From: Gareth Reeves <reevesg@...>
Date: 2006-03-10T00:48:44+09:00
Subject: c++ extension

I am trying to understand some aspects of writing a ruby extension in 
C++.

Actually what I am trying to do is wrap a C++ library and make it 
accessible from ruby. Since I have been having problems with the library 
that I am trying to wrap, I decided to create a really simple library 
and try wrapping that.

The biggest problem that I am having is understanding scope. When I 
create the wrapper for the class I create a new instance of the class 
that I am wrapping and store it in a ptr. Then when I want to access 
methods of this class the wrapper class just delegates to the ptr. 
Simple stuff.

When I use a regular ptr things mostly work OK except that I can only 
create one instance of the class.

The library I am trying to wrap uses smart pointers, so I created a 
version of my code that uses simple pointers. The problem that I have 
hear is that these objects then fall out of scope and the destructors 
get called immediately after wrapper class method exists. The result of 
course is that I get segmentation faults or weird results.

I have only a little experience in C++ and this is my first extension 
that I have written.

How should I go about wrapping these c++ classes?

Thanks in advance.

Here is the code....
//extension.cpp
#include <ruby.h>
#include <test.h>
#include <smartptr.h>

typedef VALUE (ruby_method)(...);

auto_ptr<Test> test;
//test* test;

extern "C" VALUE t_TEST_init(VALUE self, VALUE value )
{
        Param * param = new Param( NUM2INT( value ) );
        test = auto_ptr<Test>( new Test( param ) );
        //test = new Test( param );
        return self;
}

extern "C" VALUE t_TEST_value(VALUE self)
{
        return INT2NUM( test->ParamValue() );
}

auto_ptr<Param> param;
//Param* param;

extern "C" VALUE t_PARAM_init(VALUE self, VALUE value )
{
        param = auto_ptr<Param>( new Param( 7 ) );
        //param = new Param( NUM2INT( value ) );
        return self;
}

extern "C" VALUE t_PARAM_value(VALUE self)
{
        return INT2NUM( param->value() );
}


VALUE cTest;
VALUE cParam;

extern "C" void Init_Extension()
{
        cTest = rb_define_class( "Test", rb_cObject );
        rb_define_method( cTest, "initialize", (ruby_method*) 
&t_TEST_init, 1 );
        rb_define_method( cTest, "value", (ruby_method*) &t_TEST_value, 
0 );

        cParam = rb_define_class( "Param", rb_cObject );
        rb_define_method( cParam, "initialize", (ruby_method*) 
&t_PARAM_init, 1 );
        rb_define_method( cParam, "value", (ruby_method*) 
&t_PARAM_value, 0 );
}

//test.h
#include <param.h>

class Test {

public:
        Test(Param *);
        ~Test();
        int ParamValue();
private:
        Param *param;

};

//param.h
class Param {

public:
        Param(int);
        ~Param();
        int value();
private:
        int internal;

};

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