vectors of vectors in functions

[marcoP]

Hi there,
I want to pass a matrix as an argument of a function, and instead of using multidimensional arrays or pointers to pointers my teacher told me to use vectors of vectors. the code is something like this:

#include <iostream>
#include <vector>

using namespace std;

void example(vector <vector <double> > &v1, vector <vector <double> > &v2, int N)
{
for(int i = 0; i < N+2; i++)
	{
		for(int j = 0; j < N+2; j++)
		{
			v1[i][j] = 2.0;	
                        v2[i][j] = v1[i][j];	
                }
       }
}

and then on the main function:

int main()
{

int N;
cin >> N;

vector <vector <double> > v1(N+2);    //here I declare the two matrixes
vector <vector <double> > v2(N+2);

example(v1, v2, N);

return 0;
}

but I get the following errors:

referred to line 10 in the main:
error: invalid initialization of reference of type ‘std::vector<std::vector<double, std::allocator<double> >, std::allocator<std::vector<double, std::allocator<double> > > >&’ from expression of type ‘double’

and, referred to line 6 in the first part of the code:
error: in passing argument 2 of ‘void init_guess(std::vector<std::vector<double, std::allocator<double> >, std::allocator<std::vector<double, std::allocator<double> > > >&, std::vector<std::vector<double, std::allocator<double> >, std::allocator<std::vector<double, std::allocator<double> > > >&, int)’

What do these errors mean?

P.S. this is not the whole of my program but it's the part that is giving me errors.

[vlad from moscow]

You should show relevant code. In the error message there is function name void init_guess not void example

[Cubbi]

that compiles fine, but your v1 and v2 are vectors of N+2 empty vectors, and the first v1[i][j] is an error.

Change your v1 and v2 in main to

vector <vector <double> > v1(N+2, vector<double>(N+2) );
vector <vector <double> > v2(N+2, vector<double>(N+2) );

Also, vectors know their size, so passing N to your function is redundant.

[marcoP]

I checked the real code of the program and I only made an error in calling the function..
Thanks!