Import frontend module procedure from fortran into C
How do I import fortran interface
into C using extern
?
Suppose I have the following fortran module:
!swapper module
module swapper
interface swap
module procedure swap_r, swap_i, swap_c
end interface
contains
!subroutine implementations here:
!swap_r takes two double precision as argument
!swap_i takes two integers as argument
!swap_c takes two characters as argument
end module swapper
Then I can just do in C, the following?
extern "C" void __swapper_MOD_swap(double*, double*)
extern "C" void __swapper_MOD_swap(int*, int*)
extern "C" void __swapper_MOD_swap(char*, char*)
Alternatively, if I promise to swap
only call with double precision numbers, can I do this exclusively?
extern "C" void __swapper_MOD_swap(double*, double*)
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It looks like you are actually using C ++. But first, let's answer in C or C ++ style:
No you can't do
extern "C" void __swapper_MOD_swap(double*, double*)
you cannot do this for three different types of arguments, you cannot even do this for one type of arguments.
In fact, there shouldn't be any __swapper_MOD_swap
in the library.
What Fortran does is that it maintains an interface (which is just a description of how to call something) to three special subroutines swap_r, swap_i, swap_c
and allows you to call it by name swap
.
But there is no real subroutine in the module swap
. Fortran will simply allow you to name these three specifications under a different name, that's all.
It is not possible to call these functions from C as generic. C does not have this kind of generics! (It has some functionality that works with any type using void*
).
In C ++, you can create generics specialized for different types, and you can call Fortran procedures as generic, but you have to tell that to C ++ yourself! You can create a template and manually customize that template to call the appropriate functions extern "C"
.
For an example see my title https://github.com/LadaF/PoisFFT/blob/master/src/poisfft.h where I create a C ++ class that is linked to extern "C" struct
and some extern "C"
functionality that is however implemented in Fortran ...
Finally, DO NOT use symbols __swapper_MOD_
. Create Fortran bindings with bind(C,name="some_name")
and call some_name
through extern "C"
, because different Fortran compilers use different name translation schemes.
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