Getting and setting a three dimensional array - c++

Question

I have to get a three dimensional array c[] w[] h[] from a class and convert it into a single dimensional array of unsigned char[]. I tried this way. But it doesnt work !!.. When I give the input through command line the execution halts and breaks...
Implementation:
#include <iostream>
#include<fstream>
#include<stdlib.h>
#include<vector>
//#include "E:\Marvin_To_UnsignedChar\MetisImg.hpp"
//#include "C:\Users\padmanab\Documents\Visual Studio 2013\Projects\Marvin_To_UnsignedChar\MetisImg.hpp"
extern "C"
{
#include "C:\Users\padmanab\Desktop\Marvin_To_UnsignedChar\multiplyImage\multiplyImage.h"
//#include "C:\Users\padmanab\Documents\Visual Studio 2013\Projects\Marvin_To_UnsignedChar\multiplyImage\multiplyImage.h"
}
using namespace std;
class Marvin_To_UnsignedChar
{
public:
int Color;
int Width;
int Height;
std::vector<unsigned char> values;
Marvin_To_UnsignedChar(int c, int w, int h) : Color(c), Width(w), Height(h), values(c*w*h){}
unsigned char operator()(int color, int width, int height) const
{
return values[Height*Width*color + Height*width + height];
}
unsigned char& operator()(int color, int width, int height)
{
return values[Height*Width*color + Height*width + height];
}
};
In Main():
int color; int width; int height;
std::cout << "Please enter the color value";
std::cin >> color;
std::cout << "Please enter the width value";
std::cin >> width;
std::cout << "Please enter the height value";
std::cin >> height;
Marvin_To_UnsignedChar M_To_V(color,width,height);
unsigned char test = M_To_V(color, width, height);
std::cout << test << '\n';
It would be great to have some guidance about the issue or may be a better method to implement it !

Answer 1

The class code is fine. The problem is that in
unsigned char test = M_To_V(color, width, height);
you are invoking the operator() with the dimensions as parameters (remember that you used before color, width, height to construct the Marvin_To_UnsignedChar object), so it will effectively output values[Color*Width*Height], which is one element past the end of the vector. Otherwise the code is fine, you probably want to use something like
unsigned char test = M_To_V(x, y, z);
where x, y, z are such that x<color, y<width, z<height.
For example, the code below works (I am initializing in the constructor the array with 'x' so you can see that something is printed out)
#include <iostream>
#include <vector>
using namespace std;
class Marvin_To_UnsignedChar
{
public:
int Color;
int Width;
int Height;
std::vector<unsigned char> values;
Marvin_To_UnsignedChar(int c, int w, int h) :
Color(c), Width(w), Height(h), values(c*w*h,'x'){}
unsigned char operator()(int color, int width, int height) const
{
return values.at(Height*Width*color + Height*width + height);
}
unsigned char& operator()(int color, int width, int height)
{
return values.at(Height*Width*color + Height*width + height);
}
};
int main()
{
int color = 3, width = 777, height = 600;
Marvin_To_UnsignedChar M_To_V(color,width,height);
M_To_V(2, 776, 599)='a'; // set the last element to `a`
std::cout << M_To_V(2, 776, 599) << '\n';
unsigned char test = M_To_V(1, 200, 300); // this element is pre-initialized with 'x'
std::cout << test << '\n';
}
PS: you can use values.at(position) instead of values[position] for a std::vector, and the former will check for out of bounds, i.e. throw an exception if you get an out of bound, so you can figure out what's going on. The values[position] form is faster, but I recommend using at at least in debug mode if you are not 100% sure that you may overflow.