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Building an extension in C++

8 Message(s) by 4 Author(s) originally posted in ruby programming


From: Gary Date:   Friday, October 19, 2007
I'm using cygwin to try to build an extension in C++ . I have stripped
down the pickaxe book's example (http://www.rubycentral.com/pickaxe/
ext_ruby.html) to the bare minimum. It looks like:

#include "ruby.h

VALUE cTest;

void Init_Test() {
cTest = rb_define_class("Test", rb_cObject);
}

If I name the file Test.c, it works nicely. If I name the file
Test.cpp I get the following error when I try to require the file in
irb.

LoadError: No such file or directory - /usr/lib/ruby/site_ruby/1.8/
i386-cygwin/Test.so
from /usr/lib/ruby/site_ruby/1.8/i386-cygwin/Text.so
from (irb):1

For the whole proceedure I do:

make clean
ruby extconf.rb
make
make install
irb
require "Test"

Any helpful ideas?


From: MenTaLguY Date:   Friday, October 19, 2007
wrote in message :
I'm using cygwin to try to build an extension in C++. I have stripped
down the pickaxe book's example (http://www.rubycentral.com/pickaxe/
ext_ruby.html) to the bare minimum. It looks like:
#include "ruby.h
VALUE cTest;
void Init_Test() {
cTest = rb_define_class("Test", rb_cObject);
}



Although it isn't the source of the problem with the shared object
not being found, you need to declare Init_Test with C linkage
(extern "C"), or else Ruby won't be able to find the entry point.

Besides this, though, safe handling of C++ and Ruby exception s is
extremely difficult when writing an extension in C++. You should
probably consider writing the Ruby-facing portion of extension in
C, with a C-linkage int erface to the C++ portion of the extension,
and be sure to intercept any C++ exceptions before they can cross
into C or Ruby and create havoc. Similarly, C++ code shouldn't
raise Ruby exceptions or call anything which could raise them.

-mental


From: Gary Date:   Saturday, October 20, 2007
Thank you mental!!! It works. I should've figured it out myself,
but I needed your help.

I'm I bit confused about a C-linkage interface to the C++ portion. Is
this going to be more than wrapping the C++ calls in try catch(...)
In other words having something like

extern "C" VALUE t_init(VALUE self)
{
//declare any Ruby C++ data conversion vars in C
try
{
//call C++ functions
}
catch(...)
{
//process exceptions
}
//Do any data interactions between C++ and Ruby
}

Once again, thanks! I spent several hours stumped.

-Gary

wrote in message:
wrote in message:
> I'm using cygwin to try to build an extension in C++. I have stripped
> down the pickaxe book's example (http://www.rubycentral.com/pickaxe/
> ext_ruby.html) to the bare minimum. It looks like:
> #include "ruby.h
> VALUE cTest;
> void Init_Test() {
> cTest = rb_define_class("Test", rb_cObject);
> }
Although it isn't the source of the problem with the shared object
not being found, you need to declare Init_Test with C linkage
(extern "C"), or else Ruby won't be able to find the entry point.
Besides this, though, safe handling of C++ and Ruby exceptions is
extremely difficult when writing an extension in C++. You should
probably consider writing the Ruby-facing portion of extension in
C, with a C-linkage interface to the C++ portion of the extension,
and be sure to intercept any C++ exceptions before they can cross
into C or Ruby and create havoc. Similarly, C++ code shouldn't
raise Ruby exceptions or call anything which could raise them.


> -mental


From: Robert Klemme Date:   Saturday, October 20, 2007
wrote in message:
Thank you mental!!! It works. I should've figured it out myself,
but I needed your help.
I'm I bit confused about a C-linkage interface to the C++ portion. Is
this going to be more than wrapping the C++ calls in try catch(...)
In other words having something like
extern "C" VALUE t_init(VALUE self)
{
//declare any Ruby C++ data conversion vars in C
try
{
//call C++ functions
}
catch(...)
{
//process exceptions
}
//Do any data interactions between C++ and Ruby
}
Once again, thanks! I spent several hours stumped.



That'll probably suffice. You might get a bit better results by
catching explicit exception type s and converting them to Ruby world
exceptions. Other than that your code should prevent any havoc caused
by C++ exceptions raised into the Ruby interpreter.

Kind regards

robert


From: Gary Date:   Saturday, October 20, 2007
Thank you Robert! I agree and understand about catching and
converting C++ exceptions to Ruby exceptions.

Now, on to my next problem. When I try using new I get linker errors
(grrr)

extern "C" void Init_Test() {
cTest = rb_define_class("Test", rb_cObject);

try
{
int *x=new int;
}
catch (...)
{
}
}

I get the following errors:

undefined reference to '___gxx_personality_sj0'
undefined reference to 'operator new(unsigned int)
undefined reference to '___cxa_begine_catch'
undefined reference to '___cxa_end_catch'

It compiles nicely if I replace:
int *x=new int;
with
int *x=NULL

-Gary

wrote in message:
wrote in message:
> Thank you mental!!! It works. I should've figured it out myself,
> but I needed your help.
> I'm I bit confused about a C-linkage interface to the C++ portion. Is
> this going to be more than wrapping the C++ calls in try catch(...)
> In other words having something like
> extern "C" VALUE t_init(VALUE self)
> {
> //declare any Ruby C++ data conversion vars in C
> try
> {
> //call C++ functions
> }
> catch(...)
> {
> //process exceptions
> }
> //Do any data interactions between C++ and Ruby
> }
> Once again, thanks! I spent several hours stumped.
That'll probably suffice. You might get a bit better results by
catching explicit exception types and converting them to Ruby world
exceptions. Other than that your code should prevent any havoc caused
by C++ exceptions raised into the Ruby interpreter.
Kind regards


> robert


From: Paul Brannan Date:   Wednesday, October 24, 2007
wrote in message:
Now, on to my next problem. When I try using new I get linker errors
(grrr)



Are you compiling with gcc or g++?

Paul


From: Gary Date:   Friday, October 26, 2007
wrote in message:
wrote in message:
> Now, on to my next problem. When I try using new I get linker errors
> (grrr)
Are you compiling with gcc or g++?
Paul



When I type make the line says

g++ (blah blah blah)

Although when I look at the Makefile it has the following line:

CC = gcc

If it is any help, my extconf.rb is as follows:

require 'mkmf'
create_makefile ("Test")

I hope I have given you as much information as you need, and perhaps
more =-)

Thank you Paul


From: Gary Date:   Sunday, October 28, 2007
Thank you Nobu!!! Your a genius!

This cleared up the last of my problems! Wheee!!!!

-Gar

wrote in message:
Hi,
At Sat, 27 Oct 2007 06:25:00 +0900,
wrote in message in [ruby-talk:276038]:
> Although when I look at the Makefile it has the following line:
> CC = gcc
mkmf.rb in 1.8 does not support C++.
Perhaps make has default macro CXX and a rule for C++. But C++ runtime
library is not linked by default using gcc, you will need to add the
library in extconf.rb explicitly, like as:
have_library("stdc++")
--
Nobu Nakada






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