How do I do drag-and-drop?

GTK+ has a high level set of functions for doing inter-process communication via the drag-and-drop system. GTK+ can perform drag-and-drop on top of the low level Xdnd and Motif drag-and-drop protocols.

The documentation on GTK+ drag-and-drop isn't complete, but there is some information in the Tutorial. You should also look at the drag-and-drop example code that is part of the GTK+ source distribution, in the file gtk/testdnd.c.