Exception Handling

captainmerton · 05-17-2009, 08:57 AM

I am using the generic php5 Exception class to "catch" errors in my script. I have the code i want to trap errors from within the "try" clause. However while this is useful for displaying errors I want to perform different code before display of error depending on whether i've caught an error or not. can someone advise what the code would be to do this?

eg.

try {

Do some stuff

If error-caught {
do some error related stuff
}

catch(Exception $error) {
print $error->getMessage();
}

Hightower · 05-17-2009, 09:50 AM

If I'm thinking of the same thing, I believe the way to do this would be to use an error handler:

PHP Code:


			
function custom_error_handler ($e_number, $e_message, $e_file, $e_line, $e_vars) {
}

set_error_handler('customer_error_handler');

You can then set your error message to whatever you want within that function:

PHP Code:


			
$m = "A major mishap took place in '$e_file' on line '$e_line' with the message '$e_message'.";

You can then trigger this custom error in other scripts (so long as you have included this file):

PHP Code:


			
trigger_error('Could not connect with error: ' . mysqli_connect_error());

This is the kind of thing that I'm looking into at the minute, and if I've understood your query properly I think this should help you.

captainmerton · 05-17-2009, 12:20 PM

Here's the code I am messing with (see below) apologies if it isnt easy to read. What i am trying to achieve is i'm happy with catching the error at the end for example but wonder if i can access the error before the end of the script eg. this script will display a login form if you arent logged in already. If you submit an empty form it throws an error which is displayed at the end of the script. However i want to add some code around the form display part to say well if you have submitted the form but an error has bene thrown back then re-display the form code. I guess what i am asking is do i need the catch(Exception $error) code to access the error so i need to nest try statements? Dunno if i am making myself clear but just trying to understand this i.e. before that last statement "catch(Exception $error)" can i access $error or is the catch statement instatitiating an $error object.

Quote:

try {
require_once('./lib/login.class.php');
$login = new Login;

/* Verify the user has login, otherwise redirect to login page */
if($login->verifyAccess()) {
/* User is logged in, display welcome message */
print "Welcome " . $_SESSION['name'];
require_once('inc.loggedin.php');
} else {

/* Check if the form has been submitted. If not, redirect to login page */
if(!isset($_POST['submit'])) {
/* Include the HTML for the form */
require_once('inc.form.php');
}
else {
$username = $_POST['username'];
$password = $_POST['password'];

/* Verify the login details are correct and redirect to secure.php */
$login->verifyLogin($username, $password);
}
}

}
catch(Exception $error) {
print $error->getMessage();
}

Salathe · 05-17-2009, 12:35 PM

My advice would be to not misuse exceptions. They're there to cater for exceptional circumstances: a validation error during the login procedure is something that happens as a matter of course, it is not an exceptional state in my opinion.

If you do want to continue using exceptions in this nature, perhaps focus on capturing specific types of exceptions and have a more narrow focus on the code between the try and catch. Consider catching only LoginValidationException or some such before you fall back to a generic exception.

captainmerton · 05-17-2009, 01:07 PM

Thanks for the advice. I believe I can extend the class to cover specific types of exception.