EIGEN_USE_LAPACKE + MSVC and _Complex

Hello,

I'm using Eigen with -DEIGEN_USE_LAPACKE on Windows with Visual Studio 2017.

As is documented here:

https://docs.microsoft.com/en-us/cpp/c-runtime-library/complex-math-support?view=vs-2019

the Microsoft C-compiler does not support _Complex, but this header in Eigen

https://eigen.tuxfamily.org/dox/lapacke_8h_source.html#l00060

relies on _Complex when you define -DEIGEN_USE_LAPACKE

What is the recommended way to handle this?

For me, adding -Dlapack_complex_float="std::complex<float>" seems to work fine, but it seems strange to use C++ types in an extern C context.

Any comments are welcome.

Tom