set_error_handler
Thanks to mastabog we know that throwing an exception within the exception handler will trigger a fatal error and a debugging nightmare. To avoid throwing an exception within there should be easy.
However, if you use a custom error handler to convert errors to ErrorExceptions suddenly there are a multitude of new ways to accidentally throw exceptions within the exception handler.
<?php
function error_handler($code, $message, $file, $line)
{
if (0 == error_reporting())
{
return;
}
throw new ErrorException($message, 0, $code, $file, $line);
}
function exception_handler($e)
{
// ... normal exception stuff goes here
print $undefined; // This is the underlying problem
}
set_error_handler("error_handler");
set_exception_handler("exception_handler");
throw new Exception("Just invoking the exception handler");
?>
Output: Fatal error: Exception thrown without a stack frame in Unknown on line 0
The best way I have found to avoid this is to wrap up everything in the exception handler in a try/catch block.
<?php
function exception_handler($e)
{
try
{
// ... normal exception stuff goes here
print $undefined; // This is the underlying problem
}
catch (Exception $e)
{
print get_class($e)." thrown within the exception handler. Message: ".$e->getMessage()." on line ".$e->getLine();
}
}
?>
Output: ErrorException thrown within the exception handler. Message: Undefined variable: undefined on line 14
This speeds up debugging and offers some scalability to any other exceptions accidentally thrown within the exception handler.
Another solution is to restore the error handler at the beginning of the exception handler. While this is a silver bullet in terms of avoiding the ErrorExceptions, debugging messages then rely on the error_reporting() level and the display_errors directive. Why mention this? It might be preferable for production code since we care more about hiding errors from users than convenient debugging messages.
set_exception_handler
(PHP 5)
set_exception_handler — Sets a user-defined exception handler function
Description
Sets the default exception handler if an exception is not caught within a try/catch block. Execution will stop after the exception_handler is called.
Parameters
- exception_handler
-
Name of the function to be called when an uncaught exception occurs. This function must be defined before calling set_exception_handler(). This handler function needs to accept one parameter, which will be the exception object that was thrown.
Return Values
Returns the name of the previously defined exception handler, or NULL on error. If no previous handler was defined, NULL is also returned.
Examples
Example #1 set_exception_handler() example
<?php
function exception_handler($exception) {
echo "Uncaught exception: " , $exception->getMessage(), "\n";
}
set_exception_handler('exception_handler');
throw new Exception('Uncaught Exception');
echo "Not Executed\n";
?>
See Also
- restore_exception_handler() - Restores the previously defined exception handler function
- restore_error_handler() - Restores the previous error handler function
- error_reporting() - Sets which PHP errors are reported
- information about the callback type
- PHP 5 Exceptions
add a note
User Contributed Notesset_exception_handler
joshua dot boyle-petrie at its dot monash dot edu
09-Jan-2009 07:44
09-Jan-2009 07:44
marques at displague dot com
14-Apr-2008 02:19
14-Apr-2008 02:19
frank,
Your exception handler is configured to be the handler for all exceptions, yet if a basic 'Exception' is thrown, your static method will error because 'Exception's do not have 'getException'. Because of this I don't see a real purpose to making the uncaught handler a class that extends Exception.
I do like the idea of using static methods of a general Exception handling class.
<?php
class ExceptionHandler {
public static function printException(Exception $e)
{
print 'Uncaught '.get_class($e).', code: ' . $e->getCode() . "<br />Message: " . htmlentities($e->getMessage())."\n";
}
public static function handleException(Exception $e)
{
self::printException($e);
}
}
set_exception_handler(array("ExceptionHandler", "handleException"));
class NewException extends Exception {}
try {
throw new NewException("Catch me once", 1);
} catch (Exception $e) {
ExceptionHandler::handleException($e);
}
throw new Exception("Catch me twice", 2);
?>
Gives:
Uncaught NewException, code: 1<br />Message: Catch me once
Uncaught Exception, code: 2<br />Message: Catch me twice
There are much more interesting things that can be done like reformating and optionally displaying or emailing them. But this class acts a nice container for those functions.
frank at netventures dot com dot au
06-Nov-2007 06:10
06-Nov-2007 06:10
Hey all, i've just started to use the exception suite instead of the normal PHP error suite. For those of you looking for an object orientated way to do this without looking down at Glen and Sean's examples (Lesson 1: ALWAYS read the logs!), here you go:
<?php
class NewException extends Exception
{
public function __construct($message, $code=NULL)
{
parent::__construct($message, $code);
}
public function __toString()
{
return "Code: " . $this->getCode() . "<br />Message: " . htmlentities($this->getMessage());
}
public function getException()
{
print $this; // This will print the return from the above method __toString()
}
public static function getStaticException($exception)
{
$exception->getException(); // $exception is an instance of this class
}
}
set_exception_handler(array("NewException", "getStaticException"));
throw new NewException("Catch me!!!", 69);
?>
Let me know if i'm missing something obvious as I left my glasses at home and I just came back from the Melbourne cup (If I won then I wouldn't be at work still!).
bhyoram at zahav dot net dot il
11-Jul-2007 04:33
11-Jul-2007 04:33
to do it in command-line, use this :
echo '<?php function ff ($exception) { printf ("I am a handler, got %s\n",$exception->getMessage ()) ;} set_exception_handler ("ff") ; throw new Exception ("blabla") ; echo "This is bad\n" ; | php
parazuce at gmail dot com
09-Jul-2007 10:41
09-Jul-2007 10:41
I've been messing around with this function, and have noticed you can pass an anonymous function (created with create_function()) through as the default handler, for example:
set_exception_handler(create_function('$e', 'exit("An unknown error occurred");'));
That snippet of code can be used if you simply want to suppress all exceptions that are not handled. This can be a great thing, because secure data could possibly be leaked otherwise (for example, the default exception handler could output a snippet of your SQL code that was involved with the exception being thrown).
