Create a 2d vector of pair ints

[DrJones]

How would i create a 2d vector of pair of ints, and how do i iterate through the positions?

[anup30]

struct T
{ 
	int n1;
	int n2;
};

int main()
{
	T a{5,6};
	
	cout << a.n1 << " " << a.n2 << endl;
	
	vector<T> vect;	
	vect.push_back(a);

return 0;
}

[DrJones]

I hoped for something like vector<vector<pair<int,int>>>

or is it not possible?

[keskiverto]

Yes, it is possible. However, do note that
vector<vector<pair<int,int>>> foo;
the foo is empty. You could push_pack one or more vector<pair<int,int>> "rows" into it (and fill each row separately).

If you want a "neat" rectangle, then:

size_t rows = ...
size_t cols = ...
vector<vector<pair<int,int>>> foo( rows, vector<pair<int,int>>( cols ) );

Iteration is a nested loop. There are many styles for that.

[DrJones]

How do i then insert a pair?

[anup30]

// store object in vector
#include <iostream>
#include <vector>
using namespace std;

class Pair {
public:
	int x;
	int y;
	Pair() { x=0, y=0;  }
	Pair(int n1, int n2) { x=n1; y=n2;  }
		
};

int main()
{	
	int row= 3, column= 5;
	Pair x(5,6); // x Pair object
	
	vector<Pair> ar;
	vector<vector<Pair> > arr;
	
	for (int i=0; i<row; i++)
	{
		arr.push_back(ar);
	}
	
	
	for (int i=0; i<row; i++)
	{
		for(int j=0; j<column; j++)
		{
			arr[i].push_back( Pair(i,j) );
		}
	}
	
	cout << arr[2][3].x << ", " << arr[2][3].y; // 2, 3
	
	return 0;
}

[DrJones]

vector<vector<pair<int,int>>> temp (1000, vector<pair<int, int>>(1000));
vector<vector<Test>> temp (1000, vector<Test>(1000));

I have this class, and a vector of vector of this class which i am having some problems with, inserting object of this class into the vector..

class Test{
public:
    Test(vector<vector<pair<int, int>>> &temp)
   { 
     Objects = move(temp);
    };
    vector<vector<pair<int, int>>> Objects;
};

vector<vector<pair<int,int>>> temp (1000, vector<pair<int, int>>(1000));
vector<vector<Test>> objects_vector (1000, vector<Test>(1000));


//for loop inserting elements to temp
objects_vector(temp); // gives me an error message saying this constructor doesn't exist.. 

[anup30]

// 2D vector, objects, pair
#include <iostream>
#include <vector>
#include <utility> // pair()
using namespace std;

class Test{
public:
    vector<vector<pair<int, int>>> Obj;    
    Test () { }    
	Test (vector<vector<pair<int, int> > > temp)
	{ 
		Obj = temp; //move(temp);
	}
};


int main() {
	
	std::pair <int,int> foo;
	foo = std::make_pair (10,20);
	cout << "foo: " << foo.first << ", " << foo.second << '\n';

	vector<pair<int,int> > v1;	
	
	vector<vector<pair<int,int> > > v2;
	
	for (int row=0; row<10; row++) {
		v2.push_back( v1 );
		for (int column=0; column<5; column++) {
			v2[row].push_back( std::make_pair (row,column) );
		}
		
	}	
	cout << v2.at(9).at(4).first << " " <<  v2.at(9).at(4).second << "\n";
	
	cout << "\n";
	
	Test t1;
	Test t2(v2);
	vector<Test> vt(100, v2);
	cout << vt[99].Obj[6][3].first << " " <<  vt[99].Obj[6][3].second << "\n";	

return 0;	
}

[keskiverto]

class Test{
public:
    vector<vector<pair<int, int>>> Objects;
};

vector<vector<Test>> foo;

That is a bit scary, because it is almost the same as:
vector<vector<vector<vector<pair<int, int>>>>> foo;
A 4D array of pairs.

How do i then insert a pair?

size_t rows = ...
size_t cols = ...
vector<vector<pair<int,int>>> bar( rows, vector<pair<int,int>>( cols ) );
// the bar does already have rows*cols pairs.  One has to simply change their values.
for ( size_t row = 0; row < bar.size(); ++row {
  for ( size_t col = 0; col < bar[row].size(); ++col ) {
    // some "real" data
    bar[row][col].first = 42 + row;
    bar[row][col].second = col - 7;
  }
}

objects_vector(temp); // gives me an error message saying this constructor doesn't exist..

One element (value_type) in your objects_vector is a vector<Test>. The temp is a vector<vector<pair<int,int>>>. Its value_type is vector<pair<int,int>>.

The std::vector has 6 constructor forms: http://www.cplusplus.com/reference/vector/vector/vector/
None of those matches to your case.