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

Question

I am looking for an example to create a listStore (to use in a treeview) that may contain a progress bar type field.

I am 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 the G_TYPE? I use it to tell listStore that it is a progress bar?