You will want to use this wisely, however (if at all).
reg dot php dot manual at entropy dot ch
09-May-2007 01:59
09-May-2007 01:59
In my experience, the static keyword is crucial for error handlers which are methods of a class instead of free-standing functions.
static function exceptionHandler($exception)
works but
function exceptionHandler($exception)
doesn't and results in a "Fatal error: Exception thrown without a stack frame in Unknown on line 0" message.
"public" is optional as it is the default anyway (but it is probably clearer to write it explicitly).
Glen
03-Mar-2007 08:34
03-Mar-2007 08:34
If you want a class instance to handle the exception, this is how you do it :
<?php
class example {
public function __construct() {
@set_exception_handler(array($this, 'exception_handler'));
throw new Exception('DOH!!');
}
public function exception_handler($exception) {
print "Exception Caught: ". $exception->getMessage() ."\n";
}
}
$example = new example;
?>
See the first post (Sean's) for a static example. As Sean points out, the exception_handler function must be declared public.
mastabog at hotmail dot com
08-Aug-2006 02:44
08-Aug-2006 02:44
A behaviour not documented or discussed enough, yet pretty common is that is that if an exception is thrown from the global exception handler then a fatal error occurs (Exception thrown without a stack frame). That is, if you define your own global exception handler by calling set_exception_handler() and you throw an exception from inside it then this fatal error occurs. It is only natural though, as the callback defined by set_exception_handler() is only called on uncaught (unhandled) exceptions so if you throw one from there then you get this fatal error as there is no exception handler left (you override the php internal one by calling set_exception_handler()), hence no stack frame for it.
Example:
<?php
function myExceptionHandler (Exception $ex)
{
throw $ex;
}
set_exception_handler("myExceptionHandler");
throw new Exception("This should cause a fatal error and this message will be lost");
?>
Will cause a Fatal error: Exception thrown without a stack frame
If you skip/comment the set_exception_handler("...") line then the internal PHP global handler will catch the exception and output the exception message and trace (as string) to the browser, allowing you to at least see the exception message.
While it is a very good idea to always define your own global exception handler by using the set_exception_handler() function, you should pay attention and never throw an exception from it (or if you do then catch it).
Finally, every serious coder should use an IDE with debugging capabilities. Tracking down an error like this becomes a trivial matter by using simple debugging "Step into" commands (I for one recommend Zend IDE v5.2 at the moment of this writing). I have seen numerous messages on the internet with people wondering why this message pops up.
Cheers
p.s. Other causes for this error which are somehow unrelated to this is when you throw an exception from a destructor (the reasons behind that are similar though, the global handler might no longer exist due to the php engine shutting the page down).
mc-php-doco at oak dot homeunix dot org
07-Apr-2006 04:41
07-Apr-2006 04:41
This seems not to work when calling the PHP binary with the '-r' flag.
For example, if I run it like this:
php -r '
function exception_handler($exception) {
echo "Uncaught exception: " , $exception->getMessage(), "\n";
}
set_exception_handler("exception_handler");
throw new Exception("Uncaught Exception");
echo "Not Executed\n";
'
Or if I place it in a file and run it like this:
php -r 'include "./tmp.php";'
I get a stack trace instead of having the function 'exception_handler' called. If run it like this:
php tmp.php
It works fine.
(Why run code from '-r'? Sometimes it's useful to add stuff around the include like calls to microtime for benchmarks, or to include a library and then call a few functions from the library, all in an ad-hoc way without having to create new files.)
PHP versions 5.1.2 and 5.0.4.
ch at westend dot com
21-Feb-2006 03:06
21-Feb-2006 03:06
It seems that although the Exception contains a backtrace itself, the stack for the debug_backtrace() function is empty when entering an exception handler. This is very inconvinient. See bug #36477.
sean at seanodonnell dot com
23-Oct-2005 11:48
23-Oct-2005 11:48
Using the 'set_exception_handler' function within a class, the defined 'exception_handler' method must be declared as 'public' (preferrable 'public static' if you use the "array('example', 'exception_handler')" syntax).
<?php
class example {
public function __construct() {
@set_exception_handler(array('example', 'exception_handler'));
throw new Exception('DOH!!');
}
public static function exception_handler($exception) {
print "Exception Caught: ". $exception->getMessage() ."\n";
}
}
$example = new example;
echo "Not Executed\n";
?>
Declaring the 'exception_handler' function as 'private' causes a FATAL ERROR.
[derick: red. updated statement about static a bit]