R CHECK issue on CRAN related to C++ complex numbers

Question

I'm doing a package using 'Rcpp' and it contains this function:

Eigen::MatrixXcd matricesToMatrixXcd(const Eigen::MatrixXd& Re,
                                     const Eigen::MatrixXd& Im) {
  return Re.cast<std::complex<double>>() + 1i * Im.cast<std::complex<double>>();
}

Here, 1i is the unit imaginary number.

I submitted the package to CRAN but the R CHECK on Debian generates this warning:

* checking whether package ‘EigenR’ can be installed ... [297s/297s] WARNING
Found the following significant warnings:
  EigenR.cpp:10:44: warning: imaginary constants are a GCC extension

Would you know what should I do?

Answer 1

Yeah, this has worked:

Eigen::MatrixXcd matricesToMatrixXcd(const Eigen::MatrixXd& Re,
                                     const Eigen::MatrixXd& Im) {
  const std::complex<double> I_ {0.0, 1.0};
  return Re.cast<std::complex<double>>() + I_ * Im.cast<std::complex<double>>();
}