如何访问（例如，cout）多维 STL 向量中的迭代器的当前值（C++）

Question

I'm still very much a neophyte in using STL. The following code fragment populates a 3D vector (S) and compiles (g++) fine.

const int maxBonds = 6;
vector< vector< vector<int> > > S;
S.resize(maxBonds);
populate(S); // function that returns S with various layers filled with int data in rows and columns.
for (vector<vector<vector<int> > >::iterator Slayer = S.begin(); Slayer != S.end(); Slayer++) {
    cout << "Layer contains " << Slayer->size() << " rows" << endl;
    for (vector<vector<int> >::iterator Srow = Slayer->begin(); Srow != Slayer->end(); Srow++) {
        for (vector<int>::iterator Scol = Srow->begin(); Scol != Srow->end(); Scol++) {
            cout << *Scol;
        }
        cout << endl;
    }
    cout << endl;
}

This runs fine:

Layer contains 0 rows

Layer contains 5 rows
000
200
020
220
002

Layer contains 12 rows
100
010
210
... // etc.

However, I'd like to print out the value of the outer iterators (Slayer, Srow) during iteration. How do I properly dereference the current value of Slayer, ie

 cout << "Layer # " << Slayer->??? << " contains " << Slayer->size() << " rows" << endl;

Answer 1

If what you need is the current vector "index", i think that the standard way to do this is to increment another value.

unsigned int countSlayer = 0;

for (vector<vector<vector<int> > >::iterator Slayer = S.begin(); Slayer != S.end(); Slayer++, ++countSlayer) {

    cout << "Layer # " << countSlayer << " contains " << Slayer->size() << " rows" << endl;

    for (vector<vector<int> >::iterator Srow = Slayer->begin(); Srow != Slayer->end(); Srow++) {
        for (vector<int>::iterator Scol = Srow->begin(); Scol != Srow->end(); Scol++) {
            cout << *Scol;
        }
        cout << endl;
    }
    cout << endl;
}

You can also try to subtract begin() from the iterator but it doesn't work well with all iterators types (I lack time for making some tests).

Answer 2

You can't do this directly.

The way I'd do it - define an function with a loop to do this for you.

---

Something like:

void Print2dIntVector( const vector<vector<int> >& v )
{
    // ..
}
void Print3dIntVector( const vector< vector< vector<int> > >& v )
{
    // ..
}

Advice - use typedef , instead of writing all these long, nested vectors.

EDIT : Of cource, you can always overload operator<< for these types (vectors)

Answer 3

So *Scol gets you the int within the last vector, *Srow would get you the vector of the row, *Slayer would get you the vector of the layers containing the vector of rows.