CODEWITHSUNDEEP
crubyirb
rhavin
rhavin

Reputation: 1689

Extending Ruby with c – module returns strange value, please explain…

I'm currently testing c-extending ruby. The following test-module compiles and gets installed:

# include "ruby.h"

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

static VALUE t_check(VALUE self)
{
  return 15;
}

VALUE Qmodule;
VALUE FlagValueClass;

void Init_Flags()
{
  Qmodule = rb_define_module("Q");
  FlagValueClass = rb_define_class_under(Qmodule, "Flags", rb_cObject);
  rb_define_method(FlagValueClass, "initialize", t_init, 0);
  rb_define_method(FlagValueClass, "check", t_check, 0);
}

But when I load it into irb:

1.9.3-p286 :002 > require 'Q/Flags'
 => true
1.9.3-p286 :003 > a = Q::Flags
 => Q::Flags
1.9.3-p286 :004 > a = Q::Flags.new
 => #<Q::Flags:0x00000001fa78e0>
1.9.3-p286 :005 > puts a.check()
 => 7

…I get 7 instead of 15 which I would expect. Could someone please explain what is happening here?

Upvotes: 0

Views: 68

Answers (1)

rhavin
rhavin

Reputation: 1689

OK; after trying to return a string and getting a dump, i finally got it … ^^

My fault was to not read the documentation (especially the macros in ruby.h) carefully: by returning 15, Ruby gets 0xF wich has the LSB set. Therefore it sees a fixnum, wich gets its value by shifting it one bit right, so it ends as 0x7. By returning INT2FIX(15) instead of just 15, this gets solved.

Upvotes: 2

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