&reftitle.examples;

Below we can see an example of using the error handling capabilities in PHP. We define an error handling function which logs the information into a file (using an XML format), and e-mails the developer if a critical error in the logic happens.

## Using error handling in a script

    <?php
    // we will do our own error handling
    error_reporting(0);

    // user defined error handling function
    function userErrorHandler($errno, $errmsg, $filename, $linenum, $vars)
    {
        // timestamp for the error entry
        $dt = date("Y-m-d H:i:s (T)");

        // define an assoc array of error string
        // in reality the only entries we should
        // consider are E_WARNING, E_NOTICE, E_USER_ERROR,
        // E_USER_WARNING and E_USER_NOTICE
        $errortype = array (
                    E_ERROR              => 'Error',
                    E_WARNING            => 'Warning',
                    E_PARSE              => 'Parsing Error',
                    E_NOTICE             => 'Notice',
                    E_CORE_ERROR         => 'Core Error',
                    E_CORE_WARNING       => 'Core Warning',
                    E_COMPILE_ERROR      => 'Compile Error',
                    E_COMPILE_WARNING    => 'Compile Warning',
                    E_USER_ERROR         => 'User Error',
                    E_USER_WARNING       => 'User Warning',
                    E_USER_NOTICE        => 'User Notice',
                    E_STRICT             => 'Runtime Notice',
                    E_RECOVERABLE_ERROR  => 'Catchable Fatal Error'
                    );
        // set of errors for which a var trace will be saved
        $user_errors = array(E_USER_ERROR, E_USER_WARNING, E_USER_NOTICE);

        $err = "<errorentry>\n";
        $err .= "\t<datetime>" . $dt . "</datetime>\n";
        $err .= "\t<errornum>" . $errno . "</errornum>\n";
        $err .= "\t<errortype>" . $errortype[$errno] . "</errortype>\n";
        $err .= "\t<errormsg>" . $errmsg . "</errormsg>\n";
        $err .= "\t<scriptname>" . $filename . "</scriptname>\n";
        $err .= "\t<scriptlinenum>" . $linenum . "</scriptlinenum>\n";

        if (in_array($errno, $user_errors)) {
            $err .= "\t<vartrace>" . wddx_serialize_value($vars, "Variables") . "</vartrace>\n";
        }
        $err .= "</errorentry>\n\n";

        // for testing
        // echo $err;

        // save to the error log, and e-mail me if there is a critical user error
        error_log($err, 3, "/usr/local/php4/error.log");
        if ($errno == E_USER_ERROR) {
            mail("phpdev@example.com", "Critical User Error", $err);
        }
    }

    function distance($vect1, $vect2)
    {
        if (!is_array($vect1) || !is_array($vect2)) {
            trigger_error("Incorrect parameters, arrays expected", E_USER_ERROR);
            return NULL;
        }

        if (count($vect1) != count($vect2)) {
            trigger_error("Vectors need to be of the same size", E_USER_ERROR);
            return NULL;
        }

        for ($i=0; $i<count($vect1); $i++) {
            $c1 = $vect1[$i]; $c2 = $vect2[$i];
            $d = 0.0;
            if (!is_numeric($c1)) {
                trigger_error("Coordinate $i in vector 1 is not a number, using zero",
                                E_USER_WARNING);
                $c1 = 0.0;
            }
            if (!is_numeric($c2)) {
                trigger_error("Coordinate $i in vector 2 is not a number, using zero",
                                E_USER_WARNING);
                $c2 = 0.0;
            }
            $d += $c2*$c2 - $c1*$c1;
        }
        return sqrt($d);
    }

    $old_error_handler = set_error_handler("userErrorHandler");

    // undefined constant, generates a warning
    $t = I_AM_NOT_DEFINED;

    // define some "vectors"
    $a = array(2, 3, "foo");
    $b = array(5.5, 4.3, -1.6);
    $c = array(1, -3);

    // generate a user error
    $t1 = distance($c, $b) . "\n";

    // generate another user error
    $t2 = distance($b, "i am not an array") . "\n";

    // generate a warning
    $t3 = distance($a, $b) . "\n";

    ?>