CODEWITHSUNDEEP
cruby
matejuh
matejuh

Reputation: 406

Wrapping C struct to Ruby

How to initialize C Struct and wrap it as Ruby class as parameter of another Ruby object? I am rewriting the memory, but don't know, how to fix it.

Ruby code, I want to create instances of Person class and add Address variable into them, which is another class:

require_relative 'my_extension'

class Address
  def inspect
    "Replaced #inspect: <Address: town:#{town}>"
  end
end

class Person
    def initialize
        puts "init"
    end

    def print()
        puts "Addr class #{@addr.inspect}"
    end
end

foo1=Person.new
foo1.add_address("London")
foo1.print
foo2=Person.new
foo2.add_address("Paris")
foo1.print
foo2.print
foo1.print

C code, extending Ruby:

#include <stdio.h>
#include "ruby.h"

struct Address {
    char * town;
};

static VALUE get_addr(VALUE self) {
    return rb_iv_get(self,"@addr");
}

static VALUE wrap_address_get_town(VALUE self) {

    struct Address * address;
    Data_Get_Struct(self, struct Address, address);
    return rb_str_new2(address->town);
}


VALUE foo_class;
VALUE address_wrapper_class;


void free_m(){
    printf("free\n");//just for test
}

void add_address_t(VALUE self,VALUE new_town){
    printf("add_address\n");
    /*init new struct and add value to it*/
    struct Address addr;
    addr.town=StringValuePtr(new_town);

    /*wrap struct*/
    VALUE wrapped_address=Data_Wrap_Struct(address_wrapper_class, 0, free_m,&addr);

    /*set it as instance variable*/
    rb_iv_set(self,"@addr",wrapped_address);
}

static VALUE foo_class_alloc(VALUE self){
    return self;
}


void Init_my_extension(){
    foo_class = rb_define_class("Person", rb_cObject);

    address_wrapper_class = rb_define_class("Address", rb_cObject);

    rb_define_method(address_wrapper_class, "town", wrap_address_get_town, 0);

    rb_define_method(foo_class, "add_address", add_address_t, 1);

}

Output produces unexpected result:

init
Addr class Replaced #inspect: <Address: town:London>
init
Addr class Replaced #inspect: <Address: town:Paris> //London expected
Addr class Replaced #inspect: <Address: town:�)> //another problem
Addr class Replaced #inspect: <Address: town:�)>
run
run
free
free

Upvotes: 4

Views: 1778

Answers (2)

lottscarson
lottscarson

Reputation: 588

The FFI gem may provide a better way to accomplish what you want to do:

require 'ffi'  
module AddressModule
   extend FFI::Library
   ffi_lib '<path to your c library>'

   class Address < FFI::Struct
      layout :address, :string,
   end
end

person = AddressModule::Address.new
person[:address] = "an address"

Or whatever. Check out the FFI documentation at https://github.com/ffi/ffi/wiki

Upvotes: 1

Aleksander Pohl
Aleksander Pohl

Reputation: 1695

All the C routines should be defined as static returning a VALUE. This should be Qnil, if nothing relevant should be returned. There is also another problem, with the add_address_t routine - you are wrapping a locally defined struct - it should be allocated with ALLOC(struct Address);

Upvotes: 0

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