Re: new vs. vector vs. array
SG wrote:
On 24 Apr., 10:26, "Mark S." <markstar.n0s...@hotmail.com> wrote:
Hi,
even though I'm still at the beginning of my learning process, I am
anxious to program something "real". So I would like to write a little
program to solve Sudokus with variable dimensions (n*n). I think I have
a pretty good idea about the algorithm, but since you guys here strongly
suggested to avoid new & delete as much as possible, I was wondering how
you would suggest how I store the classes:
I'd probably build a class for managing a dynamic 2D array first.
Something like this
template<typename T>
class vector2d
{
std::vector<T> elements;
//...
public:
array2d(int rows, int cols, T const& fill = T());
int rows() const;
int cols() const;
T const& operator()(int r, int c) const;
T & operator()(int r, int c);
};
Hmm, maybe it was too early for me to start this after all. I have not
learned what templates are yet and have no idea what it is you wrote.
Right now I'm at chapter 8 in TICPP (
http://www.linuxtopia.org/online_books/programming_books/thinking_in_c++/index.html
) and templates are discussed in chapter 16. Of course after your post I
read it anyways, though I still don't really understand what is going on
there. :-(
I assume that <typename T> means that T will be replaced (with int,
float, etc), eg. vector<T> becomes <vector<int>.
But I still can't make sense of the rest, in particular
array2d(int rows, int cols, T const& fill = T());
....
T const& operator()(int r, int c) const;
T & operator()(int r, int c);
And I also have no idea how I would actually put this to use. As I said,
maybe I'm not ready yet, though I had really hoped to make this work
with the knowledge I had so far.
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.
Why not?
Well, it means I have to spend a lot of extra time to calculate which
parts of the array I actually want to read/write. That sounds very
inefficient to me.
So, what would you recommend?
An array of pointers to the elements?
No. I would not recommend that. You'd need to explicitly provide a
destructor for cleaning up which also implies the need for user-
defined or explicitly disabled copy and assignment operations (see C++
"rule of three").
A vector of pointers?
No. I would not recommend that for the same reasons as above.
Really? But I was told that vector is better than new/delete. I googled
"rule of three", but must say that I also don't understand what this has
to do with my example (even though the concept itself seems reasonable
and important in general).