exception vs die

freenity · 02-27-2008, 10:27 PM

Hi
Well I have never used exceptions, but see some people do, so what is the main difference between those exceptions and die() or echo() and exit() ??

abiko · 02-27-2008, 10:43 PM

From my viewpoint:
exceptions are the way to go.
Why? Because it's the right way to debug your application if something goes wrong.

Let's use die() for example - it just stops your script. You have to put some code which you want to print out as your debug info.

Exceptions - insystem function that prints the error if any occured on specific part of your code.

Example:

PHP Code:


			
<?php

    

    function test( $t ) {

        

        if ( !is_numeric( $t) ) {

            throw new Exception ("You must use only numeric values");

        } else {

            echo $t;

        }

    }

    

    test( '1');

    test( '2');

    test( 'aa' );

?>

Output:

Code:

12
Fatal error: Uncaught exception 'Exception' with message 'You must use only numeric values' in E:\xampplite\htdocs\test\ex.php:6 Stack trace: #0 E:\xampplite\htdocs\test\ex.php(14): test('aa') #1 {main} thrown in E:\xampplite\htdocs\test\ex.php on line 6

The second example:

PHP Code:


			
<?php

    

    function test( $t ) {

        

        if ( !is_numeric( $t) ) {

            throw new Exception ("You must use only numeric values");

        } else {

            echo $t;

        }

    }

    

    

    try {

    test( 'a');

}



catch( Exception  $e ) {

        echo $e->getMessage();

}

?>

outputs:
You must use ony numerical values.

So the bottom line:
Error handling is improved.
You can assign your custom error message if there is an error, and you user try{} catch{}.

For me it's the way to go.

Can't wait what the others have to say

Please correct me if I was wrong about something.

freenity · 02-27-2008, 10:53 PM

So the execution will go directly to

PHP Code:


			
catch( Exception  $e ) {

        echo $e->getMessage();

if the exception occurs?

abiko · 02-27-2008, 10:56 PM

Yes.
Let's say you have a multilingual site.

PHP Code:


			
<?php

    

    function test( $t ) {

        global $lang;

        if ( !is_numeric( $t) ) {

            throw new Exception ($lang->NUMERIC_ERROR);

        } else {

            echo $t;

        }

    }

    

    

    try {

    test( 'a');

}



catch( Exception  $e ) {

       // Some error managment

$tmpl->addVar( 'error', $e->getMessage() );

$tmpl->activate( 'errorLayout' );



}

?>

For example.

freenity · 02-27-2008, 10:59 PM

ok I see :)
Starting to understand it

xenon · 02-27-2008, 11:14 PM

The exceptions are not a way of ending your script. die and exit are made for that. Exceptions are used to treat various cases and act accordingly. For example:

Code:

function do_division($a, $b)
{
    if( $b == 0 )
   {
        throw new Exception('The divisor cannot be 0!');
   }

    return ($a / $b);
}

try
{
    echo 'Result: ' . do_division(2, 0);
}
catch(Exception $e)
{
    echo $e->getMessage();
    
   // use some default values
   $a = 4;
   $b = 2;
}

// continue execution ...

wGEric · 02-27-2008, 11:16 PM

What about makes using exceptions better than using trigger_error or overwriting that with your own error handler using set_error_handler or calling your own error function?

To me exceptions aren't worth it since you have to use try/catch blocks when I could just use a trigger_error or something similar right where I want the error to be spit out.

I guess if a function or something could return different types of errors then setting up multiple catch blocks would be good. But then again there's ways to do that without using exceptions.

Alan @ CIT · 02-27-2008, 11:55 PM

For all questions regarding the advantages and disadvantages of using Exceptions, I refer you to PHP5 Exception Use Guidelines :) Although it is targetted at PEAR developers it is well worth a read, particularly for folks who are new to Exceptions.

Alan