c - 如何从由 iso_c_binding 的 Fortran 调用的 C 函数接收字符串？

Question

我想从 Fortran 调用 C 函数并接收在 C 函数中定义的字符串。我搜索过，但到目前为止我找不到一个有效的、直接的答案。

实际上我找到了一个解决方法:接收一个字符数组，然后使用内部函数 transfer将结果放入 Fortran 字符串中。
这是我的工作代码。

Fortran主程序:

program pr
    implicit none
    character(200) :: stringa

    call strfromc(stringa)
    write (6,*) 'FPR stringa: "', trim(stringa),'"'

    stop
end program pr

Fortran子程序:

subroutine strfromc(stringa)
    use iso_c_binding
    implicit none

    character(200) :: stringa

    interface
        subroutine getstrfromc(ld,d) bind(c,name='getString')
            import :: c_int, c_ptr
            integer(c_int) :: ld
            type(c_ptr), value :: d
        end subroutine getstrfromc
    end interface

    ! declare a character array of type c_char and sufficient length:
    character(c_char), dimension(200), target :: d1

    integer :: ld1 ! will contain the string length
    integer :: i

    ! the C pointer of character array d1 is passed:
    call getstrfromc(ld1, c_loc(d1))

    ! read the first ld1 elements of array d1 as a character string, which will be returned:
    stringa= transfer(d1(1:ld1), stringa)

    write (6,*) 'SF d1: ', (d1(i),i=1,ld1)
    write (6,*) 'SF stringa: "', trim(stringa),'"'
    write (6,*) ''

    return
end subroutine

C函数:

#include <stdio.h>
#include <string.h>

void getString(int * lw, char * w) {
    printf("Enter a string:\n");
    scanf("%[^\n]", w); //scanning the whole string, including the white spaces

    *lw= strlen(w);

    printf("C: w: %s\n", w);
    printf("C: lw: %d\n", *lw);
    printf("\n");

    return;
}

任何人都可以提出更直接的方法吗？

Answer 1

为什么不简单地使用 C_CHAR种类？我“压缩”了你的代码:

program main
  use, intrinsic :: iso_c_binding, only: C_INT, C_CHAR
  implicit none
  integer         :: lw ! will contain the string length
  character(256)  :: w = "" ! will contain the string; Initialize to empty

  ! C interface
  interface
    subroutine getstrfromc( lw, w ) bind( c, name='getString' )
      import :: C_INT, C_CHAR
      implicit none
      integer(C_INT), intent(out)     :: lw
      character(C_CHAR), intent(out)  :: w(*)
    end subroutine getstrfromc
  end interface

  ! In Fortran variables are passed by default as "pointers".
  call getstrfromc( lw, w )

  ! Write string
  write (*,*) "Fortran: w: ", trim(w)
  write (*,*) "Fortran: lw:", lw

end program main

C 函数保持不变。