PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

196 Chapter 7 Error and Exception Handling
You can see that we used the first four of these methods in Listing 7.1.You could obtain
the same information (plus the backtrace) by executing
echo $e;
A backtrace shows which functions were executing at the time the exception was raised.
User-Defined Exceptions
Instead of instantiating and passing an instance of the base Exception class, you can pass
any other object you like. In most cases, you will extend the Exception class to create
your own exception classes.
You can pass any other object with your throw clause.You may occasionally want to
do this if you are having problems with one particular object and want to pass it through
for debugging purposes.
Most of the time, however, you will extend the base Exception class.The PHP manual
provides code that shows the skeleton of the Exception class.This code, taken from
http://us.php.net/manual/en/language.oop5.php, is reproduced in Listing 7.2. Note that
this is not the actual code but represents what you can expect to inherit.
Listing 7.2
Exception class—This Is What You Can Expect to Inherit