Class template with multi-dimensional std::vectors

I am trying to initialize a Matrix-class template, that takes a 2D-vector of any type as a parameter input:

#include <iostream>
#include <vector>

template <class T>
class Matrix 
{
    std::vector<std::vector<T>> entries;

public:
    // Constructor with parameters
    Matrix(std::vector<std::vector<T>> Entries) { 
        entries = Entries;
    }
};

int main() 
{
    std::vector<std::vector<double>> current_entries = { 
        {1, 2, 3}, {-4, 3, 6}, {-7, 8, 9}
    };
    Matrix<std::vector<std::vector<double>>> M1(current_entries); // line 19
    return 0;
}

But this gives the error at line 19:

error: no matching function for call to 
'Matrix<std::vector<std::vector<double> > >::Matrix(std::vector<std::vector<double> >&)'

I suspect it has something to do with the type being a std::vector, because when I replace all the 2D-vectors with ints, without changing anything else it works:

#include <iostream>
#include <vector>

template <class T>
class Matrix 
{
    T entries;

public:
    // Constructor with parameters
    Matrix(T Entries) { 
        entries = Entries;
    }
};

int main() 
{
    double current_entries = 3;
    Matrix<double> M1(current_entries); // line 19
    return 0;
}

>I suspect it has something to do with the type being a vector, [...]

The error has nothing to do with the type being std::vector, rather you are instantiating the class with the wrong type.

Your class template argument at the line

Matrix<std::vector<std::vector<double>>> M1(current_entries);
//     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^  --> is the "T"

is std::vector<std::vector<double>>, not double. Therefore, you instantiate a Matrix with entries of the following type:

 std::vector<std::vector< std::vector<std::vector<double>> >>    entries;
 //                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ----> "T"

Obviously, this is not what you want. You need just Matrix<double>, by which the entries will be with the type std::vector<std::vector<double>>.

Reason for error is already explained in comments. T=vector<vector<float>> will expand entries to vector<vector<vector<vector<float>>>> and I believe that is not the outcome you want.

You can keep generic solution as below and then T can be your desired matrix

#include <iostream>
#include <vector>

template <class T>
class Matrix{
    T entries;
    public:
    Matrix(T Entries) { // Constructor with parameters
      entries = Entries;
    }

};

using namespace std;

int main()
{
    std::cout << "Lets's Start...." << std::endl;
    std::vector<std::vector<double>> current_entries ={{1, 2, 3}, {-4, 3, 6}, {-7, 8, 9}};
    Matrix<std::vector<std::vector<double>>> M1(current_entries); // line 19
    std::cout << "All is well " << std::endl;
    return 0;
}

Alternatively you can also have Template Partial Specialisation for vector<vector<T>> and a separate implementation can be provided as below.

#include <iostream>
#include <vector>

template <class T>
class Matrix {
    T entries;

public:
    Matrix(T Entries) : entries(Entries) {
        // Constructor with parameters
    }
};

// Partial specialization for std::vector<std::vector<T>>
// It should always be implemented after above template
template <class T>
class Matrix<std::vector<std::vector<T>>> {
    std::vector<std::vector<T>> entries;

public:
    Matrix(std::vector<std::vector<T>> Entries) : entries(Entries) {
        // Constructor with parameters
    }
};

int main() {
    std::cout << "Let's Start...." << std::endl;
    std::vector<std::vector<double>> current_entries = {{1, 2, 3}, {-4, 3, 6}, {-7, 8, 9}};
    Matrix<std::vector<std::vector<double>>> M1(current_entries);
    std::cout << "All is well " << std::endl;
    return 0;
}

Hope this helps. If you need more description about any of the solution, please ask in a comment.