I have a class member variable "M" of type Eigen::Matrix<float,4,4,Eigen::RowMajor> that I'd like to initialize to the values in a multidimensional array parameter "matrix" in the initialization list of the class constructor. It appears the constructor for Matrix only takes 1D arrays, not multidimensional arrays. From what I understand elements of a multidimensional array are stored sequentially in row-major order in memory and multidimensional arrays are pointers to an array. So, I do not understand why M( &matrix[0][0] ) does not work. By not work, I mean the array values are not all correct (corrupt).

Thanks,
Ryan

Please show how 'matrix' has been declared. If you have "float **matrix;", then that cannot work while a "float matrix[4][4]" should be OK.

Thanks for the reply. It is declared like the following:

typedef Eigen::Matrix<float,4,4,Eigen::RowMajor> mat44f;
class B : public A
{
public:

B( const float matrix[4][4] ) : M( &matrix[0][0] ) { }

protected:

mat44f M;
};

It appears some elements are correct while some are corrupt. The following works without issue:

B( const float matrix[4][4] )
{
for (int i = 0; i < 4; i++) for (int j = 0; j < 4; j++)
{
M( i, j ) = matrix[i][j];
}
}

Ryan

I cannot reproduce the issue. The following is working fine:

Code: Select all

#include <Eigen/Core>
#include <iostream>
using namespace Eigen;
int main()
{
  float m[4][4] = {{1, 2, 3, 4}, {5, 6, 7, 8}, { 9, 10, 11, 12}, {13, 14, 15, 16}};
  typedef Matrix<float,4,4,RowMajor> Mat44;
  std::cout << Map<Mat44>(&m[0][0]) << "\n\n" << Mat44(&m[0][0]) << "\n\n";
}


I think this may be an issue of copying the values verse storing a reference to the 4x4 array. I get the 4X4 array from another library. It is stored in a local variable on the stack. I pass a reference to this 4x4 array to the Matrix constructor. I need to make sure the values are copied as the reference to the array is no longer valid once it goes out of scope. I suspect the Matrix constructor does not copy the value, rather it just stores the reference. I heard Eigen uses expression templates. If that is the case, a copy is not made until it is deemed necessary, right? I believe your example works because your 4x4 array does not got out of scope before you print.

Ryan

The Map<> construct stores only a reference, however, the Mat44 constructor does perform a deep copy of the values. You might run your program under valgrind to check memory issues.