C++ vector > reserve size at beginning

Question

in c++ I have

vector > table;

How can I resize vector so that it has 3 rows and 4 columns, all zeros?

Someth

Answer 1

Don't! You'll have complex code and rubbish memory locality.

Instead have a vector of twelve integers, wrapped by a class that converts 2D indices into 1D indices.

template
struct matrix
{
   matrix(unsigned m, unsigned n)
     : m(m)
     , n(n)
     , vs(m*n)
   {}

   T& operator()(unsigned i, unsigned j)
   {
      return vs[i + m * j];
   }

private:
   unsigned m;
   unsigned n;
   std::vector vs;
};

int main()
{
   matrix m(3, 4);   // <-- there's your initialisation
   m(1, 1) = 3;
}