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Extending Exceptions

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.

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 #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'); ?>

Examples

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 Worldn"; ?>