Re: Converting an array to a multidimensional one

Salt_Peter <>
Tue, 18 Nov 2008 20:10:15 -0800 (PST)
On Nov 18, 9:14 pm, Slain <> wrote:

I need to convert a an array to a multidimensional one. Since I need
to wrok with existing code, I need to modify a declaration which looks
like this

In the .h file
int *x;

in a initialize function:
x = new int[$Row_Length];

Now I need the x to be able to point to a multidimensional array
I would ahve been fine, with something like
int (*x)[Column_Length] = new int [Row_Length][Column_Length];

But since my variable x needs to be declated in the header file, I am
having some problems compiling. Can some one explain me how to declare
and initialize?

Thank you

Use a vector of vectors instead, much easier and it brings many
dividends (its dynamic, easy to extend - like providing iterators to
the interface). Instead of dealing with heap allocated pointers that
blindly point to whatever in an exception-unsafe way, deal with
objects instead.

// array2d.h, missing include guard

#include <vector>

class Array2D
  typedef std::vector< int > VecN;
  // members
  std::vector< VecN > m_vvn; // 2D array
  // ctors
  Array2D(std::size_t, std::size_t);
  Array2D(std::size_t, std::size_t, const int);
  // member functions
  std::size_t size() const { return m_vvn.size(); }
  VecN operator[](std::size_t index) { return m_vvn[index]; }
  void display() const;

// array2d.cpp

#include <iostream>
#include <algorithm>
#include <iterator>
#include "array2d.h"

Array2D::Array2D(std::size_t rows, std::size_t cols)
: m_vvn(rows, std::vector< int >(cols)) { }

Array2D::Array2D(std::size_t rows, std::size_t cols, const int n)
: m_vvn(rows, std::vector< int >(cols, n)) { }

void Array2D::display() const
  typedef std::vector< VecN >::const_iterator VIter;
  for(VIter it = m_vvn.begin(); it != m_vvn.end(); ++it)
    std::copy( (*it).begin(),
               std::ostream_iterator< int >(std::cout, " ") );
    std::cout << std::endl;

// main.cpp
#include "array2d.h"

int main()
  Array2D a2d(4, 4, 99);
  std::cout << "rows: " << a2d.size() << std::endl;
  std::cout << "columns: " << a2d[0].size() << std::endl;

rows: 4
columns: 4
99 99 99 99
99 99 99 99
99 99 99 99
99 99 99 99

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