If you use one signal handler to catch the same signal from several widgets,
you might like that signal handler to receive some extra information. For
instance, you might want to know which button was clicked. You can do this with
sigc::bind(). Here's some code from the helloworld2 example.
m_button1.signal_clicked().connect(sigc::bind(sigc::mem_fun(*this, &HelloWorld::on_button_clicked), "button 1"));
This says that we want the signal to send an extra
Glib::ustring argument to the signal handler, and that
the value of that argument should be "button 1". Of course we will need to add
that extra argument to the declaration of our signal handler:
void on_button_clicked(const Glib::ustring& data);
Of course, a normal "clicked" signal handler would have no arguments.
sigc::bind() is not commonly used, but you might find it
helpful sometimes. If you are familiar with GTK
programming then you have probably noticed that this is similar to the extra
gpointer data arguments which all GTK callbacks have. This
is generally overused in GTK to pass information
that should be stored as member data in a derived widget, but widget derivation
is very difficult in C. We have far less need of this hack in gtkmm.