# Extendig ruby: defining classes and creating objects from c **URL:** \ **Category:** Ruby\ **Created:** [October 19, 2007, 5:56pm UTC](https://www.ruby-forum.com/t/extendig-ruby-defining-classes-and-creating-objects-from-c/117716 "2007-10-19T17:56:16Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![libit](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/8baadc/32.png) [@libit](https://www.ruby-forum.com/u/libit)\ **Post date:** [October 19, 2007, 5:56pm UTC](https://www.ruby-forum.com/t/extendig-ruby-defining-classes-and-creating-objects-from-c/117716/1 "2007-10-19T17:56:16Z")
I can’t manage to define a new class (actually an exception) and then instantiating it from C. I define the class with: xr\_cException = rb\_define\_class\_under(xr\_module, “Exception”, rb\_eRuntimeError); rb\_define\_method(xr\_cException, “initialize”, xr\_cException\_initialize, 4); … static VALUE xr\_cException\_initialize(VALUE self, VALUE status, VALUE lasterror, VALUE function, VALUE msg) { rb\_iv\_set(self, “@status”, status); rb\_iv\_set(self, “@lasterror”, lasterror); rb\_iv\_set(self, “@function”, function); rb\_iv\_set(self, “@msg”, msg); return self; At this point I can write a ruby test program like a=MYMOD::Exception.new(1,2,3,4) raise a, “Hello!” and it works all right and I get output: Test.rb:5: Hello! (MYMOD::Exception) However if I try to do the same thing from C with: VALUE oException, argv[4]={INT2FIX(1), INT2FIX(2), INT2FIX(3), INT2FIX(4)}; oException = rb\_class\_new\_instance(4, argv, xr\_cException); rb\_raise(oException, “Hello!”); I put this piece of code inside a method named raiseit and call test from a test ruby program. I get error: Test.rb:9:in `raiseit': undefined method`new’ for #\ (NoMethodError) It seems that when I try to create an object of type MYMOD::Exception, somehow ruby doesn’t find the new method. I’ve tried to define also a new method for this class, but I get the same error. By the way, the function rb\_call\_new\_instance seems to be quite undocumented… What is the correct way to create a new object of a given class from C? Thanks libit ---
**Author:** ![libit](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/8baadc/32.png) [@libit](https://www.ruby-forum.com/u/libit)\ **Post date:** [October 19, 2007, 6:23pm UTC](https://www.ruby-forum.com/t/extendig-ruby-defining-classes-and-creating-objects-from-c/117716/2 "2007-10-19T18:23:48Z")
Hi, At Sat, 20 Oct 2007 00:56:16 +0900, An Onymous wrote in [ruby-talk:274836]: > rb\_raise(oException, “Hello!”); The first argument of rb\_raise() is a class. Try: ``` rb_exc_raise(oException); ``` ---
**Author:** ![libit](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/8baadc/32.png) [@libit](https://www.ruby-forum.com/u/libit)\ **Post date:** [October 20, 2007, 1:56am UTC](https://www.ruby-forum.com/t/extendig-ruby-defining-classes-and-creating-objects-from-c/117716/3 "2007-10-20T01:56:18Z")
Hi, At Sat, 20 Oct 2007 04:33:33 +0900, An Onymous wrote in [ruby-talk:274879]: > > ``` > > rb_exc_raise(oException); > > > > ``` > > rb\_exc\_raise is not defined in ruby.h. At least not in the latest > version 1.8.6 It’s declared in intern.h which is included by ruby.h. > What is it? I see it defined in intern.h and called from everywhere but > I can’t find where it is defined. In eval.c. ---
**Author:** ![libit](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/8baadc/32.png) [@libit](https://www.ruby-forum.com/u/libit)\ **Post date:** [October 20, 2007, 5:40am UTC](https://www.ruby-forum.com/t/extendig-ruby-defining-classes-and-creating-objects-from-c/117716/4 "2007-10-20T05:40:21Z")
Thank you. Now it works. I ended up writing an updated version of rb\_raise which behaves more like the ruby “raise” global function. That is: myrb\_raise(Qnil,NULL) behaves like “raise” myrb\_raise(Qnil,fmt,…) behaves like "raise " raising a RuntimeError with the given message myrb\_raise(exc,NULL) behaves like "raise " where exc can be either a class OR AN EXCEPTION OBJECT (if exc is an exception object, its message is preserved) and myrb\_raise(exc,fmt,…) behaves like “raise ,” that is like the previous one but also setting the exception message. Here it is: VALUE myrb\_raise(VALUE exc, const char \*fmt, …) { if(!NIL\_P(exc)) { ID exception = rb\_intern(“exception”); if(!rb\_respond\_to(exc, exception)) rb\_raise(rb\_eTypeError, “exception class/object expected”); } if(fmt) { va\_list args; char buf[BUFSIZ]; VALUE msg; va\_init\_list(args,fmt); vsnprintf(buf, BUFSIZ, fmt, args); va\_end(args); msg=rb\_str\_new2(buf); if(NIL\_P(exc)) exc = rb\_class\_new\_instance(1, &msg, rb\_eRuntimeError); else exc = rb\_funcall(exc, exception, 1, msg); } rb\_exc\_raise(exc); } ---
**Author:** ![libit](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/8baadc/32.png) [@libit](https://www.ruby-forum.com/u/libit)\ **Post date:** [October 20, 2007, 5:52am UTC](https://www.ruby-forum.com/t/extendig-ruby-defining-classes-and-creating-objects-from-c/117716/5 "2007-10-20T05:52:29Z")
Actually the first few lines should read: VALUE myrb\_raise(VALUE exc, const char \*fmt, …) { ID exception; if(!NIL\_P(exc)) { exception = rb\_intern(“exception”); … ---
**Author:** ![libit](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/8baadc/32.png) [@libit](https://www.ruby-forum.com/u/libit)\ **Post date:** [October 19, 2007, 9:33pm UTC](https://www.ruby-forum.com/t/extendig-ruby-defining-classes-and-creating-objects-from-c/117716/6 "2007-10-19T21:33:31Z")
Oh, so ruby was looking for a “new” method not on the class but on the instance. This explains the problem, however how do I raise an exception from an object? > ``` > rb_exc_raise(oException); > > ``` rb\_exc\_raise is not defined in ruby.h. At least not in the latest version 1.8.6 What is it? I see it defined in intern.h and called from everywhere but I can’t find where it is defined. libit