PHP - Exception Handling

PHP 5 has an exception model similar to that of other programming languages. Exceptions are important and provides a better control over error handling.

Lets explain there new keyword related to exceptions.

Try − A function using an exception should be in a "try" block. If the exception does not trigger, the code will continue as normal. However if the exception triggers, an exception is "thrown".

Throw − This is how you trigger an exception. Each "throw" must have at least one "catch".

Catch − A "catch" block retrieves an exception and creates an object containing the exception information.

When an exception is thrown, code following the statement will not be executed, and PHP will attempt to find the first matching catch block. If an exception is not caught, a PHP Fatal Error will be issued with an "Uncaught Exception

An exception can be thrown, and caught ("catched") within PHP. Code may be surrounded in a try block.

Each try must have at least one corresponding catch block. Multiple catch blocks can be used to catch different classes of exceptions.

Exceptions can be thrown (or re-thrown) within a catch block

Example -

<?php try { $error = 'Always throw this error'; throw new Exception($error); // Code following an exception is not executed. echo 'Never executed'; }catch (Exception $e) { echo 'Caught exception: ', $e->getMessage(), "\n"; } // Continue execution echo 'Hello World'; ?>

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Creating Custom Exception Handler

You can define your own custom exception handler. Use following function to set a user-defined exception handler function.

Here exception_handler is the name of the function to be called when an uncaught exception occurs. This function must be defined before calling set_exception_handler().

Example -

<?php function exception_handler($exception) { echo "Uncaught exception: " , $exception->getMessage(), "\n"; } set_exception_handler('exception_handler'); throw new Exception('Uncaught Exception'); echo "Not Executed\n"; ?>

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