vector<vector<T> > ?

vector<vector<T> > is kinda like 2D, right? How would I insert something to it? I know how to do it with vector<T> but my brains seem to sprain when figuring this one out (perhaps 'cause this was the very first day when I did something with STL).

You could do something like -

Code:

---

#include <iostream>
#include <vector>

using namespace std;


int main ( void )
{
        vector<vector<int> > i;

        vector <int> temp1;
        temp1.push_back(1);
        temp1.push_back(2);
        vector <int> temp2;
        temp2.push_back(3);
        temp2.push_back(4);

        i.push_back(temp1);
        i.push_back(temp2);

        cout << i[0][0] << i[0][1] << i[1][0] << i[1][1];
       
       
        return 0;

}

---

This is probably clearer, as long as you note that the inner vectors are limited to a size of 20 -

Code:

---

#include <iostream>
#include <vector>

using namespace std;


int main ( void )
{
        vector<vector<int> > i;

        vector <int> temp1(20);
        i.push_back(temp1);
        i.push_back(temp1);
        i[0][0] = 1;
        i[0][1] = 2;
        i[1][0] = 3;
        i[1][1] = 4;



        cout << i[0][0] << i[0][1] << i[1][0] << i[1][1];


       
       
        return 0;

}

---

Although you could resize the inner vectors doing -

i[0].resize(30);

or dynamically push elements on the back using

i[0].push_back(21);

which would then be accessed like -

cout << i[0][20];

Just what I figured out an hour later after posting... :-) But, what I was after was how to do it without that temp variable; is it possible to hardcode that temp1 in?

Code:

---

#include <vector>

using std::vector;

int main() {
    int width = 10;
    int height = 10;

    // Create a vector of width vectors of height ints
    vector<vector<int> > vecvec(width, vector<int>(height));
}

---

Note that moving a vector is expensive so compound containers will be quite inefficent (the STL thinks of a move as a copy followed by the destruction of the source, see Typed Buffers at www.moderncppdesign.com for a workaround).

Ummm, I have never seen that syntax before: vector<vector<int>> i
What does it do? Whats the differens from int i[?][?]?