PHP: Trigger fatal error?

E_USER_ERROR is the suited constant.

trigger_error("Fatal error", E_USER_ERROR);

See also the first example of the manual page and the list of PHP Errors (only ones beginning with E_USER* may be issued from trigger_error).

Note: if you're using a custom error handler (see set_error_handler) E_USER_ERROR will NOT halt/exit/die unless the error handler returns false

nutshell : your custom error handler effectively determines if E_USER_ERROR is treated as a fatal

If you are using PHP 7 or higher, Error class works too:

$flag = false;

try {
    if ($flag == false) {
        throw new Error('An error occured');
    }
} catch (Error $e) {
    echo $e->getMessage();
}

If you put throw new Error('An error occured'); outside the Try Catch, You will get a Fatal Error.

debug_print_backtrace();
trigger_error("As much information as you can provide, please", E_USER_ERROR);
exit();

exit() terminates the PHP script entirely. The more information you can provide users or developers about the error, the better. Error codes are passé.

Edit: use of E_USER_ERROR should terminate the script anyway, so moved debug_print_backtrace() before trigger_error().