STL General: How to declare and use two-dimensional arrays?

[Yves M]

Q: How can I define a dynamic two-dimensional array?

A: The basic idea is to use a 'vector<vector<T> >'. Use containment to write a template class that offers the desired functionality. Following skeleton code shows how to implement and use such a class:

#include <vector>

template <typename T>
class dynamic_array
{
public:
  dynamic_array(){};
  dynamic_array(int rows, int cols)
  {
    for(int i=0; i<rows; ++i)
    {
      data_.push_back(std::vector<T>(cols));
    }
  }
  
  // other ctors ....

  inline std::vector<T> & operator[](int i) { return data_[i]; }

  inline const std::vector<T> & operator[] (int i) const { return data_[i]; }

  // other accessors, like at() ...

  void resize(int rows, int cols)
  {
    data_.resize(rows);
    for(int i = 0; i < rows; ++i)
      data_[i].resize(cols);
  }

  // other member functions, like reserve()....

private:
  std::vector<std::vector<T> > data_;  
};


int main()
{
  dynamic_array<int> a(3, 3);
  a[1][1] = 2;
  int x = a[1][1];
  return 0;
}

A different approach, not using the STL 'vector' class, is shown in the following FAQ...


FAQ contributed by: [Gabriel Fleseriu] [Axter]