通过调用Fortran中的C ++函数将Fortran int数组传递给C ++ [英] Passing a Fortran int array to C++ by calling C++ function in Fortran

问题描述

我想在Fortran子程序中调用C ++函数。这个C ++函数应该更新一个整数数组。这里是我写的一个非工作代码。问题是什么？

 ！ Fortran函数调用C ++函数。 
 
子例程my_function（）
 
整数（4）ar（*）
 
整数（4）get_filled_ar 
 
！此处需要正确的语法。 
 ar = get_filled_ar（）
 end 
 
 
 // C ++函数：
 
 externC{
 void get_filled_ar （int * ar）{
 ar [0] = 1; 
 ar [1] = 10; 
 ar [3] = 100; 
} 
} 
  

解决方案

Fortran 2003有一个标准，从而平台和编译器独立的方式调用C从Fortran，以及任何使用C调用接口的语言。同样从C调用Fortran。虽然各种编译器编写器逐渐增加Fortran 2003功能，并且几乎没有完整的2003编译器，ISO C Binding已经在许多编译器中可用了一段时间。 ISO C Binding比以前的临时技术更好，这些技术有时记录不良，并且在编译器和平台之间有所不同。要从Fortran调用C，你写一个接口告诉Fortran编译器它应该使用C调用约定和C类型。

这是一个例子。正如Mike写的，由于C ++函数返回void，在Fortran中将其作为子例程并调用它。因此，它不需要给一个类型。另外，在Fortran的某个地方，你必须为数组预留存储空间 - 最简单的方法是使用带有数值的声明。

 程序test_call_C 
 
使用iso_c_binding 
 
 implicit none 
 
 interface c_interface 
 
子程序get_filled_ar（ar）bind（C，name =get_filled_ar）
 
使用iso_c_binding 
 
 implicit none 
 
 integer（c_int），intent（out），dimension（*）:: ar 
 
 end子程序get_filled_ar 
 
 end interface c_interface 
 
 
整数（c_int），维度（0：3）:: ar 
 
调用get_filled_ar（ar）
 b $ b write（*，*）Fortran：ar：，ar 
 
 stop 
 
结束程序test_call_C 
  pre> 
 
 
和C：
  void get_filled_ar b int ar [] 
）{
 
 ar [0] = 1; 
 ar [1] = 10; 
 ar [2] = 100; 
 
 return; 
 
} 
  
示例命令：
  gcc -c get_filled_ar.c 
 gfortran get_filled_ar.o test_call_C.f90 -o test_call_C.exe 
 ./test_call_C.exe 
  
要调用您的C ++代码，请使用以下命令。 
  g ++ -c cplusplus在绑定中指定的名称不需要尾随下划线.cc 
 gfortran cplusplus.o test_call_C.f90 -o test_call_Cplusplus.exe 
 ./test_call_Cplusplus.exe 
  
 
I am trying to call a C++ function in a Fortran subroutine. This C++ function is supposed to update an integer array. Here is a non-working code I wrote. What is the issue?
! Fortran function that calls a C++ function.

subroutine my_function()

      integer(4) ar(*)

      integer(4) get_filled_ar

      ! Need correct syntax here.
      ar = get_filled_ar()
end


// C++ function:

    extern "C" {
        void get_filled_ar(int *ar){
            ar[0] = 1;
            ar[1] = 10;
            ar[3] = 100;
        }
    }

解决方案
With Fortran 2003 there is a standard and thus platform and compiler independent way to call C from Fortran, and also any language that uses the C calling interface.    Also to call Fortran from C.  While the various compiler writers are gradually adding Fortran 2003 features and there are few complete 2003 compilers, the ISO C Binding has been available for some time in many compilers.  The ISO C Binding works better than the previous ad hoc techniques, which were sometimes poorly documented, and varied between compilers and platforms. To call C from Fortran, you write an "interface" that tells the Fortran compiler that it should use the C calling conventions, and C types.    

Here is an example.   As Mike wrote, since the C++ function returns void, treat it in the Fortran as a subroutine and call it.   Thus it doesn't need to be given a type.   Also, somewhere in the Fortran you have to reserve storage for the array -- the easiest way is with a declaration with numeric value for the dimension.   And you need a main program in some language.
program test_call_C

use iso_c_binding

implicit none

interface c_interface

   subroutine get_filled_ar (ar) bind (C, name = "get_filled_ar")

   use iso_c_binding

   implicit none

   integer (c_int), intent (out), dimension (*) :: ar

   end subroutine get_filled_ar

end interface c_interface


integer (c_int), dimension (0:3) :: ar

call get_filled_ar (ar)

write (*, *) "Fortran: ar:", ar

stop

end program test_call_C
and in C:
void get_filled_ar (
   int ar []
) {

   ar [0] = 1;
   ar [1] = 10;
   ar [2] = 100;

   return;

}
Example commands:
gcc -c get_filled_ar.c
gfortran get_filled_ar.o test_call_C.f90  -o test_call_C.exe
./test_call_C.exe
To call your C++ code, use the following commands.  The name specified in the "bind" obviates the need for a trailing underscore so your C++ code works directly.
g++ -c cplusplus.cc
gfortran cplusplus.o test_call_C.f90  -o test_call_Cplusplus.exe
./test_call_Cplusplus.exe


                        
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