Exceptions
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 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 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 #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: ', $e->getMessage(), "\n";
}
// Continue execution
echo "Hello World\n";
?>
The above example will output:
0.2
Caught exception: Division by zero.
Hello World
Example #3 Exception handling with a finally
block
<?php
function inverse($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:
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:
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:
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();
}
?>