Copy on write (COW) smart pointers

[thecount]

What implemetation for a copy on write pointer do you recommend that I use, since it's not a completely standard thing? I found the link to http://code.axter.com/cow_ptr.h, used it, and it crashed. I am compiling with visual studio v8.0 without a glitch and I am starting to think I just didn't understand how to use the pointer. Below, I attach a simple program that crashed, but works fine with a copy pointer from http://code.axter.com/copy_ptr.h. Thanks a lot in advance for your help

[thecount]

Sorry and don't accuse me of flooding. I realized there was an error in my sample code -- I had been trying things out and I happen to send the wrong version (although it also crashes, even doing yet less than the one below). It should return

point[0] = ( 0 , 0 )
point[1] = ( 1 , 0 )
point[0] = ( 0 , 0 )
point[1] = ( 1 , 0 )
copypoint[0] = ( 49 , 0 )
copypoint[1] = ( 1 , 0 )

but the input is

/*   CLASS    */
class point2D
{
protected:
    double x_,y_;
public:
    point2D() : x_(0), y_(0) {}
    point2D(double x, double y) : x_(x), y_(y) {}
    void setx(double x) { x_ = x;}
    void sety(double y) { y_ = y;}
    double getx() const { return x_;}
    double gety() const { return y_;}
};
 
class point3D : public point2D
{
private:
    double z_;
public:
    point3D() : point2D(), z_(0) {}
    point3D(double x, double y, double z) : point2D(x,y), z_(z) {}
    void setz(double z) { z_ = z;}
    double getz() const { return z_;}
};
 

and the main

    std::size_t npoints = 2;
    std::vector<cow_ptr<point2D> > points(npoints);
 
    // initialize 
 
    for(std::size_t i = 0; i < npoints; ++i)
    {
        points[i] = cow_ptr<point2D>(new point3D(i,0,i+1));
    }
 
    // first print to check input
 
    for(std::size_t i = 0; i < points.size(); ++i)
    {
        std::cout << "point[" << i << "] = ( " 
            << points[i]->getx() << " , " 
            << points[i]->gety() << " )" 
            << std::endl;
    }
 
    // copy vector and make changes
 
    std::vector<cow_ptr<point2D> > copypoints = points;
    copypoints[0]->setx(49.0);
 
    // check that old vector and new vector are not shared
 
    for(std::size_t i = 0; i < points.size(); ++i)
    {
        std::cout << "point[" << i << "] = ( " 
            << points[i]->getx() << " , " 
            << points[i]->gety() << " )" 
            << std::endl;
    }
    for(std::size_t i = 0; i < copypoints.size(); ++i)
    {
        std::cout << "copypoint[" << i << "] = ( " 
            << copypoints[i]->getx() << " , " << 
            copypoints[i]->gety() << " )" << 
            std::endl;
    }
 

Sorry about that

[weaknessforcats]

You might read the article in the C/C++ HowTos about Handle Classes. That article contains a template for a smart pointer that does what you want.

[thecount]

Thanks a lot for the answer. I'll try it right away and let you know if it works. Regards