从 C++ 调用 Fortran 有多“昂贵”？

Question

I'm writting a program in C++ that calls some functions I had written in Fortran. I was going to test a very basic example in which I call a function called toRadians from the C++ code:

real function toRadian(degree)
  implicit none

  real, intent(in) :: degree
  real :: radians

  radians = (degree*PI)/180
  return
end function toRadian

And so I wonder, is this "worth it"? When I finish the whole thing that function will be called within Fortran where the bulk of the computations will be done, but doing this basic example got me thinking about if, for a simple computation like this, is calling the Fortran function more expensive than just having that function in C++?

Sorry for my ignorance I'm not very sure about how the linking between these compiled codes works. (I'm also very new with Fortran so if you want to make any remark about the previous function please go ahead).

Thanks for your time and have a nice day.

Answer 1

Calling a Fortran function is as cheap as calling another C++ function. Usually.

The problem is the compatibility between the two languages. The best way to start this in Fortran is to use iso_c_binding so that the function has a C calling convention.

Then the other issue is that both languages require their own runtime libraries, and there are no linker flag to use both. So the usual practice is to create a shared library for the Fortran code and link it against the C++ application (and vice-versa when it's calling C++ from Fortran).