c - 如何将外部类型的参数从 C 传递到 Fortran

Question

假设我在 Fortran 中有以下子例程

    subroutine exec(routine)        implicit none        external     :: routine        real(kind=8) :: res        call routine(2.0d0, res)        print *, "Fortran Result: res = ", res    end subroutine exec

该子例程接收外部例程作为参数。现在，假设该例程是用 C 编写的，并且我还需要从 C 调用 Fortran 例程 exec。就像这样:

    void op(double x, double *f) {        *f = pow(x, 2);    }    void main() {        exec_(op);    }

我知道，如果我不传递外部子例程而是传递整数、 double 或其他常规类型，那么它会起作用，但此代码会返回段错误。有没有办法将 external 类型的参数从 C 传递到 Fortran？

Answer 1

这有效，您必须使用指针:

void op(double *x, double *f) {
    *f = pow(*x, 2);
}

void main() {
    exec_(&op);
}

subroutine exec(routine)

    implicit none

    external     :: routine
    real(kind(1.d0)) :: res

    call routine(2.0d0, res)
    print *, "Fortran Result: res = ", res

end subroutine exec

不要使用 kind=8 它不声明 8 字节实数，而是声明类型编号为 8 的处理器相关类型。即使是旧的非标准 real*8 也会变得更好。

但最好使用 Fortran 2003 c 互操作性和 iso_c_binding 模块:

f.f90

subroutine exec(routine_c) bind(C,name="exec_") use iso_c_binding implicit none

    abstract interface
        subroutine sub(a,b) bind(C)
          use iso_c_binding
          implicit none
          real(c_double),value :: a
          real(c_double) :: b
        end subroutine
    end interface

type(c_funptr),value :: routine_c
real(c_double) :: res
procedure(sub),pointer :: routine

call c_f_procpointer(routine_c,routine)

call routine(2.0d0, res)
print *, "Fortran Result: res = ", res

end subroutine exec

抄送

#include <math.h>
void op(double x, double *f) {
    *f = pow(x, 2.0);
}

int main() {
    extern void exec_(void (*) (double, double *));
    exec_(&op);
    return 0;
}

编译:

 gfortran c.c f.f90 -Wall -g -fbacktrace -fcheck=all
cc1: warning: command line option ‘-fbacktrace’ is valid for Fortran but not for C [enabled by default]
cc1: warning: command line option ‘-fcheck=all’ is valid for Fortran but not for C [enabled by default]
 ./a.out 
 Fortran Result: res =    4.0000000000000000