Re: Multidimensional array member initialization

From:

"io_x" <a@b.c.invalid>

Newsgroups:

comp.lang.c++

Date:

Sat, 9 Jan 2010 22:28:19 +0100

Message-ID:

<4b48f314$0$1110$4fafbaef@reader2.news.tin.it>

----------
"Gert-Jan de Vos" <gert-jan.de.vos@onsneteindhoven.nl> ha scritto nel messaggio
news:4a41375a-4445-4ffb-bf67-ebd403d600fe@j5g2000yqm.googlegroups.com...

Hope this helps.

Gert-Jan

#include <vector>
etc
---------

i have copy above code adding only some macro,
add 3 "_" in the constructor Image(int, int),
and the main() function for debug.

not understand why img.width()
is called each cicle of the inner loop; why not use
just x<img.width_?

yes i not have understood all but seems to me there
is something wrong g[768][1024].b
not seg fault, so for me could be something wrong.

than for me the centre of the exercise is:
immage has to be one big array without holes in it.
Can some of you could say "vector" operate in one big array
without holes in it?
-----------------------
#include <iostream>
#include <cstdlib>
#include <stdint.h>
#include <vector>

using namespace std;

template <typename T>
class Image
{
    class Indexer
    {
    public:
        Indexer(T* data) : data_(data)
        {
        }

        T& operator[](int x) const
        {
            return data_[x];
        }

    private:
        T* data_;
    };

    class ConstIndexer
    {
    public:
        ConstIndexer(const T* data) : data_(data)
        {
        }

        T operator[](int x) const
        {
            return data_[x];
        }

    private:
        const T* data_;
    };

public:
    Image(int width, int height) :
        width_(width),
        height_(height),
        data_(width*height)
    {
    }

    int width() const
    {
        return width_;
    }

    int height() const
    {
        return height_;
    }

    Indexer operator[](int y)
    {
        return Indexer(&data_[y*width_]);
    }

    ConstIndexer operator[](int y) const
    {
        return ConstIndexer(&data_[y*width_]);
    }

private:
    int width_;
    int height_;
    std::vector<T> data_;
};

struct Color3d
{
    double r, g, b;
};

void fill(Image<Color3d>& img, Color3d color)
{
    for (int y = 0; y < img.height(); ++y)
        for (int x = 0; x < img.width(); ++x)
            img[y][x] = color;
}

int main(void)
{Color3d h={0.78373, 0.1383, 1-0.78373-0.1383};
Image<Color3d> g(768, 1024);

cout << "Inizio\n";

fill(g, h);
cout << "(r,g,b)==(" << g[0][0].r << ", "
                      << g[0][0].g << ", "
                      << g[768][1024].b << ")\n";
cout << "end\n";
return 0;
}
---------
this below is the rewrite of above in one readable form;
with the same error, in one inesistent position of the array
the [768][124] say the same value of all other (1-0.78373-0.1383)
and not seg fault.

instead my example seg fault if [768][1024]; it
return 0 [and not (1-0.78373-0.1383)] for [767][1024]
better!
---------
#include <iostream>
#include <cstdlib>
#include <stdint.h>
#include <vector>

using namespace std;

template <typename T> class Image{
public:
int width_;
int height_;
std::vector<T> data;

  class Indexer{
  public:
  T* data;
  Indexer(T* dat) : data(dat){}
  T& operator[](int x){return data[x];}
  };

  Image(int w, int h): width_(w), height_(h), data(w*h){}

  int width() {return width_;}
  int height() {return height_;}

  // img[y] is Indexer
  // where is the memory of Indexr? It is created and destroy?
  // img[y][x] is T&
  Indexer operator[](int y)
    {return Indexer( & data[y*width_] );}
};

struct Color3d{
  double r, g, b;
};

void fill(Image<Color3d>& img, Color3d& color)
{for (int y=0; y<img.height_; ++y)
    for (int x=0; x<img.width_; ++x)
            img[y][x]=color;
}

int main(void)
{Color3d h={0.78373, 0.1383, 1-0.78373-0.1383};
Image<Color3d> g(768, 1024);

cout << "Inizio\n";

fill(g, h);
cout << "(r,g,b)==(" << g[0][0].r << ", "
                      << g[0][0].g << ", "
                      << g[768][1024].b << ")\n";
cout << "end\n";
return 0;
}