PHP error interface_PHP tutorial

One of the most common mistakes on the web is invalid links. As soon as invalid links appear from other sites, you will rearrange your
site. People will bookmark a site they like, and if they come back three months later and all they see is a '404 Not Fount '
, they won't be given the task of telling them how to get there from your site. Go find the original information. Let's fix this, or at least
give your users some friendly help and some trace once they encounter a 'a 404' error. You can create a normal page to
report all errors encountered while processing your page.

PHP together with Apache gives you the freedom to create your own error pages, but it requires reconfiguration and a small amount of
coding. Let's learn the configuration part first.

Apache's ErrorDocument directive is used to indicate which document (or URI) Apache should redirect to when an error occurs. It allows you to
specify a resource for each error code your users may encounter. By adding an ErrorDocument 404
/error.php directive to your server configuration. This will redirect the user to 'error.php' when they access a page that does not exist. Below we will write the
'error.php' page. Don't forget to restart Apache for the changes to take effect.

Next, we write a simple error.php:

The file you requested ( ) does not exist on this server.
Please find the file you want from previous page.

Now try to read a page that does not exist on your server. How about, you can see error.php, it has a nice and
friendly message, and there is also a to Link to previous page.

Let’s expand this a bit. As you can see, I'm using the REDIRECT_URL variable in error.php. This variable is set by Apache when
executes an ErrorDocument directive, and gives a possibility to find the original resource. In this case, Apache
also sets some other variables, all of which can be found here. Using these variables it is possible to create a nice error page that gives
users a nice and friendly error page instead of the default page given by Apache.

Outputting errors from a PHP page
Outputting errors from a PHP page is much like simulating what Apache does with the ErrorDocument directive, you simply redirect the user,
by using query-string Variables, while Apache is usually set in environment variables. This way you can use the same error page to
handle various errors. Here is an example:




function throw_error($message) {
$error_page = "/err/error.php";

$error_url = $error_page;
$error_url .= "?REDIRECT_ERROR_NOTES=$message";
$error_url .= "&REDIRECT_URL=" . $GLOBALS["PHP_SELF"];
$ error_url .= "&REDIRECT_REQUEST_METHOD=$REQUEST_METHOD";
$error_url .= "&REDIRECT_STATUS=501";
Header("Status: 501");
Header("Location: $error_url");
exit;
}

ob_start();
// Use output buffering to output errors anywhere in this page

if(!condition) {
throw_error("the condition failed");
}

ob_end_flush();
// After the page is processed, refresh the output buffer
?>
Use the output buffering feature of PHP4 It will also be helpful to generate general error reporting capabilities. But when you confirm that the entire error page has been processed
, don’t forget to refresh the buffer. You can redirect through the Header call anywhere in your code.​