Php/docs/language.exceptions.extending
Extending Exceptions
A User defined Exception class can be defined by extending the built-in Exception class. The members and properties below, show what is accessible within the child class that derives from the built-in Exception class.
Example #1 The Built in Exception class
<?phpclass Exception extends Throwable{ protected $message = 'Unknown exception'; // exception message private $string; // __toString cache protected $code = 0; // user defined exception code protected $file; // source filename of exception protected $line; // source line of exception private $trace; // backtrace private $previous; // previous exception if nested exception public function __construct($message = null, $code = 0, Exception $previous = null); final private function __clone(); // Inhibits cloning of exceptions. final public function getMessage(); // message of exception final public function getCode(); // code of exception final public function getFile(); // source filename final public function getLine(); // source line final public function getTrace(); // an array of the backtrace() final public function getPrevious(); // previous exception final public function getTraceAsString(); // formatted string of trace // Overrideable public function __toString(); // formatted string for display}?>
If a class extends the built-in Exception class and re-defines the constructor, it is highly recommended that it also call parent::__construct() to ensure all available data has been properly assigned. The __toString() method can be overridden to provide a custom output when the object is presented as a string.
Note:
Exceptions cannot be cloned. Attempting to clone an Exception will result in a fatal
E_ERRORerror.
Example #2 Extending the Exception class
<?php/** * Define a custom exception class */class MyException extends Exception{ // Redefine the exception so message isn't optional public function __construct($message, $code = 0, Exception $previous = null) { // some code // make sure everything is assigned properly parent::__construct($message, $code, $previous); } // custom string representation of object public function __toString() { return __CLASS__ . ": [{$this->code}]: {$this->message}\n"; } public function customFunction() { echo "A custom function for this type of exception\n"; }}/** * Create a class to test the exception */class TestException{ public $var; const THROW_NONE = 0; const THROW_CUSTOM = 1; const THROW_DEFAULT = 2; function __construct($avalue = self::THROW_NONE) { switch ($avalue) { case self::THROW_CUSTOM: // throw custom exception throw new MyException('1 is an invalid parameter', 5); break; case self::THROW_DEFAULT: // throw default one. throw new Exception('2 is not allowed as a parameter', 6); break; default: // No exception, object will be created. $this->var = $avalue; break; } }}// Example 1try { $o = new TestException(TestException::THROW_CUSTOM);} catch (MyException $e) { // Will be caught echo "Caught my exception\n", $e; $e->customFunction();} catch (Exception $e) { // Skipped echo "Caught Default Exception\n", $e;}// Continue executionvar_dump($o); // Nullecho "\n\n";// Example 2try { $o = new TestException(TestException::THROW_DEFAULT);} catch (MyException $e) { // Doesn't match this type echo "Caught my exception\n", $e; $e->customFunction();} catch (Exception $e) { // Will be caught echo "Caught Default Exception\n", $e;}// Continue executionvar_dump($o); // Nullecho "\n\n";// Example 3try { $o = new TestException(TestException::THROW_CUSTOM);} catch (Exception $e) { // Will be caught echo "Default Exception caught\n", $e;}// Continue executionvar_dump($o); // Nullecho "\n\n";// Example 4try { $o = new TestException();} catch (Exception $e) { // Skipped, no exception echo "Default Exception caught\n", $e;}// Continue executionvar_dump($o); // TestExceptionecho "\n\n";?>
