PHP将String vars作为数组访问并更改值

Question

Is it ok to do this please?

for($i=0;$i<strlen($str);$i++)
{
    if(!in_array($str[$i],$arAllowedCharset)){$str[$i]='';}
}
return $str;

It works, but I am unsure if I am "allowed" to do that, ie $str[$i]=''; .
Note: $str is a string variable, $arAllowedCharset is an array containing only alphanumerical characters and a dash.

I use that to format user-submitted URLs in a custom CMS.

Thank you.

Answer 1

It would be easier to check and correct the url with a regular expression. For example

$str = preg_replace('#[^a-z0-9-]#i', '', $str);