Exceptions are used to change the normal flow of a script if a specified error occurs
With PHP 5 came a new object oriented way of dealing with errors.
Exception handling is used to change the normal flow of the code execution if a specified error
(exceptional) condition occurs. This condition is called an exception.This is what
normally happens when an exception is triggered:
We will show different error handling methods:
Note: Exceptions should only be used with error conditions, and should not be used to jump
to another place in the code at a specified point.
When an exception is thrown, the code following it will not be executed, and PHP will try to find
the matching "catch" block.
If an exception is not caught, a fatal error will be issued with an "Uncaught Exception"
Lets try to throw an exception without catching it:
The code above will get an error like this:
To avoid the error from the example above, we need to create the proper code to handle an
Proper exception code should include:
Lets try to trigger an exception with valid code:
The code above throws an exception and catches it:
However, one way to get around the "every throw must have a catch" rule is to set a top
level exception handler to handle errors that slip through.
Creating a custom exception handler is quite simple. We simply create a special class with
functions that can be called when an exception occurs in PHP. The class must be an extension of
the exception class.
The custom exception class inherits the properties from PHP's exception class and you can add
custom functions to it.
Lets create an exception class:
The new class is a copy of the old exception class with an addition of the errorMessage()
function. Since it is a copy of the old class, and it inherits the properties and methods from
the old class, we can use the exception class methods like getLine() and getFile() and
The code above throws an exception and catches it with a custom exception class:
It is possible for a script to use multiple exceptions to check for multiple conditions.
It is possible to use several if..else blocks, a switch, or nest multiple exceptions. These
exceptions can use different exception classes and return different error messages:
The code above tests two conditions and throws an exception if any of the conditions are not
If there was no customException catch, only the base exception catch, the exception would be
Sometimes, when an exception is thrown, you may wish to handle it differently than the standard
way. It is possible to throw an exception a second time within a "catch" block.
A script should hide system errors from users. System errors may be important for the coder, but
is of no interest to the user. To make things easier for the user you can re-throw the exception
with a user friendly message:
The code above tests if the email-address contains the string "example" in it, if it
does, the exception is re-thrown:
If the exception is not caught in its current "try" block, it will search for a catch block on
The set_exception_handler() function sets a user-defined function to handle all uncaught
The output of the code above should be something like this:
In the code above there was no "catch" block. Instead, the top level exception handler
triggered. This function should be used to catch uncaught exceptions.
A simple rule: If you throw something, you have to catch it.
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