callback with multiple parameters

[eluser]Blaskunk[/eluser]
Hello world !

I use a callback like that :

callback_test[todo]

in my function :

test($str='',$string='')
{
echo "00$string00";
}

in fact, my function print "0000", so i don't understand why I don't manage to show "00todo00" ...

Need you to work please !!
Have a nice day !