打印时 c++ 中的二维矢量出现问题

Question

class Vertex {
    public:
    int dist, num;
    vector<Vertex*> edges;
    Vertex() {}
    Vertex(int num) : num(num) {}
};
class K {
public:
    void updateMatrix(vector<vector<int>>& matrix) {
        vector<vector<Vertex>> vec;
        for (vector<int> in : matrix) { 
            vector<Vertex> neu;
            vec.push_back(neu);
            for (int i : in) {
                Vertex k(i);
                cout << k.num;
                neu.push_back(k);
            }
        }
        for (vector<Vertex> in : vec) {
            for (Vertex i : in) cout << i.num << " ";
            cout << endl;
        }
    }
};

When I call the function with a valid 2D vector, when I try to print vec the output is just 3 blank lines. How can I fix this?

Answer 1

vec.push_back(neu); puts a copy of the (empty) variable neu into vec . Changes to neu after this don't affect the copy.

You should move that to after the inner loop.