C++ generic type of generic type

Question

I'm trying to build a generic matrix based on a generic vector that I've already built. I want to have a vector of vectors (each internal vector represents a row). For some reason, this isn't working:

template <typename T>
class matrix : vector<vector<T>>{...}

I'm getting this error:

error: 'class vector<T>' is not a valid type for a template non-type parameter

I tried looking into template templates, but couldn't really understand how to make them work. Any help would be much appreciated. Thanks!

Answer 1

This should work for you:

#include <vector>

template <typename T>
class matrix : public std::vector<std::vector<T>>
{
};

int main()
{
    matrix<int> m;

    m.push_back({});
    m[0].push_back(0);
    m[0].push_back(1);
    m[0].push_back(2);

    m.push_back({});
    m[1].push_back(3);
    m[1].push_back(4);
    m[1].push_back(5);

    m.push_back({});
    m[2].push_back(6);
    m[2].push_back(7);
    m[2].push_back(8);

    return 0;
}

However I suggest investigating "A proper way to create a matrix in c++" topic which looks very close to what your want to implement.