Callback system for use in widget libraries, abstract interfaces, and
general programming.

This library implements a full callback system for use in widget
libraries, abstract interfaces, and general programming. Originally part
of the Gtk-- widget set, libsigc++ is now a separate library to provide for
more general use. It is the most complete library of its kind with the
ability to connect an abstract callback to a class method, function, or
function object. It contains adaptor classes for connection of dissimilar
callbacks and has an ease of use unmatched by other C++ callback
libraries.

Package gtkmm, which is a c++ binding to the famous gtk+ library, uses
libsigc++.