PHP 5 has an exception model similar to that of other programming languages.
An exception can be thrown, try and caught within PHP. A Try block must
include at least one catch block. Multiple catch blocks can be used to
catch different classtypes; execution will continue after that last catch
block defined in sequence. Exceptions can be thrown within catch blocks.
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 message, unless there has been a handler defined with
set_exception_handler().
Example 18-22. Throwing an Exception
<?php
try {
$error = 'Always throw this error';
throw new Exception($error);
// code following an exception isn't executed.
echo 'Never executed';
}
catch (Exception $e) {
echo "Caught exception: ", $e, "\n";
}
/* continue execution */
?>
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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 18-23. The Built in Exception class
<?php
class Exception {
protected $message = 'Unknown exception'; // exception message
protected $code = 0; // user defined exception code
protected $file; // source filename of exception
protected $line; // source line of exception
function __construct(string $message=NULL, int code=0);
final function getMessage(); // message of exception
final function getCode(); // code of exception
final function getFile(); // source filename
final function getTrace(); // an array of the backtrace()
final function getTraceAsString(); // formated string of trace
/* Overrideable */
function _toString(); // formated string for display
}
?>
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If a class extends the built-in Exception class and re-defines the constructor, it is highly recomended
that it also call parent::__construct()
to ensure all available data has been properly assigned. The __toString() method can be overriden
to provide a custom output when the object is presented as a string.
Example 18-24. Extending the Exception class
<?php
class MyException extends Exception {
/* Redefine the exception so message isn't optional */
public function __construct($message, $code = 0) {
// custom stuff you want to do..
// ...
/* make sure everything is assigned properly */
parent::__construct($message, $code);
}
/* custom string representation of object */
public function __toString() {
return __CLASS__ . ": [{$this->code}]: {$this->message}\n";
}
public function customFunction() {
echo "A Custom function for this type of exception\n";
}
}
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 isnt allowed as a parameter', 6);
break;
default:
// No exception, object will be created.
$this->var = $avalue;
break;
}
}
}
$o = null;
try {
$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", $e;
}
var_dump($o); /* continue execution */
echo "\n\n";
try {
$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", $e;
}
var_dump($o); /* continue execution */
echo "\n\n";
try {
$o = new TestException(TestException::THROW_CUSTOM);
}
catch (Exception $e) { /* Will be caught */
echo "Default Exception caught\n", $e;
}
var_dump($o); /* continue execution */
echo "\n\n";
try {
$o = new TestException();
}
catch (Exception $e) { /* skipped, no exception */
echo "Default Exception caught\n", $e;
}
var_dump($o); /* continue execution */
echo "\n\n";
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