分段故障过载 (<<)

，所以我正在练习C 的编码，并且我正在尝试编写具有相关超载操作的矩阵（存储为数组）的类。

我已经定义了班级，并试图超负荷＆lt;＆lt;运算符，但我当前的代码正在导致分割故障（i在Ubuntu中使用G 编译）。我在网上看，遇到类似问题的人总是会忘记在其过载功能中返回OS，但是我已经这样做了，所以我不知道我的问题可能是什么。此外，我的超载操作员在导致分割故障之前多次工作。

任何帮助将不胜感激。

这是我的代码：

#include<iostream>
#include<stdlib.h> // for c style exit
using namespace std;
class matrix
{
  // Friends
  friend ostream & operator<<(ostream &os, const matrix &mat);
  friend istream & operator>>(istream &is, matrix &mat);
private:
  double *mdata;
  int rows,columns;
public:
  // Default constructor
  matrix(){mdata=0; rows=columns=0;}
  // Parameterized constructor
  matrix(int m, int n){mdata = new double[ m*n ]; rows = m; columns = n;}
  // Copy constructor
  matrix(matrix &mat)
  // Destructor
  ~matrix(){delete[] mdata; cout<<"Destructing array."<<endl;}
  // Access functions
  int getrows() const {return rows;} // Return number of rows
  int getcols() const {return columns;} // Return number of columns
  int index(int m, int n) const // Return position in array of element (m,n)
  {
    if(m>0 && m<=rows && n>0 && n<=columns) return (n-1)+(m-1)*columns;
    else {cout<<"Error: out of range"<<endl; exit(1);}
  }
  double & operator()(int m, int n)const {return mdata[index(m,n)];}
  // Other access functions go here
  double & operator[](int i) {return mdata[i];}
  // Other functions 
  // Copy  Assignment operator
  matrix & operator=(matrix &mat);
};
// Member functions defined outside class
matrix::matrix(matrix &mat){
  rows = mat.getrows();
  columns = mat.getcols();
  for(int j = 0; j<rows*columns; j++){mdata[j] = mat[j];}
 }
matrix & matrix::operator=(matrix &mat){
  if (&mat == this) return *this;
  delete[] mdata; rows = 0; columns = 0;
  rows = mat.getrows(); columns = mat.getcols();
  if(rows>0&&columns>0){
    mdata = new double[(columns-1) + (rows-1)*columns + 1];
    for(int j = 0; j<rows*columns; j++){mdata[j] = mat[j];}
  }
  return *this;
}

// Overload insertion to output stream for matrices
ostream & operator<<(ostream &os, const matrix &mat){
  for(int j = 0;j<mat.rows;j++){
    for(int k = 0;k<mat.columns;k++){
      os << mat(j+1,k+1) << " ";
   }
    os << endl;
 }
  return os;
}
// Main program
int main(){
  // Demonstrate default constructor
  matrix a1;
  cout<<a1;
  // Parameterized constructor
  const int m(2),n(2);
  matrix a2(m,n);
  // Set values for a2 here
  a2[0] = 1; a2[1] = 2; a2[2] = 3; a2[3] = 4;
  // Print matrix a2
  cout<<a2;

  // Deep copy by assignment: define new matrix a3 then copy from a2 to a3
  matrix a3(m,n);
  cout<<a3;
  a3=a2;
  cout<<a3;
  // Modify contents of original matrix and show assigned matrix is unchanged here
  a2[0] = 5;
  cout<<a2;
  cout<<a3; //here is where segmentation fault occurs
  return 0;
}