PHP-General - SEO url using php

Hello,
Need help with creating seo url using php, I have cattegory list on page cat.php where I generate URL
using this code:

<a href="item.php?id=<?=$values[$i]['itemid']?>&<?=$values[$i]['itemname']?>

As result I get what I want but with bunch of spaces that creates URL with lots of %20
I would like to replace %20 with dash
I can not use mod_rewrite since there is unknown amount of spaces so I need to do it using php.
For one item there are 4 links and I should do it separate for all 4 links so it would be good if there is any way to modify
this line of code or put some code right before it so it points just for that link

Thanks

I believe preg_replace is what you are looking for.

str_replace replaces strings, but explain why you can't use mod rewrite?

Dont know just wont work, I use this rule

RewriteRule ^(/?id=*/[^/]*?)_([^/]*?_[^/]*)$ $1-$2 [N]
RewriteRule ^(/?id=*/[^/]*?)_([^/_]*)$ $1-$2 [R=301]

and thing is that my url does not change, there is still %20, but funny thing is that when I manualy change %20 to - in url and hits Enter, URL is fine with -

With php I have also tried with str_replace or pereg_replace, weather I make it as function or not, I can not make it work just with single link
<a href="item.php?id=<?=$values[$i]['itemid']?>&<?=$values[$i]['itemname']?>

Actually you can't use mod_rewrite because that doesn't fix the URLs you output. str_replace() can replace spaces with hyphens.
Then fix item.php so it does the reverse replacement on the item name.

If you want friendly URLs then that's something completely different.