Example of embedding Ruby interpreter into C/C++ program

main.cpp

// very basic embedded Ruby interpreter for C++ programs
// thrown together by Jeff Trull <jetrull@sbcglobal.net> based on googling and asking questions on #ruby-lang
#include <ruby.h>

// access to C variables
static VALUE getter(VALUE ns, VALUE var) {
  return Qfalse;
}

VALUE setter(VALUE ns, VALUE var, VALUE val) {
  return Qfalse;
}

RUBY_GLOBAL_SETUP

int main(int argc, char **argv) {
  ruby_sysinit(&argc, &argv);
  RUBY_INIT_STACK;
  ruby_init();

  // provide interactive prompt with irb (the Ruby shell) by telling ruby to execute it on startup
  // copy arg array and add this option at the end
  char** new_argv = (char**)malloc((argc + 2) * sizeof(char*));
  for (int i = 0; i < argc; i++) {
    new_argv[i] = argv[i];
  }
  new_argv[argc] = "-e";
  new_argv[argc+1] = "require \"irb\"; IRB.start";

   // create some modules
  VALUE mymod = rb_define_module("MOD");
  rb_define_module_function(mymod, "setparam", setter, 3);
  rb_define_module_function(mymod, "getparam", getter, 2);

  return ruby_run_node(ruby_options(argc+2, new_argv));
}

I am getting the same compile error with the variadic arguments.

You have to reininterpret-cast the argument you use:
rb_define_module_function(mymod, "setparam", reininterpret_cast< VALUE ( * ) ( ... ) >(setter), 3);
I do not say anything wrong, but so far as i know it's a C to C++ problem.