Nontrivial examples of C interface with Ada

[gressett@iglobal.net]

Is there an example of a well-done, nontrivial interface to a C
library readily available on the web? Examples of communication with
C things defined like

some_struct *c_function(const char *things[]);

char *things[] = {
  "a",
  "b",
  "c",
  NULL
};

or

void c_routine(some_struct *p, void *otherthings[]);

or

int c_function2(int numbers[]);


would be very nice to have.
(Was it Mark Twain who said, "Learning by example isn't the best way,
it's the only way."?)