Table of Contents
PHP has an exception model similar to that of other programming languages. An exception can be throw
n, and caught
("catch
ed") within PHP. Code may be surrounded in a try
block, to facilitate the catching of potential exceptions. Each try
must have at least one corresponding
catch
or finally
block.
If an exception is thrown and its current function scope has no catch
block, the exception will "bubble up" the call stack to the
calling function until it finds a matching catch
block. All finally
blocks it encounters along the way will be executed. If the call stack is unwound all the way to the global scope without encountering a matching
catch
block, the program will terminate with a fatal error unless a global exception handler has been set.
The thrown object must be an instance of the Exception class or a subclass of
Exception. Trying to throw an object that is not will result in a PHP Fatal Error.
As of PHP 8.0.0, the throw
keyword is an expression and may be used in any expression context. In prior versions it was a statement and was required to be on its own line.
catch
A catch
block defines how to respond to a thrown exception. A catch
block defines one or more types of exception or error it can handle, and optionally a variable to which to assign the exception. (The variable was required prior to PHP 8.0.0.) The first
catch
block a thrown exception or error encounters that matches the type of the thrown object will handle the object.
Multiple catch
blocks can be used to catch different classes of exceptions. Normal execution (when no exception is thrown within the
try
block) will continue after that last catch
block defined in sequence. Exceptions can be throw
n (or re-thrown) within a
catch
block. If not, execution will continue after the catch
block that was triggered.
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 a handler has been defined with set_exception_handler().
As of PHP 7.1.0, a
catch
block may specify multiple exceptions using the pipe (|
) character. This is useful for when different exceptions from different class hierarchies are handled the same.
As of PHP 8.0.0, the variable name for a caught exception is optional. If not specified, the
catch
block will still execute but will not have access to the thrown object.
finally
A finally
block may also be specified after or instead of
catch
blocks. Code within the finally
block will always be executed after the try
and
catch
blocks, regardless of whether an exception has been thrown, and before normal execution resumes.
One notable interaction is between the finally
block and a return
statement. If a
return
statement is encountered inside either the try
or the catch
blocks, the finally
block will still
be executed. Moreover, the return
statement is evaluated when encountered, but the result will be returned after the finally
block is executed. Additionally, if the finally
block also contains
a return
statement, the value from the finally
block is returned.
Global exception handler
If an exception is allowed to bubble up to the global scope, it may be caught by a global exception handler if set. The
set_exception_handler() function can set a function that will be called in place of a catch
block if no other block is invoked. The effect is essentially the same as if the entire program were wrapped in a
try
-catch
block with that function as the catch
.
Notes
Note:
Internal PHP functions mainly
use Error reporting, only modern Object-oriented extensions use exceptions. However, errors can be easily translated to exceptions with ErrorException. This technique only works with non-fatal errors, however.
Example #3 Converting error reporting to exceptions
<?php
function exceptions_error_handler($severity, $message, $filename, $lineno) {
throw new ErrorException($message, 0, $severity, $filename, $lineno);
}set_error_handler('exceptions_error_handler');
?>
Examples
Example #4 Throwing an Exception
<?php
function inverse($x) {
if (!$x) {
throw new Exception('Division by zero.');
}
return 1/$x;
}
try {
echo
inverse(5) . "\n";
echo inverse(0) . "\n";
} catch (Exception $e) {
echo 'Caught exception: ', $e->getMessage(), "\n";
}// Continue execution
echo "Hello World\n";
?>
The above example will output:
0.2
Caught exception: Division by zero.
Hello World
Example #5 Exception handling with a
finally
block
<?php
function inverse($x) {
if (!$x) {
throw new Exception('Division by zero.');
}
return 1/$x;
}
try {
echo
inverse(5) . "\n";
} catch (Exception $e) {
echo 'Caught exception: ', $e->getMessage(), "\n";
} finally {
echo "First finally.\n";
}try {
echo
inverse(0) . "\n";
} catch (Exception $e) {
echo 'Caught exception: ', $e->getMessage(), "\n";
} finally {
echo "Second finally.\n";
}// Continue execution
echo "Hello World\n";
?>
The above example will output:
0.2
First finally.
Caught exception: Division by zero.
Second finally.
