PHP has an exception model similar to that of other programming
languages. An exception can be thrown, and caught ("catched") 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 instanceof Throwable .
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 thrown (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.
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.
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 #1 Converting error reporting to exceptions
<?php
function exceptions_error_handler($severity, $message, $filename, $lineno) {
throw new ErrorException($message, 0, $severity, $filename, $lineno);
}
set_error_handler('exceptions_error_handler');
?>
The Standard PHP Library (SPL) provides a good number of built-in exceptions.
Example #2 Throwing an Exception
<?php
function inverse($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: ', $e->getMessage(), "\n";
}
// Continue execution
echo "Hello World\n";
?>The above example will output:
0.2 Caught exception: Division by zero. Hello World
Example #3 Exception handling with a finally block
<?php
function inverse($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 #4 Interaction between the finally block and return
<?php
function test() {
try {
throw new Exception('foo');
} catch (Exception $e) {
return 'catch';
} finally {
return 'finally';
}
}
echo test();
?>The above example will output:
finally
Example #5 Nested Exception
<?php
class 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:
string(4) "foo!"
Example #6 Multi catch exception handling
<?php
class 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:
string(11) "MyException"
Example #7 Omitting the caught variable
Only permitted in PHP 8.0.0 and later.
<?php
class 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.";
}
?>The above example will output:
A SpecificException was thrown, but we don't care about the details.
Example #8 Throw as an expression
Only permitted in PHP 8.0.0 and later.
<?php
function test() {
do_something_risky() or throw new Exception('It did not work');
}
function do_something_risky() {
return false; // Simulate failure
}
try {
test();
} catch (Exception $e) {
print $e->getMessage();
}
?>The above example will output:
It did not work
If you intend on creating a lot of custom exceptions, you may find this code useful. I've created an interface and an abstract exception class that ensures that all parts of the built-in Exception class are preserved in child classes. It also properly pushes all information back to the parent constructor ensuring that nothing is lost. This allows you to quickly create new exceptions on the fly. It also overrides the default __toString method with a more thorough one.
<?php
interface IException
{
/* Protected methods inherited from Exception class */
public function getMessage(); // Exception message
public function getCode(); // User-defined Exception code
public function getFile(); // Source filename
public function getLine(); // Source line
public function getTrace(); // An array of the backtrace()
public function getTraceAsString(); // Formated string of trace
/* Overrideable methods inherited from Exception class */
public function __toString(); // formated string for display
public function __construct($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 $trace; // Unknown
public function __construct($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}Easy to understand `finally`.
<?php
try {
try {
echo "before\n";
1 / 0;
echo "after\n";
} finally {
echo "finally\n";
}
} catch (\Throwable) {
echo "exception\n";
}
?>
# Print:
before
finally
exceptionCustom 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());
}
?>As noted elsewhere, throwing an exception from the `finally` block will replace a previously thrown exception. But the original exception is magically available from the new exception's `getPrevious()`.
<?php
try {
try {
throw new RuntimeException('Exception A');
} finally {
throw new RuntimeException('Exception B');
}
}
catch (Throwable $exception) {
echo $exception->getMessage(), "\n";
// 'previous' is magically available!
echo $exception->getPrevious()->getMessage(), "\n";
}
?>
Will print:
Exception B
Exception AThe "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 $e->getMessage()." catch out\n";
}
?>
The output is:
Hello catch in
Hello finally
Bye catch out‘Normal execution (when no exception is thrown within the try block, *or when a catch matching the thrown exception’s class is not present*) will continue after that last catch block defined in sequence.’
‘If an exception is not caught, a PHP Fatal Error will be issued with an "Uncaught Exception ..." message, unless a handler has been defined with set_exception_handler().’
These two sentences seem a bit contradicting about what happens ‘when a catch matching the thrown exception’s class is not present’ (and the second sentence is actually correct).In case your E_WARNING type of errors aren't catchable with try/catch you can change them to another type of error like this:
<?php
set_error_handler(function($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();
}
?>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:
<?php
try {
throw new Error( "foobar" );
// or:
// throw new Exception( "foobar" );
}
catch (Throwable $e) {
var_export( $e );
}
?>#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.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
?><?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 !"Contrary to the documentation it is possible in PHP 5.5 and higher use only try-finally blocks without any catch block.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 name
try
{
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/>";
}
?>