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Maybe I'm missing it somewhere in the PHP manual, but what exactly is the difference between an error and an exception? The only difference that I can see is that errors and exceptions are handled differently. But what causes an exception and what causes an error?
903
The error indicates trouble that primarily occurs due to the scarcity of system resources. The exceptions are the issues that can appear at runtime and compile time. 2. It is not possible to recover from an error.
With PHP 5 came a new object oriented way of dealing with errors. Exception handling is used to change the normal flow of the code execution if a specified error (exceptional) condition occurs. This condition is called an exception.
An exception is an object that describes an error or unexpected behaviour of a PHP script. Exceptions are thrown by many PHP functions and classes. User defined functions and classes can also throw exceptions. Exceptions are a good way to stop a function when it comes across data that it cannot use.
Facilitates Error Handling To say the least, handling fatal and catchable fatal errors has never been an easy task for PHP coders. The new Engine Exceptions will allow you to replace these kinds of errors with exceptions. If the exception is missed, PHP will continue to return the same fatal errors in the current 5.
Exceptions are thrown - they are intended to be caught. Errors are generally unrecoverable. Lets say for instance - you have a block of code that will insert a row into a database. It is possible that this call fails (duplicate ID) - you will want to have a "Error" which in this case is an "Exception". When you are inserting these rows, you can do something like this
try {
$row->insert();
$inserted = true;
} catch (Exception $e) {
echo "There was an error inserting the row - ".$e->getMessage();
$inserted = false;
}
echo "Some more stuff";
Program execution will continue - because you 'caught' the exception. An exception will be treated as an error unless it is caught. It will allow you to continue program execution after it fails as well.
100
I usually set_error_handler to a function that takes the error and throws an exception so that whatever happens i'll just have exceptions to deal with. No more @file_get_contents just nice and neat try/catch.
In debug situations i also have an exception handler that outputs an asp.net like page. I'm posting this on the road but if requested I will post example source later.
edit:
Addition as promised, I've cut and pasted some of my code together to make a sample.
<?php
define( 'DEBUG', true );
class ErrorOrWarningException extends Exception
{
protected $_Context = null;
public function getContext()
{
return $this->_Context;
}
public function setContext( $value )
{
$this->_Context = $value;
}
public function __construct( $code, $message, $file, $line, $context )
{
parent::__construct( $message, $code );
$this->file = $file;
$this->line = $line;
$this->setContext( $context );
}
}
/**
* Inspire to write perfect code. everything is an exception, even minor warnings.
**/
function error_to_exception( $code, $message, $file, $line, $context )
{
throw new ErrorOrWarningException( $code, $message, $file, $line, $context );
}
set_error_handler( 'error_to_exception' );
function global_exception_handler( $ex )
{
ob_start();
dump_exception( $ex );
$dump = ob_get_clean();
// send email of dump to administrator?...
// if we are in debug mode we are allowed to dump exceptions to the browser.
if ( defined( 'DEBUG' ) && DEBUG == true )
{
echo $dump;
}
else // if we are in production we give our visitor a nice message without all the details.
{
echo file_get_contents( 'static/errors/fatalexception.html' );
}
exit;
}
function dump_exception( Exception $ex )
{
$file = $ex->getFile();
$line = $ex->getLine();
if ( file_exists( $file ) )
{
$lines = file( $file );
}
?><html>
<head>
<title><?= $ex->getMessage(); ?></title>
<style type="text/css">
body {
width : 800px;
margin : auto;
}
ul.code {
border : inset 1px;
}
ul.code li {
white-space: pre ;
list-style-type : none;
font-family : monospace;
}
ul.code li.line {
color : red;
}
table.trace {
width : 100%;
border-collapse : collapse;
border : solid 1px black;
}
table.thead tr {
background : rgb(240,240,240);
}
table.trace tr.odd {
background : white;
}
table.trace tr.even {
background : rgb(250,250,250);
}
table.trace td {
padding : 2px 4px 2px 4px;
}
</style>
</head>
<body>
<h1>Uncaught <?= get_class( $ex ); ?></h1>
<h2><?= $ex->getMessage(); ?></h2>
<p>
An uncaught <?= get_class( $ex ); ?> was thrown on line <?= $line; ?> of file <?= basename( $file ); ?> that prevented further execution of this request.
</p>
<h2>Where it happened:</h2>
<? if ( isset($lines) ) : ?>
<code><?= $file; ?></code>
<ul class="code">
<? for( $i = $line - 3; $i < $line + 3; $i ++ ) : ?>
<? if ( $i > 0 && $i < count( $lines ) ) : ?>
<? if ( $i == $line-1 ) : ?>
<li class="line"><?= str_replace( "\n", "", $lines[$i] ); ?></li>
<? else : ?>
<li><?= str_replace( "\n", "", $lines[$i] ); ?></li>
<? endif; ?>
<? endif; ?>
<? endfor; ?>
</ul>
<? endif; ?>
<? if ( is_array( $ex->getTrace() ) ) : ?>
<h2>Stack trace:</h2>
<table class="trace">
<thead>
<tr>
<td>File</td>
<td>Line</td>
<td>Class</td>
<td>Function</td>
<td>Arguments</td>
</tr>
</thead>
<tbody>
<? foreach ( $ex->getTrace() as $i => $trace ) : ?>
<tr class="<?= $i % 2 == 0 ? 'even' : 'odd'; ?>">
<td><?= isset($trace[ 'file' ]) ? basename($trace[ 'file' ]) : ''; ?></td>
<td><?= isset($trace[ 'line' ]) ? $trace[ 'line' ] : ''; ?></td>
<td><?= isset($trace[ 'class' ]) ? $trace[ 'class' ] : ''; ?></td>
<td><?= isset($trace[ 'function' ]) ? $trace[ 'function' ] : ''; ?></td>
<td>
<? if( isset($trace[ 'args' ]) ) : ?>
<? foreach ( $trace[ 'args' ] as $i => $arg ) : ?>
<span title="<?= var_export( $arg, true ); ?>"><?= gettype( $arg ); ?></span>
<?= $i < count( $trace['args'] ) -1 ? ',' : ''; ?>
<? endforeach; ?>
<? else : ?>
NULL
<? endif; ?>
</td>
</tr>
<? endforeach;?>
</tbody>
</table>
<? else : ?>
<pre><?= $ex->getTraceAsString(); ?></pre>
<? endif; ?>
</body>
</html><? // back in php
}
set_exception_handler( 'global_exception_handler' );
class X
{
function __construct()
{
trigger_error( 'Whoops!', E_USER_NOTICE );
}
}
$x = new X();
throw new Exception( 'Execution will never get here' );
?>
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