This .defs file describes objects and their functions. It is generated by the h2defs.py script which you can find in pygtk's codegen directory. For instance,

$ ./h2defs.py /usr/include/gtk-2.0/gtk/*.h > gtk_methods.defs

This .defs file describes enum types and their possible values. It is generated by the enum.pl script which you can find in glibmm's tools directory. For instance,

$ ./enum.pl /usr/include/gtk-2.0/gtk/*.h > gtk_enums.defs

This .defs file describes signals and properties. It is generated by the special extra_defs utility that is in every wrapping project, such as gtkmm/tools/extra_defs_gen/. For instance

$ cd tools/extra_defs_gen
$ ./generate_extra_defs > gtk_signals.defs

You must edit the source code of your own extra_defs_gen tool in order to generate the .defs for the C types that you wish to wrap. Start by renaming the file:

$ cd tools/extra_defs_gen
$ mv generate_defs_gda.cc generate_defs_example.cc

Then edit the Makefile.am so that it mentions the new file name, and edit the new .cc file to specify the correct types. For instance, your main() function might look like this:

#include <libsomething.h>

int main (int argc, char *argv[])
{
    libexample_init(argc, argv);

    std::cout << get_defs(EXAMPLE_TYPE_SOMETHING)
              << get_defs(EXAMPLE_TYPE_THING);
    return 0;
}