如何使用初始化列表 c++ 将元素放入嵌套向量中

Question

I have a Matrix class which contains a vector inside a vector as data within it. I would like to be able to insert elements through initializer lists.

An example of this would be the following:

#include <vector>
int main(void) {
    std::vector<std::vector<int>> v = {
        { 1, 2, 3, 4, 5 },
        { 6, 7, 8, 9, 10 }
    };
}

It should also be noted that the vectors that I am using within the Matrix class are a custom vector class that I have written. I have found a way to use initializer lists to add elements to the vector, but I do not know how to do the same with nested initializer lists, since the initializer lists do not provide subscripts.

I know the size of the outer initializer list (in the above example it is two), but I don't know how to get the size of the second initializer list.

Here is a snippet of my code so far.

Matrix.h

template<class type>
class Matrix {
    private:
        Vector<Vector<type>> data;

    public:
        Matrix() {}
        Matrix(std::initializer_list<std::initializer_list<type>> init_list) {
            /* Get the data */
        }
        
}

Moreover, how does the std::vector class take in a potentially infinite amount of initializer lists and sort them out?

Answer 1

I would like to be able to insert elements through initializer lists. ...I know the size of the outer initializer list (in the above example it is two), but I don't know how to get the size of the second initializer list.

Perhaps I misunderstand you, but the code snippet below should give you a start. It prints the sizes of the outer and inner initializer lists, along with the elements, and compiles and runs fine in C++11, according to clang++ anyway.

// ...
    Matrix(const std::initializer_list<const std::initializer_list<type>> & init_list) {
        cout << "vector of " << init_list.size() << " vectors" << endl;
        for (const auto & inner_list : init_list) {
           cout << inner_list.size() << " elements: " << endl;
           for (const auto & m : inner_list) {
              cout << m << ",";
           }
           cout << endl;
        }
    }

// ...

Matrix<int> M { { 1, 2 }, { -1, 2 } };

Moreover, how does the std::vector class take in a potentially infinite amount of initializer lists and sort them out?

I'm not sure I understand what you mean here. If I understand the question, then I think the snippet above answers it. If I don't, please elaborate in the comments & I can try to address it.