how to create a contiguous 2d array in c++?

Question

I want to create a function that returns a contiguous 2D array in C++.

It is not a problem to create the array using the command:

 int (*v)[cols] = n         


        

Answer 1

handling raw memory ressources is often icky. Best shot is a simple wrapper as :

struct array2D : private std::vector
{
  typedef  std::vector base_type;

  array2D() : base_type(), height_(0), width_(0) {}
  array2D(std::size_t h, std::size_t w) : base_type(h*w), height_(h), width_(w);

  int operator()(std::size_t i, std::size_t j) const 
  { 
     return base_type::operator[](i+j*height_); 
  }

  int& operator()(std::size_t i, std::size_t j) 
  { 
     return base_type::operator[](i+j*height_); 
  }

  std::size_t rows() const { return height_; }
  std::size_t cols() const { return width_; }

  private:
  std::size_t height_, width_;
}

private inheritance let you grab all the goodies from vector, just add your 2D constructor. Ressources management is free as vector ctor/dtor will do their magic. Obviously, the i+h*j can be changed to whateever storage order you want.

vector< vector< int > > is 2D but won't be contiguous in memory.

Your function then become :

array2D create_array(int rows, int cols)
{
  return array2D(cols,rows);
}

EDIT:

You can also retrieve other vector interface parts like begin/end or size with the usign clause to make the private inherited member functions public again.