为什么 uchar* 指向垫子的指针变为空？

Question

为什么在下面的代码中指向 EVectors 和 EValues 的指针无论是在 main 函数还是在 MYLDA 函数中都变为空？以及如何解决？

void main()
    {
      // some code
      Mat EVectors;
      Mat EValues;
      uchar* pEVectors = EVectors.data;
      uchar* pEValues = EValues.data;          
      MYLDA(train_labels, train_data, pEVectors, pEValues);
      // some code
    }

void MYLDA(vector<int> gnd, Mat_<float> _data, uchar* eigvector, uchar* eigvalue)
    {
      // some code
      GeneralizedEigenSolver<MatrixXf> ges;  
      ges.compute(DPrime, WPrime);    
      MatrixXcf eigenvectorsInEigen = ges.eigenvectors();      
      VectorXcf eigenvaluesInEigen = ges.eigenvalues();  
      Mat eigenvectorsOpenCV(eigenvectorsInEigen.rows(), 
      eigenvectorsInEigen.cols(), CV_32FC1, eigenvectorsInEigen.data());
      eigvector = eigenvectorsOpenCV;      
      Mat eigenvaluesOpenCV(eigenvaluesInEigen.rows(), 
      eigenvaluesInEigen.cols(), CV_32FC1, eigenvaluesInEigen.data());
      eigvalue = eigenvaluesOpenCV;   
    }

Answer 1

解决此问题的一种方法是：

    void main()
    {
      // some code
      Mat EVectors;
      Mat EValues;

      MYLDA(train_labels, train_data, &EVectors, &EValues);
      // some code
    }

void MYLDA(vector<int> gnd, Mat_<float> _data, Mat* eigvector, MAt* eigvalue)
    {
      // some code
      *eigvector = eigenvectorsOpenCV;      

      *eigvalue = eigenvaluesOpenCV;   
    }

为什么 uchar* 指向垫子的指针变为空？

why uchar* pointer to a mat become null?

c++

opencv

eigen