How do I define a listStore to render a progress bar in gtk2?

I'm looking for an example to create a listStore (to use in a treeView) that can contain a field of type progress bar.

I'm writing in C (not in c ++) and using gtk2 in my code:

store=gtk_liststore_new(3,G_TYPE_STRING,G_TYPE_INT, G_TYPE???);

So what is G_TYPE ? I use it to tell the listStore what a progress bar is?