PHP/MySQL: What should I use to manage errors?

PHP has in-built function to catch various types of errors:

set_error_handler

You should use this function to capture the errors across all your pages, you can write custom code whether to insert errors to database, or to write into separate error log file, or to notify immediately through email to developers, you can decide.

I would start by using

 try 
    { 
     //your code here 
     } 
 catch(Exception $ex) 
     { 
     echo $ex->getMessage();
     }

When doing database queries. The error handling can be loggin it to a file or something like that. That way you catch what's happening and set yourself what needs to be done....

error_reporting(E_ALL);
ini_set('display_errors','On');

ini_set('error_log', 'error.log');
ini_set('log_errors', 'On');

These functions will show errors if any also it will list errors in error.log. If you want to hide the errors from appearing on site then you can set value from "on" to "off". If you want to hide it only from users and not for developers then you can set "ini_set('display_errors','off');" so these will not visible to users but developers can resolve it from error.log

How should I manage these errors?

You should record them and analyse the logs to resolve them (or at least ensure your site is secure).

Should I save them all in a database?

No - you're going to lose visibility of database connectivity issues. The right way is via the syslog functionality on the local machine.

How do I know which errors could occurr?

? All of them.

Handling errors is one of the most important aspects of an application. The users expects it to work, but when an error occurs their may loose confidence into your application, no matter who good it is. I learned it the hard way.

We use a class similar to the following:

class ErrorHandler
{   
    public static function registerHandlers()
    {
        $inst = new ErrorHandler;
        set_error_handler(array(&$inst, 'errorHandler'), E_ALL);
        set_exception_handler(array(&$inst, 'exceptionHandler'));
        register_shutdown_function(array(&$inst, 'shutdownHandler'));
    }

    public function shutdownHandler()
    {
        if (($error = error_get_last()))
        {
            $this->_clearOutputBuffers();
            // Handle error
        }
    }

    public function errorHandler($errno, $errstr, $errfile, $errline, $errcontext)
    {
        $this->_clearOutputBuffers();
        // Handle error
    }

    public function exceptionHandler(Exception $exception)
    {   
        $this->_clearOutputBuffers();
        // Handle error
    }

    private function _getErrorCode($sMessage, $sFile, $nLine, $nCode)
    {
        $errorCode = sprintf("%u", crc32($sMessage.$sFile.$nLine.$nCode));
    }

    private function _clearOutputBuffers()
    {
        if (count(ob_list_handlers()) > 0)
        {
            ob_clean();
        }
    }
}

This class is able to catch most errors and works surprisingly well for debugging purposes as well. When ever an error is caught we write all the information to a file that we can reference later. Further we separate our environments between development and production and have separate error screens for it.

For the development environment we use an error screen that displays the extract of the file a stack trace and variables.

For the production environment we display an error screen containing the error number returned from _getErrorCode. If a customer wants to contact us about the error, all he has to do is tell us the number and we can instantly look it up and have all the data in front of us.

I have attached a screenshot of our development error screen.