Fortran接口以调用返回指向数组的指针的C函数 [英] Fortran interface to call a C function that returns a pointer to an array
问题描述
After much searching, I found what I believe to be the closest answer to my problem is on Stack Overflow (SO) at Fortran interface to call a C function that return a pointer, (posted nearly 10 years ago!)
之所以这样引用，是因为使用该示例可使代码保持简单，并且仍然说明了我的问题.
I quote this because using that example keeps the code simple and still illustrates my problem.
我想返回一个已经在C ++中创建/分配的内存的数组，并且能够在Fortran中分析答案，因为这是此应用程序的大部分代码所在的地方.我的应用程序进入C ++生成整数数组答案，并通过C接口将其返回给Fortran程序.原始的SO示例使用单个双精度变量作为返回值.我将其更改为整数，因为这就是我在应用程序中要处理的内容.示例代码(已更改)有效.
I want to return an array that has been created/memory allocated in C++ and be able to analyse the answer in Fortran, because that is where the bulk of the code for this application lies. My application goes off into C++ to produce the integer array answer and returns it to the Fortran program via the C interface. The original SO example used a single double precision variable as the return. I’ve changed it to integer because that is what I will be dealing with in my application. The example code (as changed) works.
我已在注释中突出显示了为返回数组指针而试图进行的更改，但我的想法已经用完了.(我可以说，哦，在糟糕的过去，我可以将整数等同于iarray(1)并超出数组的大小."但我不会.拥有编码保护是很好的，但是有时真令人沮丧.)
I have highlighted with comments the changes that I have tried to make to return an array pointer, but I’ve run out of ideas. (I could say, "Oh for the bad old days when I could just equivalence an integer to an iarray(1) and go beyond the size of the array", but I won’t. It’s good to have coding protections, but sometimes it gets frustrating.)
我正在使用Visual Studio 2017和Intel Fortran parallel_studio_xe_2019_update5_composer.
I am using Visual Studio 2017 and Intel Fortran parallel_studio_xe_2019_update5_composer.
我修改的原始SO代码示例:
My modified example of the original SO code:
! ps_test_pointers.f90
program foo
use, intrinsic :: iso_c_binding, only : c_ptr, &
c_f_pointer, &
c_int
implicit none
type(c_ptr) :: c_p!(:) ! <-------
integer(c_int), pointer :: f_p!(:) ! <-------
interface
function foofunc() bind(c)
import :: c_ptr
implicit none
type(c_ptr) :: foofunc!(:) ! <-------
end function foofunc
end interface
c_p = foofunc()
call c_f_pointer(c_p, f_p)
print *, f_p
end program foo
// ps_test_pointersC.cpp : 'Subroutine' only.
extern "C" {
int bar[3] = { 2, 3, 4 };
int *foofunc() {
return bar;
}
}
如上所述，该代码有效，因为它可以打印出数组的第一个元素("2").
As I said above, the code works, in the sense that it prints out the first element of the array (‘2’).
如果我在f_p的定义中添加'(:)'，则代码将正确编译，但是当我运行它时，程序将由于运行时错误而失败:"forrtl:严重(408):要塞:(7):在调用c_f_pointer(c_p，f_p)"行尝试使用未与目标关联的指针F_P.
If I add the ‘(:)’ to the definition of f_p, the code compiles without error, but when I run it, the program fails with the run-time error: "forrtl: severe (408): fort: (7): Attempt to use pointer F_P when it is not associated with a target" at the line "call c_f_pointer(c_p, f_p)".
我尝试将c_p声明为数组("c_p(:)")，但在同一位置却遇到相同的错误.
I have tried declaring c_p as an array ("c_p(:)"), but I get the same error in the same place.
我还尝试将c_p用作子例程的参数–仍然仅使用整数:
I have also tried calling c_p as an argument to a subroutine – still only using integers:
! ps_test_pointers.f90
program foo
use, intrinsic :: iso_c_binding, only : c_ptr, &
c_f_pointer, &
c_int
implicit none
type(c_ptr) :: c_p!(:) ! <-------
integer(c_int), pointer :: f_p!(:) ! <-------
interface
subroutine foofunc(c_p) bind(c)
import :: c_ptr
implicit none
type(c_ptr) :: c_p!(:) ! <-------
end subroutine foofunc
end interface
call foofunc(c_p)
call c_f_pointer(c_p, f_p)
print *, f_p
end program foo
// ps_test_pointersC.cpp : 'Subroutine' only.
extern "C" {
int bar[3] = { 2, 3, 4 };
void foofunc(int *rtn) {
rtn = bar;
}
}
但是在C函数中创建的指针永远不会在返回时分配给c_p(因此从未定义f_p).
but the created pointer in the C function never gets assigned to c_p on return (hence f_p is never defined).
仔细阅读问题，希望我不会在编译器实现的前沿，并且在限制加紧但不能应对所有用例之间暴露出一个问题！
Reading around the problem, I hope I’m not at the bleeding edge of compiler implementation and have exposed a problem between restrictions tightening but not coping with all the use cases!
对此有解决方案吗?
推荐答案
RE是子例程方法，我认为我们可能需要将 c_p 声明为 int ** (而不是而不是C/C ++端的 int * )来通过参数关联(而不是函数返回值)获取 bar 的地址.像...
RE the subroutine approach, I think we probably need to declare c_p as int** (rather than int*) on the C/C++ side to get the address of bar via argument association (rather than function return value). So something like...
main.f90:
program foo
use, intrinsic :: iso_c_binding, only : c_ptr, &
c_f_pointer, &
c_int
implicit none
type(c_ptr) :: c_p
integer(c_int), pointer :: f_p(:)
integer(c_int) :: nsize
interface
subroutine foosub( c_p, nsize ) bind(c)
import :: c_ptr, c_int
implicit none
type(c_ptr) :: c_p !<-- sends the pointer to c_p
integer(c_int) :: nsize !<-- sends the pointer to nsize
end subroutine
end interface
call foosub( c_p, nsize )
call c_f_pointer( c_p, f_p, [nsize] )
print *, "nsize = ", nsize
print *, "f_p(:) = ", f_p(:)
end program
sub.cpp:
extern "C" {
int bar[3] = { 2, 3, 4 };
void foosub( int** rtn, int* nsize ) {
*rtn = bar;
*nsize = sizeof(bar) / sizeof(int);
}
}
编译&运行:
$ g++-10 -c sub.cpp
$ gfortran-10 -c main.f90
$ g++-10 main.o sub.o -lgfortran
$ ./a.out
nsize = 3
f_p(:) = 2 3 4
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