Creating and Using a 2 dimensional Vector (vector of vectors)

[xytor]

I am having trouble understanding how to create a 2 dimentional vector (a vector of vectors) and have it act like I want it to.

void test2dVector(){
 vector <vector <int> > v; //*two dimensions
 v.push_back(vector <int>()); //*create v[0]
 v.push_back(vector <int>()); //*create v[1]
 v[0].push_back(15); //*assign v[0][0]
 v[1].push_back(16); //*assign v[1][0]


	    for(size_t i=0;i<v.size();i++)
  {
   for (size_t j=0;j<v[i].size();j++)
   {
       cout<<v[i][j]<<" "; //I am not sure that this will work! Will it?
}
   cout<<"\n";
}



}

In this code, I try to create and use a 2-d vector.
I still do not understand how to make it act like a real 2-d array, meaning, creating an actual grid-like structure, as opposed to this, which only covers one column.

So once and for all, can somebody FULLY explain how to do this, completely?

[Valmont]

Nothing beats some code. and besides, you should check out:
C++ Multi Dimensional Array using Vectors.

#include <iostream>
#include <vector>
#include <cstdlib>

using std::size_t;
using std::vector;
int main()
{  
  vector<vector<int> > Matrix;
  
  //Create the 2x2 matrix.
  size_t rows = 2;
  size_t cols = 2;  
  // 1: set the number of rows.
  Matrix.resize(rows);
  // 2: set the number of columns per row.
  for(size_t i = 0; i < rows; ++i)
  {
    Matrix[i].resize(cols);
  }
  
  Matrix[0][0] = 1;
  Matrix[0][1] = 2;
  Matrix[1][0] = 3;
  Matrix[1][1] = 4;
  
  //Demo of row/column workings.
  for(size_t i = 0; i < rows; ++i)
  {
    for(size_t j = 0; j < cols; ++j)
    {
      std::cout <<"["<<i<<"]"<<"["<<j<<"] = " <<Matrix[i][j]<<std::endl;
    }
  }  
  
  return 0;
}

[xytor]

OOh, so the resize function of the vector is needed.
Thats what I didn't know.
Thank you so much!!