Exceptions

    Indice dei contenuti

    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.

    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.

    Note

    Nota:

    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');
    ?>

    Suggerimento

    The Standard PHP Library (SPL) provides a good number of built-in exceptions.

    Esempi

    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";
    ?>

    Il precedente esempio visualizzerà:

    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";
    ?>

    Il precedente esempio visualizzerà:

    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();
    ?>

    Il precedente esempio visualizzerà:

    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();

    ?>

    Il precedente esempio visualizzerà:

    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();

    ?>

    Il precedente esempio visualizzerà:

    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.";
    }
    ?>

    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');
    }

    try {
    test();
    } catch (    Exception $e) {
    print     $e->getMessage();
    }
    ?>

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    User Contributed Notes 13 notes

    up
    122
    ask at nilpo dot com
    15 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; // 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}
    up
    78
    Johan
    13 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());
    }
    ?>
    up
    9
    tianyiw at vip dot qq dot com
    10 months ago
    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
    exception
    up
    4
    jlherren
    5 months ago
    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 A
    up
    17
    daviddlowe dot flimm at gmail dot com
    6 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:

    <?php

    try {
    throw new     Error( "foobar" );
    // or:
    // throw new Exception( "foobar" );
    }
    catch (    Throwable $e) {
    var_export( $e );
    }

    ?>
    up
    25
    Shot (Piotr Szotkowski)
    15 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).
    up
    15
    christof+php[AT]insypro.com
    7 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();
    }
    ?>
    up
    24
    Edu
    11 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
    up
    11
    mlaopane at gmail dot com
    6 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 !"
    up
    14
    Simo
    9 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.
    up
    15
    telefoontoestel at nospam dot org
    10 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
    ?>
    up
    8
    Tom Polomsk
    9 years ago
    Contrary to the documentation it is possible in PHP 5.5 and higher use only try-finally blocks without any catch block.
    up
    7
    Sawsan
    12 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 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/>";
    }

    ?>
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