Some of the example programs use hardcoded file names generated by other programs.
Here follows a way to run the programs :

interpol_curve_free    curve1.dat  interpol_curve1_free.g2
interpol_curve_hermite curve2.dat  interpol_curve2_hermite.curve.g2  interpol_curve2_hermite.points.g2
closestpoint_curve
closestpoint_degenerate_sf
closestpoint_surface
const_param_curves
append_curve   spline_ellipse_segm_org.g2  interpol_curve1_free.g2  0  append0.g2
approx_curve   0.2
approx_surface 0.01
circle
project_curve 0.001
ellipse
sphere
cylinder
cone
torus
surface_of_revolution
adapt_curve 0.05
coons_patch_gen
linear_swept_surface
rotational_swept_surface
