运算符重载

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

class Matrix
{
public:
    Matrix(){memset(this->_mat,0,sizeof(this->_mat));}
    Matrix(float tmp[4][4] )
    {
          for (int i=0;i<4;i++)
                      for(int j=0;j<4;j++)
                          _mat[i][j]=tmp[i][j];
    }
    Matrix(const Matrix *tmp)
    {
        memcpy(this->_mat,tmp->_mat,sizeof(tmp->_mat));
    }
//    Matrix operator+(Matrix &a,Matrix &b)
//    {
//        Matrix result(a);
//        return result+=b;
//
//    }
   Matrix operator+(Matrix &a)
   {
       Matrix tmp(this);

       tmp+=a;
       return tmp;
   }
  void operator+=(const Matrix &b) const
        {
      for (int i=0;i<4;i++)
                  for(int j=0;j<4;j++)
                      _mat[i][j]+=b._mat[i][j];
        }
    float& operator() (int , int );
    float operator() (int rwo,int colum) const;
    void print() const
    {
        for (int i=0;i<4;i++)
        {
                          for(int j=0;j<4;j++)
                          {
                             cout<<_mat[i][j]<<" ";
                          }
        cout<<endl;
       }
    }
private:
    mutable float _mat[4][4];
};

//float  Matrix::operator ()(int r,int c) const
//{
//    return this->_mat[r][c];
//}
float&  Matrix::operator ()(int r,int c)
{
    return this->_mat[r][c];
}
 
int main()
{ 
    Matrix a,b;
    float tmp[4][4]={{0,1,2,3},{1,2,3,4},{2,3,4,5},{3,4,5,6}};
  Matrix aa(tmp);
  Matrix c(aa);
  c.print();
   cout<<c(1,3);
   c(1,3)=5; cout<<c(1,3)<<endl;
  b.print();
  aa+=aa;
  aa.print();
  a=aa+ b;
  a.print();


}