CODEWITHSUNDEEP
c++eigeneigen3
hamster on wheels
hamster on wheels

Reputation: 2893

Have a class with an Eigen::matrix attribute that maps to a std::vector attribute

I want class Test to have a Eigen::Matrix that maps to Test::_a. This means whenever I change the std::vector, the Eigen::Matrix would also immediately reflect the change because both the vector and the matrix uses the same chunk of memory to hold data.

This works:

#include <Eigen/Dense>
#include <vector>
int main() {
    std::vector<int> a;
    a.resize(10);
    typedef Eigen::Matrix<int, 1, Eigen::Dynamic>  mat_type;
    Eigen::Map< mat_type > a_eigen(a.data(), a.size());
}

But this doesn't work....

#include <Eigen/Dense>
#include <vector>
class Test {
public:
    Test(int size) {
        _a.resize(size);
        _a_eigen(_a.data(), size );
    }
    std::vector<int> _a;
    Eigen::Map< Eigen::Matrix<int, 1, Eigen::Dynamic> > _a_eigen;
};
int main() {
    Test t(10);
}

Below also doesn't work because cout prints nothing

#include <Eigen/Dense>
#include <vector>
#include <iostream>
class Test {
public:
    typedef Eigen::Matrix<int, 1, Eigen::Dynamic> mat_type;
    Test(int size) {
        _a.resize(size);
        Eigen::Map<mat_type>(_a_eigen) = Eigen::Map<mat_type>(_a.data(), size );
        for (int i = 0; i < size; ++i) _a[i] = i;
    }
    std::vector<int> _a;
    mat_type _a_eigen;
};
int main() {
    Test t(10);
    std::cout << t._a_eigen;
}

Upvotes: 2

Views: 1069

Answers (1)

chtz
chtz

Reputation: 18817

You need to initialize the Map in the initializer-list of your class' constructor:

#include <Eigen/Core>
#include <vector>
class Test {
public:
    Test(int size) : _a(size), _a_eigen(_a.data(), size) { }
    std::vector<int> _a;
    Eigen::Map< Eigen::Matrix<int, 1, Eigen::Dynamic> > _a_eigen;
};

Upvotes: 4

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