Declaring Dynamic 2D Vector in class

Question

We\'re trying to use a 2D vector because we want a 2D array that will grow dynamically.

We tried this: In the class declaration:

    vector

        

Answer 1

You can access the element in [][] manner by derefrencing.

Vector<vector<double>> *table ;
table = new vector<vector<double>> ( n, vector<double>( m, 0.0)) ;
cout << (*table)[i][j] ;

Most of the times, this works perfectly well.

Answer 2

Make sure your vectors are large enough to store your elements. If a vector t has size N, the last element you can access is t[N-1].

t = vector<vector<double> > (10, vector<double>(10));
t[50] = vector<double>(5); // This is wrong! Vector size is 10, you access 50th.
t[50][10] = 10; // Wrong again! Vector size 5, you access 10th.

Answer 3

If you have Boost installed try using Boost Multi-array.

Answer 4

You'll need to resize the tables before you access elements.

vector<vector<double> > table;
table.resize(10);
for (int i = 0; i < 10; ++i)
  table[i].resize(20);