一元减运算符重载 C++ 分段错误

Question

I have an object Matrix and I overloaded the unary minus operator and I can't manage to make my program work. If I put the return type as reference it does not allow me to return the object I created inside the function, if I put the return type as Matrix then I get segmentation fault.

in the H file :

Matrix operator - () const; 

in the cpp file:

Matrix Matrix::operator - () const
{
  if (isValid==false)//just a validity check
    return *this;

  Matrix mat(*this);//copy ctor

  for (int i=0;i<row;i++)
       for (int j=0;j<col;j++)
          mat.matrix[i][j]=-matrix[i][j];

  return mat;
}

I tried many permutations of that (adding const, adding by reference) and nothing seems to work. How do I fix this ?

Answer 1

What follows works without any segmentation faults. You should minimize your code by removing anything unneccessary, then gradually transform it to the code below, and see at what stage your segmentation fault vanishes.

#include <iostream>
#include <vector>

using namespace std;

class Matrix {
public:
    Matrix() : isValid(true), row(0), col(0) {}
    Matrix(int r, int c, int val);
    Matrix(const Matrix&);
    Matrix operator - () const; 
private:
    bool isValid;
    int row, col;
    vector<vector<int> > matrix;
};

Matrix::Matrix(int r, int c, int val) : isValid(true), row(r), col(c) {
    matrix.resize(r);
    for (int i=0; i<r; i++)
        matrix[i].resize(c, val);
}

Matrix::Matrix(const Matrix& m) : isValid(true), row(m.row), col(m.col), matrix(m.matrix) {}

Matrix Matrix::operator - () const
{
  if (isValid==false)//just a validity check
    return *this;

  Matrix mat(*this);//copy ctor

  for (int i=0;i<row;i++)
       for (int j=0;j<col;j++)
          mat.matrix[i][j]=-matrix[i][j];

  return mat;
}

main() {
    int r=10, c=5;
    Matrix m(r, c, 1);
    Matrix m1;
    m1 = -m;
}