using mrb_class_define_method.

mruby_int_bug.c

/*
gcc -I mruby/include -I mruby/src -O3 -g -Wall -Werror-implicit-function-declaration mruby_int_bug.c -lm mruby/mrblib/mrblib.o -lm mruby/lib/libmruby.a
*/

#include <string.h>
#include "mruby.h"
#include "mruby/proc.h"
#include "mruby/compile.h"

mrb_value mrb_num_get(mrb_state *mrb, mrb_value str)
{
    return mrb_fixnum_value(100);
}

mrb_value mrb_st_get(mrb_state *mrb, mrb_value str)
{
    return mrb_str_new(mrb, "hoge", strlen("hoge"));
}

int main() {
    int n;
    mrb_state* mrb;
    struct mrb_parser_state* p;
    struct RClass *class;
    //struct RClass *class_int;

    mrb = mrb_open();

    //class = mrb_define_class(mrb, "Checkbug", mrb->object_class);
    class = mrb_define_module(mrb, "Checkbug");
    //class_int = mrb_define_class_under(mrb, class, "Check", mrb->object_class);
    //mrb_define_method(mrb, class_int, "int", mrb_num_get, ARGS_NONE());
    //mrb_define_method(mrb, class_int, "st", mrb_st_get, ARGS_NONE());
    mrb_define_class_method(mrb, class, "int", mrb_num_get, ARGS_NONE());
    mrb_define_class_method(mrb, class, "st", mrb_st_get, ARGS_NONE());

    char* code =
"require 'Checkbug'                \n"
"puts('-------------------')       \n"
"puts(Checkbug.st)       \n"
"puts(Checkbug.int)      \n"
"puts(Checkbug.st)       \n"
"puts('-------------------')       \n";

    p = mrb_parse_string(mrb, code);
    n = mrb_generate_code(mrb, p->tree);
    mrb_pool_close(p->pool);
    mrb_run(mrb, mrb_proc_new(mrb, mrb->irep[n]), mrb_nil_value());

    return 0;
}