The world of exceptions

knowj

I have started to delve more into the world of exceptions and due to the lack of documentation on this topic I wouldn't mind some opinion.

I have extended the standard Exception class just to allow logging of the errors.

Am I going about this in the right way or should I be looking at a different technique?

public function __construct()
{
	$this->db = new database::getInstance();
}

public function gallery($gallery)
{
	try
	{
		//ignore the query it's incomplete
		if (!$stmt = $this->db->prepare("SELECT g.id, g.caption, g.image, g.thumb, gr.title, WHERE g.main='1' AND gr.live='1' AND g.live='1' AND g.delete!='1' AND gr.delete!='1' AND gr.url=? ORDER BY gr.order ASC"))
		{
			throw new mException($this->db->error, $this->db->error_no);
		}

	$stmt->bind_param('s', $gallery);

	if (!$stmt->execute())
	{
		throw new mException($stmt->error, $stmt->error_no);
	}

	$stmt->bind_result($this->id, $this->caption, $this->image, $this->thumb, $this->title);

	while ($stmt->fetch())
	{
		$array[] = $this->objectToArray();
	}
}
catch (mException $e)
{
	$e->errorLog(); // Echo error if in debug mode else save data to flat file or database
}
}

I have also started to put together a replacement for the standard error reporting using the ErrorException class

function exceptionErrorHandler($errno, $errstr, $errfile, $errline )
{
	try
	{
		throw new ErrorException($errstr, 0, $errno, $errfile, $errline);
	}
	catch (ErrorException $e)
	{
		try
		{
			throw new mException($e->message, $e->number);
		}
		catch (mException $m)
		{
			$e->errorLog();
		}
	}
}

The code it's self is the simple thing I have no problem with that technique is the one thing I always question.

All opinion is greatly appreciated.

laserlight

knowj wrote:
I have extended the standard Exception class just to allow logging of the errors.

Am I going about this in the right way or should I be looking at a different technique?

It does not sound wrong, but I am uncomfortable with your demonstrated usage. Typically, an exception is not caught in the same function in which it is thrown. Rather, it is propagated until a point where it can be handled appropriately or translated accordingly.

The way you are using it looks like you would be better off just logging the error at the various points and returning from the function immediately. If you want to throw an exception then you should just let it propagate to the caller, i.e., move the try/catch to the caller, or the caller's caller, etc.

knowj wrote:
I have also started to put together a replacement for the standard error reporting using the ErrorException class

It seems to me that you could simplify it to:

function exceptionErrorHandler($errno, $errstr, $errfile, $errline)
{
    $e = new ErrorException($errstr, 0, $errno, $errfile, $errline);
    $e = new mException($e->message, $e->number);
    $e->errorLog();
}

But this seems to miss the point. You probably want to do this instead:

function exceptionErrorHandler($errno, $errstr, $errfile, $errline)
{
    $e = new ErrorException($errstr, 0, $errno, $errfile, $errline);
    throw new mException($e->message, $e->number);
}

set_error_handler('exceptionErrorHandler');

knowj

laserlight;10942899 wrote:
It does not sound wrong, but I am uncomfortable with your demonstrated usage. Typically, an exception is not caught in the same function in which it is thrown. Rather, it is propagated until a point where it can be handled appropriately or translated accordingly.

The way you are using it looks like you would be better off just logging the error at the various points and returning from the function immediately. If you want to throw an exception then you should just let it propagate to the caller, i.e., move the try/catch to the caller, or the caller's caller, etc.

It seems to me that you could simplify it to:
function exceptionErrorHandler($errno, $errstr, $errfile, $errline)
{
    $e = new ErrorException($errstr, 0, $errno, $errfile, $errline);
    $e = new mException($e->message, $e->number);
    $e->errorLog();
}
But this seems to miss the point. You probably want to do this instead:
function exceptionErrorHandler($errno, $errstr, $errfile, $errline)
{
    $e = new ErrorException($errstr, 0, $errno, $errfile, $errline);
    throw new mException($e->message, $e->number);
}

set_error_handler('exceptionErrorHandler');

Would you not want/need to catch the exceptions within that last function example?

Do I want to be implementing the try/catch/handeling at "controller" level rather than class then?

Thanks for the advice.

laserlight

knowj wrote:
Would you not want/need to catch the exceptions within that last function example?

Read the PHP manual on ErrorException. I liberally copied the example from there.

Basically, the idea is to translate an error to an exception. You cannot do that if the function does not throw an exception that propagates to the caller.

knowj wrote:
Do I want to be implementing the try/catch/handeling at "controller" level rather than class then?

What do you mean?

knowj

I tried moving the catch block outside outside of the exceptionErrorHandler() function itself and have been left with the following:

"Fatal error: Exception thrown without a stack frame in Unknown on line 0"

function exceptionErrorHandler($errno, $errstr, $errfile, $errline)
	{
		$e = new ErrorException($errstr, 0, $errno, $errfile, $errline);
		throw new mException($e->getMessage(), $e->getCode());
	}
set_error_handler('exceptionErrorHandler');

laserlight

Post the smallest and simplest script that you think should run but which demonstrates the error that you cited.

knowj

Ah I found a rouge snippet of code creating a database object outside of a try block. This seems to have been the problem.

Bit of a poor/unhelpful error... Looks like google has people with the same sorts of issues wondering what it means.