如何确保我的PHP在所有服务器环境中都可移植？

Question

It's not a rare thing for me to deploy PHP to a server, or move it from one server to another, and have it completely fail with database or cookie errors. I'd like to get better at avoiding these kinds of issues before they happen.

What are some potential portability problems in PHP, with regards to different servers, OS's, and PHP configurations, and how can they be worked around? Let's assume that I (unfortunately) have no control over the server environment, besides FTP. (I'll add one answer to get things started)

Answer 1

Some servers are configured with magic quotes enabled (magic_quotes_gpc=1 in php.ini), which automatically calls addslashes() on $_GET, $_POST, $_COOKIE, and $_REQUEST. It was originally introduced to help beginners unknowningly write more secure code, but its use is now depreciated.

To simulate disabling this misfeature at runtime if it's enabled, run the following code before using any of the request vars (adapted from this comment):

function destroyTheMagic($array, $topLevel = true) {
    $ret = array();
    foreach($array as $key => $value) {
        if(!$topLevel)
            $key = stripslashes($key);
        if(is_array($value))
            $ret[$key] = destroyTheMagic($value, false);
        else
            $ret[$key] = stripslashes($value);
    }
    return $ret;
}

if(get_magic_quotes_qpc()) {
    $_GET = destroyTheMagic($_GET);
    $_POST = destroyTheMagic($_POST);
    $_COOKIE = destroyTheMagic($_COOKIE);
    $_REQUEST = destroyTheMagic($_REQUEST);
}