php - How to catch an unexpected error?

Question

I'm writing a script, where a lot of things could go wrong. I'm making if/else statements for the obvious things, that could heppen, but is there a way to catch something, that could possible heppen, but I don't know what it is yet?

For example something causes an error of some kind, in the middle of the script. I want to inform the user, that something has gone wrong, but without dozens of php warning scripts.

I would need something like

-- start listening && stop error reporting --

the script

-- end listening --

if(something went wrong)
$alert = 'Oops, something went wrong.';
else
$confirm = 'Everything is fine.'

Thanks.

Answer 1

Why not try...catch?

$has_errors = false;    
try {
  // code here

} catch (exception $e) {    
  // handle exception, or save it for later
  $has_errors = true;
}

if ($has_errors!==false)
  print 'This did not work';

Edit:

Here is a sample for set_error_handler, which will take care of any error that happens outside the context of a try...catch block. This will also handle notices, if PHP is configured to show notices.

based on code from: http://php.net/manual/en/function.set-error-handler.php

set_error_handler('genericErrorHandler');

function genericErrorHandler($errno, $errstr, $errfile, $errline) {
    if (!(error_reporting() & $errno)) {
        // This error code is not included in error_reporting
        return;
    }

    switch ($errno) {
    case E_USER_ERROR:
        echo "<b>My ERROR</b> [$errno] $errstr<br />\n";
        echo "  Fatal error on line $errline in file $errfile";
        echo ", PHP " . PHP_VERSION . " (" . PHP_OS . ")<br />\n";
        echo "Aborting...<br />\n";
        exit(1);
        break;

    case E_USER_WARNING:
        echo "<b>My WARNING</b> [$errno] $errstr<br />\n";
        break;

    case E_USER_NOTICE:
        echo "<b>My NOTICE</b> [$errno] $errstr<br />\n";
        break;

    default:
        echo "Unknown error type: [$errno] $errstr<br />\n";
        break;
    }

    /* Don't execute PHP internal error handler */
    return true;
}
$v = 10 / 0 ;
die('here'); 

Answer 2

Read up on Exceptions:

try {
   // a bunch of stuff
   // more stuff
   // some more stuff
} catch (Exception $e) {
   // something went wrong
}

Answer 3

 throw new Exception('Division by zero.');    
try {
    echo inverse(5) . "\n";
    echo inverse(0) . "\n";
} catch (Exception $e) {
    echo 'Caught exception: ',  $e->getMessage(), "\n";
}

http://php.net/manual/en/language.exceptions.php

Answer 4

You should definitely use the try-catch syntax to catch any exception thrown by your script.
Additionally you can extend exceptions and implement new ones that fulfill your needs.This way, you can throw your own exceptions when you find any other kind of unexpected error (error for your script's logic).
A very short example explaining the use of extending exceptions :

 //your own exception class
 class limitExceededException extends Exception { ... }

 try{
 // your script here
 if($limit > 10)
     throw new limitExceededException();
 }catch(limitExceededException $e){//catching only your limit exceeded exception
     echo "limit exceeded! cause : ".$e->getMessage(); 
 }catch(Exception $e){//catching all other exceptions
     echo "unidentified exception : ".$e->getMessage(); 
 }

Answer 5

Besides using try/catch, I think it's important to consider if you should catch an unexpected error. If it's unexpected then your code has no idea how to handle it and allowing the application to continue may produce bad data or other incorrect results. It may be better to just let it crash to an error page. I just recently had a problem where someone had added generic exception handlers to everything, and it hid the original location of the exception making the bug difficult to find.