php通过引用传递

Question

What's wrong with this program? It never returns done and the mail never goes out. if you remove getOrDefault function it works fine. It doesn't throw an error or an exception on php 5.3.13

<?php

    function getOrDefault(&$var, $default = null) {
        // because I'm tired of typing $x = isset($_POST['x'])? $_POST['x']:null;
        if (isset($var)) {
            return $var;
        } else {
            return $default;
        }
    }

    $HTTP_CLIENT_IP = getOrDefault($_SERVER['HTTP_CLIENT_IP']);

    mail('[e-mail]', 'test', $HTTP_CLIENT_IP);
    echo 'done';
?>

Answer 1

You don't need this

$HTTP_CLIENT_IP = getOrDefault($_SERVER['HTTP_CLIENT_IP']);

because you can use this

$HTTP_CLIENT_IP = isset($_SERVER['HTTP_CLIENT_IP'])?$_SERVER['HTTP_CLIENT_IP']:$default;