从对象打印二维矢量时出错

您好！我正在制作一个矩阵类，应该打印出矩阵的函数破坏了程序。我确信这个逻辑是正确的，所以我可能在某个地方犯了一个愚蠢的错误。问题是，我好像找不到它。

这是整个搜索代码：

#include <iostream>
#include <vector>
using namespace std;

class Matrix{
    private:
    double determinant;
   vector<vector <int> > body;
    int ROWS;
    int COLUMNS;
    public:
    int get_rows(){return ROWS;}
    int get_columns(){return COLUMNS;}
    vector<vector <int> > get_body(){return body;}
    //default constructor
    Matrix();
    //set up constructor
    Matrix(int rows, int columns);
};
//creates the matrix and let's the user fill it's value
Matrix :: Matrix(int ROWS, int COLUMNS){
     vector< vector<int> > body;
    this->ROWS = ROWS;
    this->COLUMNS = COLUMNS;
     for(int i = 0; i < ROWS; i++){
        cout<<"Row " << i << " begins" <<endl;
        vector<int> tmp;
        for(int z = 0; z < COLUMNS; z++){
            cout<<"Column "<< z<< " begins."<<endl;
            int temp;
            cin >> temp;
            tmp.push_back(temp);
        }
        body.push_back(tmp);
    }
}
//default constructor
Matrix:: Matrix(){
     vector< vector<int> > body;
}
void  print(Matrix a){
    for(int i = 0; i < a.get_rows(); i++){
        for(int z = 0; z < a.get_columns(); z++){
            cout<<a.get_body()[i][z];
        }
        cout<< endl;
    }
}
int main()
{
    Matrix a(2, 2);
    print(a);
    return 0;
}

而被破坏的功能体：

void  print(Matrix a){
    for(int i = 0; i < a.get_rows(); i++){
        for(int z = 0; z < a.get_columns(); z++){
            cout<<a.get_body()[i][z];
        }
        cout<< endl;
    }
}