Hello World
Example #6 Interaction between the finally
block and
return
<?phpfunction test() {
try {
throw new Exception('foo');
} catch (Exception $e) {
return 'catch';
} finally {
return 'finally';
}
}
echo
test();
?>
The above example will output:
Example #7 Nested Exception
<?phpclass MyException extends Exception { }
class
Test {
public function testing() {
try {
try {
throw new MyException('foo!');
} catch (MyException $e) {
// rethrow it
throw $e;
}
} catch (Exception $e) {
var_dump($e->getMessage());
}
}
}$foo = new Test;
$foo->testing();?>
The above example will output:
Example #8 Multi catch exception handling
<?phpclass MyException extends Exception { }
class
MyOtherException extends Exception { }class
Test {
public function testing() {
try {
throw new MyException();
} catch (MyException | MyOtherException $e) {
var_dump(get_class($e));
}
}
}$foo = new Test;
$foo->testing();?>
The above example will output:
Example
#9 Omitting the caught variable
Only permitted in PHP 8.0.0 and later.
<?phpclass SpecificException extends Exception {}
function
test() {
throw new SpecificException('Oopsie');
}try {
test();
} catch (SpecificException) {
print "A SpecificException was thrown, but we don't care about the details.";
}
?>
Example #10 Throw as an expression
Only permitted in PHP 8.0.0 and later.
<?phpclass SpecificException extends Exception {}
function
test() {
do_something_risky() or throw new Exception('It did not work');
}try {
test();
} catch (Exception $e) {
print $e->getMessage();
}
?>
ask at nilpo dot
com ¶
13 years ago
If you intend on creating a lot of custom exceptions, you may find this code useful. I've created an interface and an abstract exception class that ensures that all parts of the built-in Exception class are preserved in child classes. It also properly pushes all information back to the parent constructor ensuring that nothing is lost. This allows you to quickly create new exceptions on the fly. It also overrides the default __toString method with a more thorough one.
<?php
interface IException
{
/* Protected methods inherited from Exception class */
public function getMessage(); // Exception message
public function getCode(); // User-defined Exception code
public function getFile(); // Source filename
public function getLine(); // Source line
public function getTrace(); // An array of the backtrace()
public function getTraceAsString(); // Formated string of trace
/* Overrideable methods inherited from Exception class */
public function __toString(); // formated string for display
public function __construct($message = null, $code = 0);
}abstract class
CustomException extends Exception implements IException
{
protected $message = 'Unknown exception'; // Exception message
private $string; // Unknown
protected $code = 0; // User-defined exception code
protected $file; // Source filename of exception
protected $line; // Source line of exception
private $trace; // Unknownpublic function __construct($message = null, $code = 0)
{
if (!$message) {
throw new $this('Unknown '. get_class($this));
}
parent::__construct($message, $code);
} public function
__toString()
{
return get_class($this) . " '{$this->message}' in {$this->file}({$this->line})\n"
. "{$this->getTraceAsString()}";
}
}
?>
Now you can create new exceptions in one line:<?php
class TestException extends CustomException {}
?>
Here's a test that shows that all information is properly preserved throughout the backtrace.
<?php
function exceptionTest()
{
try {
throw new TestException();
}
catch (TestException $e) {
echo "Caught TestException ('{$e->getMessage()}')\n{$e}\n";
}
catch (Exception $e) {
echo "Caught Exception ('{$e->getMessage()}')\n{$e}\n";
}
}
echo
'<pre>' . exceptionTest() . '</pre>';
?>
Here's a sample output:Caught TestException ('Unknown TestException')
TestException 'Unknown TestException' in C:\xampp\htdocs\CustomException\CustomException.php(31)
#0 C:\xampp\htdocs\CustomException\ExceptionTest.php(19): CustomException->__construct()
#1 C:\xampp\htdocs\CustomException\ExceptionTest.php(43): exceptionTest()
#2 {main}
Johan ¶
11 years ago
Custom error handling on entire pages can avoid half rendered pages for the users:
<?php
ob_start();
try {
/*contains all page logic
and throws error if needed*/
...
} catch (Exception $e) {
ob_end_clean();
displayErrorPage($e->getMessage());
}
?>
christof+php[AT]insypro.com ¶
5 years ago
In case your E_WARNING type of errors aren't catchable with try/catch you can change them to another type of error like this:
<?php
set_error_handler(function($errno, $errstr, $errfile, $errline){
if($errno === E_WARNING){
// make it more serious than a warning so it can be caught
trigger_error($errstr, E_ERROR);
return true;
} else {
// fallback to default php error handler
return false;
}
});
try {
// code that might result in a E_WARNING
} catch(Exception $e){
// code to handle the E_WARNING (it's actually changed to E_ERROR at this point)
} finally {
restore_error_handler();
}
?>
Shot (Piotr
Szotkowski) ¶
13 years ago
‘Normal execution (when no exception is thrown within the try block, *or when a catch matching the thrown exception’s class is not present*) will continue after that last catch block defined in sequence.’
