vectors and inheritance in C++

[sulthana]

Hi,
I was trying to use inheritance to make the existing std::vector to a two dimensional vector.Here is the code below.
#include "stdafx.h"
#include<vector>
#include<iostream>
using namespace std;
//TwoDVector.h
class TwoDVector:public vector<char>
{
public:
TwoDVector(int x,int y);
const int xDimension;
const int yDimension;
vector<char> TwoD;
char get(int x,int y);
void put(int x,int y,char c);
};
//TwoDVector.cpp
#include "stdafx.h"
#include<vector>
#include "TwoDVector.h"
#include<iostream>
using namespace std;

//TwoDVector class

TwoDVector::TwoDVector(int x,int y): xDimension(x),yDimension(y),twoD(xDimension*yDimension)
{
for(int i= 0;i<xDimension*yDimension;i++)
{
twoD[i] = ' ';
}

}
char TwoDVector::get(int row,int col)
{
return(twoD[row*xDimension+col]);
}

void TwoDVector::put(int row,int col,char value)
{
twoD[row*xDimension + col] = value;
}

But I am getting the following errors.Please Could someone help?
1>Compiling...
1>TwoDVector.cpp
1>.\TwoDVector.cpp(10) : error C2614: 'TwoDVector' : illegal member initialization: 'twoD' is not a base or member
1>.\TwoDVector.cpp(13) : error C2065: 'twoD' : undeclared identifier
1>.\TwoDVector.cpp(19) : error C2065: 'twoD' : undeclared identifier
1>.\TwoDVector.cpp(24) : error C2065: 'twoD' : undeclared identifier

[Disch]

Since none of vector's members are virutal (not even its destructor), you're better off not derviing from vector. You could probably hack together something that works, but it would be a lot of effort and would undoubtedly behave strangely if used a certain way (I've tried deriving from STL classes before -- it's not fun or easy).

Instead, you can make your own class which 'has-a' vector, and simply interfaces outside of it.

class vector2d
{
public:
  // get/set stuff here

protected:
  vector<int>  thevectortouse;
};

Of course instead of using int like I do here (and like you did in your example), you could make this a template class:

template <typename T>
class vector2d
{
  //...
  vector<T>  thevectortouse;
};

[PanGalactic]

What makes you think std::vector can or should be subclassed? (Hint: Containers are not designed to be subclassed. You can tell by the lack of a virtual destructor.)

typedef std::vector<std::vector> 2dVector;

And then create a factory function to make constructing them easier.

[sulthana]

To Disch
Thanks for the reply.
Even though I removed the :vector from the two dimensional vector still I am getting the same errors.Could you help?

[sulthana]

sorry! It was a typo.