c++-gtk-utils is a lightweight library containing a number of
classes and functions for programming GTK+ programs using C++ in
POSIX (unix-like) environments, where the user does not want to
use a full-on wrapper such as gtkmm or wxWidgets, or is concerned
about exception safety or thread safety of the wrapper and their
documentation. It is parallel installable for both GTK+2 and GTK+3.
There is also an option to install a subset of the library with
only glib/gobject/gio support, without GTK+.

Homepage:
https://cxx-gtk-utils.sourceforge.net/
