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

main.cpp

// very basic embedded Ruby interpreter for C++ programs
// thrown together by Jeff Trull <[email protected]> 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));
}

@jlebrech: You can do it by using the following (assuming that you have Ruby's headers installed on your system with Ruby 1.9.3-p286):

$ g++ main.cpp `pkg-config --cflags --libs ruby-1.9` -o testapp

However, I'm getting an error:

 $ g++ -c main.cpp `pkg-config --cflags --libs ruby-1.9`
main.cpp: In function ‘int main(int, char**)’:
main.cpp:27:20: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]
main.cpp:28:22: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]
main.cpp:32:58: error: invalid conversion from ‘VALUE (*)(VALUE, VALUE, VALUE) {aka long unsigned int (*)(long unsigned int, long unsigned int, long unsigned int)}’ to ‘VALUE (*)(...) {aka long unsigned int (*)(...)}’ [-fpermissive]
In file included from /home/jacky/.local/include/ruby-1.9.1/ruby.h:32:0,
                 from main.cpp:3:
/home/jacky/.local/include/ruby-1.9.1/ruby/ruby.h:1101:6: error:   initializing argument 3 of ‘void rb_define_module_function(VALUE, const char*, VALUE (*)(...), int)’ [-fpermissive]
main.cpp:33:58: error: invalid conversion from ‘VALUE (*)(VALUE, VALUE) {aka long unsigned int (*)(long unsigned int, long unsigned int)}’ to ‘VALUE (*)(...) {aka long unsigned int (*)(...)}’ [-fpermissive]
In file included from /home/jacky/.local/include/ruby-1.9.1/ruby.h:32:0,
                 from main.cpp:3:
/home/jacky/.local/include/ruby-1.9.1/ruby/ruby.h:1101:6: error:   initializing argument 3 of ‘void rb_define_module_function(VALUE, const char*, VALUE (*)(...), int)’ [-fpermissive]

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.