For example trying to print triangle.c with
trueprint triangle.c --language=c --function-index --intelligent-line-wrap  --holepunch -r --file-index --function-index
Doesn't print function index.
You can find triangle from http://www-2.cs.cmu.edu/~quake/triangle.html.
(Yes I know it is not GNU neither copyleft software..... I'll try to solve this)

I have almost solved the problem passing that file throught the C preprocessor, keeping comment and don't printing "# statement", i.e.:
cpp -C -P  triangle.c cpptriangle.c
trueprint cpptriangle.c triangle.h --language=pseudoc --function-index --intelligent-line-wrap  --holepunch -s triangle.ps --file-index --function-index

The problem is that the original triangle.c is a magrovial forest of prepropressor directives (#ifdef, #else et cetera) which confuses trueprint.
Perhaps an option to filter sources with cpp would be useful.