‘If an exception is not caught, a PHP Fatal Error will be issued with an “Uncaught Exception …” message, unless a handler has been defined with set_exception_handler().’
These two sentences seem a bit contradicting about what happens ‘when a catch matching the thrown exception’s class is not present’ (and the second sentence is actually correct).
Simo ¶
7 years ago
#3 is not a good example. inverse("0a") would not be caught since (bool) "0a" returns true, yet 1/"0a" casts the string to integer zero and attempts to perform the calculation.
Edu ¶
9 years ago
The "finally" block can change the exception that has been throw by the catch block.
<?php
try{
try {
throw new \Exception("Hello");
} catch(\Exception $e) {
echo $e->getMessage()." catch in\n";
throw $e;
} finally {
echo $e->getMessage()." finally \n";
throw new \Exception("Bye");
}
} catch (\Exception $e) {
echo $e->getMessage()." catch out\n";
}
?>
The output is:
Hello catch in
Hello finally
Bye catch out
mlaopane at
gmail dot com ¶
4 years ago
<?php/**
* You can catch exceptions thrown in a deep level function
*/function employee()
{
throw new \Exception("I am just an employee !");
}
function
manager()
{
employee();
}function
boss()
{
try {
manager();
} catch (\Exception $e) {
echo $e->getMessage();
}
}boss(); // output: "I am just an employee !"
daviddlowe dot flimm at gmail dot com ¶
5
years ago
Starting in PHP 7, the classes Exception and Error both implement the Throwable interface. This means, if you want to catch both Error instances and Exception instances, you should catch Throwable objects, like this:
<?phptry {
throw new Error( "foobar" );
// or:
// throw new Exception( "foobar" );
}
catch (Throwable $e) {
var_export( $e );
}?>
telefoontoestel at nospam dot org ¶
8 years ago
When using finally keep in mind that when a exit/die statement is used in the catch block it will NOT go through the finally block.
<?php
try {
echo "try block<br />";
throw new Exception("test");
} catch (Exception $ex) {
echo "catch block<br />";
} finally {
echo "finally block<br />";
}// try block
// catch block
// finally block
?>
<?php
try {
echo "try block<br />";
throw new Exception("test");
} catch (Exception $ex) {
echo "catch block<br />";
exit(1);
} finally {
echo "finally block<br />";
}// try block
// catch block
?>
Tom Polomsk ¶
7 years ago
Contrary to the documentation it is possible in PHP 5.5 and higher use only try-finally blocks without any catch block.
Sawsan ¶
10 years ago
the following is an example of a re-thrown exception and the using of getPrevious function:
<?php
$name
= "Name";//check if the name contains only letters, and does not contain the word nametry
{
try
{
if (preg_match('/[^a-z]/i', $name))
{
throw new Exception("$name contains character other than a-z A-Z");
}
if(strpos(strtolower($name), 'name') !== FALSE)
{
throw new Exception("$name contains the word name");
}
echo "The Name is valid";
}
catch(Exception $e)
{
throw new Exception("insert name again",0,$e);
}
} catch (
Exception $e)
{
if ($e->getPrevious())
{
echo "The Previous Exception is: ".$e->getPrevious()->getMessage()."<br/>";
}
echo "The Exception is: ".$e->getMessage()."<br/>";
}?>
Daan ¶
1 year ago
I would like to emphasise that you can not rethrow an Exception inside a catch-block and expect that the next catch-block will handle it.
<?php try {
throw new RuntimeException('error');
} catch (RuntimeException $e) {
throw $e;
} catch (Exception $e) {
// this will not be executed[
}
?>
The primary method of handling exceptions in PHP is the try-catch. In a nutshell, the try-catch is a code block that can be used to deal with thrown exceptions without interrupting program execution. In other words, you can "try" to execute a block of code, and "catch" any PHP exceptions that are thrown.
PHP supports using multiple catch blocks within try catch. This allows us to customize our code based on the type of exception that was thrown. This is useful for customizing how you display an error message to a user, or if you should potentially retry something that failed the first time.