These are the two instances when you must place your code inside a try/catch or risk a fatal error.

Constructors

Whenever there’s an error during object instantiation, PHP throws an exception to signal failure. It must throw an exception because a constructor always returns an object, so it cannot return false or another value to indicate that it couldn’t properly create an object.

You’ve already seen one example of a constructor throwing an exception back in Example 7-3. When you pass DOMElement an illegal tag name, DOMElement throws an exception.

A non-DOM example is the SQLite extension, which issues an exception when you don’t provide a database name:

try {
    $db = new SQLiteDatabase( );
} catch (Exception $e) {
    print $e;
}

exception 'SQLiteException' with message 'SQLiteDatabase::_ _construct( ) expects at least  1 parameter, 0 given' in /www/www.example.com/sqlite.php:2
               Stack trace:
               #0 {main} 

Serious Problems

In PHP 5, extensions throw exceptions only when there’s serious logic error. Other errors are still returned in the traditional manner, by ...