Re: Type conversion function for user type again.

From:

=?iso-8859-1?q?Erik_Wikstr=F6m?= <eriwik@student.chalmers.se>

Newsgroups:

comp.lang.c++

Date:

18 May 2007 00:10:00 -0700

Message-ID:

<1179472200.520426.56630@q75g2000hsh.googlegroups.com>

On 18 Maj, 03:03, zaemi...@gmail.com wrote:

I got a good answer here I have still confusing part.

I have two very simple classes

class DRect
{
    private :
       double x0, y0, x1, y1;
    public :
        DRect(double a, double b, double c, double d) : x0(a), y0(b),
x1(c), y1(d) {}
        void Union(const DRect* p)
        {
            x0 = MIN(x0, p->x0);
            y0 = MIN(y0, p->y0);
            x1 = MAX(x1, p->x1);
            y1 = MAX(y1, p->y1);
        }

};

class IRect
{
    private :
       int x0, y0, x1, y1;
    public :
       IRect(int a, int b, int c, int d) : x0(a), y0(b), x1(c), y1(d)
{}
       operator DRect() const
       {
           return DRect(x0, y0, x1, y1);
       }
       operator DRect*() const
       {
           return &DRect(x0, y0, x1, y1);
       }

};

and the execution code here.

void main()
{
    DRect d(5.3, 5.3, 15.6, 15.6);
    IRect i(10, 10, 100, 100);

    /* 1. No problem with compiling this code. */
    d.Union(&(static_cast<DRect>(i)));

    /* 2. It isn't compiled. */
    d.Union(&i);

}

Use references instead, pointers should normally not be used unless
you have to.

#include <iostream>

class DRect {
private :
  double x0, y0, x1, y1;
public :
  DRect(double a, double b, double c, double d)
    : x0(a), y0(b), x1(c), y1(d) {}

  void Union(const DRect& p) {
    std::cout << "Union";
  }
};

class IRect {
private :
  int x0, y0, x1, y1;
public :
  IRect(int a, int b, int c, int d)
    : x0(a), y0(b), x1(c), y1(d) {}

  operator DRect() const {
    return DRect(x0, y0, x1, y1);
  }
};

int main() { // Notice int and not void as return-type
  DRect d(5.3, 5.3, 15.6, 15.6);
  IRect i(10, 10, 100, 100);
  d.Union(i);
}

--
Erik Wikstr=F6m