3D object filling

I have drawn a 3D object(cube) using GL_QUADS.I want to fill the object’s interior space so that after clipping it remains solid
(all the surfaces are filled…i.e.no hole).how can I do it?

Sounds a bit like homework assignment to learn about the stencil buffer…

See http://www.opengl.org/resources/code/samples/advanced/advanced97/notes/node10.html for a technique.