CODEWITHSUNDEEP
c++typeseigen
yannick
yannick

Reputation: 397

eigen matrix const type

consider the following test

Eigen::MatrixXd B(Eigen::MatrixXd::Random(5,5));
const Eigen::MatrixXd C(Eigen::MatrixXd::Random(5,5));
std::cout << "B " << typeid(B).name() << std::endl;
std::cout << "C " << typeid(C).name() << std::endl;
std::cout << " === " << std::endl;
std::cout << "B.T " << typeid(B.transpose()).name() << std::endl;
std::cout << "C.T " << typeid(C.transpose()).name() << std::endl;

and its output

B N5Eigen6MatrixIdLin1ELin1ELi0ELin1ELin1EEE
C N5Eigen6MatrixIdLin1ELin1ELi0ELin1ELin1EEE
 === 
B.T N5Eigen9TransposeINS_6MatrixIdLin1ELin1ELi0ELin1ELin1EEEEE
C.T N5Eigen9TransposeIKNS_6MatrixIdLin1ELin1ELi0ELin1ELin1EEEEE

demangled

B Eigen::Matrix<double, -1, -1, 0, -1, -1>
C Eigen::Matrix<double, -1, -1, 0, -1, -1>
 === 
B.T Eigen::Transpose<Eigen::Matrix<double, -1, -1, 0, -1, -1> >
C.T Eigen::Transpose<Eigen::Matrix<double, -1, -1, 0, -1, -1> const>

Why is C not shown as const? How does Eigen figure out it is? Is this an Eigen issue or is this typeid ?

Upvotes: 1

Views: 408

Answers (1)

Joseph Mansfield
Joseph Mansfield

Reputation: 110658

This is due to the behaviour of typeid:

§5.2.8/5 [expr.typeid] The top-level cv-qualifiers of the glvalue expression or the type-id that is the operand of typeid are always ignored.

So in both cases, the typeid will only apply to Eigen::MatrixXd.

Upvotes: 2

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