How can I get the device number of a partition before it's created?

[Hauke Goos-Habermann]

Hi,

I'm working on a web based frontend (PHP) for parted for our software 
distribution system m23 (m23.sf.net), that allows me to remove, add and 
format partitions. The interface showes me how the new partitionating will 
look like before it is actualy done. So I've to know how the partitions are 
numbered (e.g. hda1, hda2, ...). After each operation the web page is updated 
and shows me the new look of the partitioning.

What I don't understand is the numbering of the newly created partitions. 
Sometimes they get reordered and sometimes not. If I delete a partition and 
create two new in that space the numbering is not always recalculaded. Till 
now I haven't found the algorithm how it is done.

Can somebody help me?

Regards Hauke