resource C_externals()
   external getpid() returns int # UNIX system call returning process id
                                 # supported by C runtime library
   external which_bits_set(ref bits_are_set[*] : int; set_of_bits : int)
                                 returns int # user-defined C function
   var pid : int
   var num_bits_set : int
   var bits_are_set[32] : int
   pid := getpid()
   num_bits_set := which_bits_set(bits_are_set, pid)
   write("the pid is", pid, "and it has", num_bits_set, "bits set:")
   fa i := 1 to num_bits_set -> writes(" ", bits_are_set[i]) af; write()
end C_externals

/* ............... Example compile and run(s)

% sr -v; sr -c C_externals.sr
SR version 2.3, October 1994
% cc -c which_bits_set.c
% srl -o C_ext_test which_bits_set.o C_externals
% ./C_ext_test
the pid is 28230 and it has 8 bits set:
 1 2 6 9 10 11 13 14
% ./C_ext_test
the pid is 28231 and it has 9 bits set:
 0 1 2 6 9 10 11 13 14
% ./C_ext_test
the pid is 28232 and it has 7 bits set:
 3 6 9 10 11 13 14
                                              */