If all you want to do is quote a string as you would normally do in PHP (for example, when returning an Ajax result, inside a json string value, or when building a URL with args), don't use addslashes (you don't want both " and ' escaped at the same time). Instead, just use this function:

<?php
function Quote($Str) // Double-quoting only
    {
    $Str=str_replace('"','\"',$Str);
    return '"'.$Str.'"';
    } // Quote
?>

Modify this easily to get a single-quoting function.