Re: new vs. vector vs. array

From:

"Daniel T." <daniel_t@earthlink.net>

Newsgroups:

comp.lang.c++

Date:

Fri, 24 Apr 2009 07:21:06 -0400

Message-ID:

<daniel_t-9B1362.07210624042009@earthlink.vsrv-sjc.supernews.net>

"Mark S." <markstar.n0spam@hotmail.com> wrote:

The problem is that I don't know how to deal with multidimensional
vectors or arrays. I was thinking of using a single vector which is n*n
big. Of course, I would have to convert the numbers then (eg. for 3*3,
[1][1] would become [3]). Moreover, this solution does not seem very
elegant to me.

So, what would you recommend? An array of pointers to the elements? A
vector of pointers? Or a vector of the elements themselves?

Use this, or something like it:

   template<typename?T>
class?Matrix?{
public:
   Matrix(unsigned?nrows,?unsigned?ncols);
?
???//?Access?methods?to?get?the?(i,j)?element:
???T& operator()?(unsigned?i,?unsigned?j);
???const?T&?operator()?(unsigned?i,?unsigned?j)?const;
?
?private:
???unsigned?ncols;
???unsigned?nrows;
   vector<T> data;
?};
?
   template<typename?T>
inline?T&?Matrix<T>::operator()?(unsigned?row,?unsigned?col)
{
   assert(row < nrows);
   assert(col < ncols);
   return?data[row * ncols?+?col];
}

   template<typename?T>
inline?const?T&?Matrix<T>::operator()?(unsigned?row,?unsigned?col)?const
{
   assert(row < nrows);
   assert(col < ncols);
???return?data[row * ncols?+?col];
}
?
   template<typename?T>
Matrix<T>::Matrix(unsigned?nrows,?unsigned?ncols)
      :?nrows(nrows)
      ,?ncols(ncols)
      ,?data(nrows * ncols)
{
   assert(nrows > 0);
   assert(ncols > 0);
}