Using PHP Error Handling Page 2

Throwing errors from PHP pages

Throwing errors from a PHP page is quite the same as emulating Apache’s behaviour for ErrorDocument
directives, you simply redirect the user using a query-string that specifies variables that
Apache usually sets as environment variables. This makes it possible to use the same error page
for all kinds of errors. An example:

<?php
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 be able to throw errors anywhere on this page.
if(!condition) {
    throw_error("the condition failed");
}
ob_end_flush(); // Page rendered, flush the output buffer.
?>

Using the PHP4 feature called output buffering also helps creating generic error reporting
functionality. By not flushing the output buffer until you are sure the whole page has rendered
error-free, you are able to make Header calls anywhere in your code to redirect the user.

I’ll leave up to the reader to design and implement his/her own error.php page to suit his/her site.
Don’t forget that you can include a form with email submission possibilities for the users to send
you comments.