fortran - 如何在 Fortran 公共块中使用可分配字符？

Question

我试图在 Fortran 77 中的公共块内有一个可分配的字符。但编译器总是抱怨

Error: COMMON attribute conflicts with ALLOCATABLE attribute at (1)

我的代码是

      subroutine word()
          character (len = :), allocatable :: a
          common /a/ a
          a = 'word'
      end subroutine word

      program main
          character (len = :), allocatable :: a
          common /a/ a
          call word()
          print *, a
      end program main

我看到使它工作的唯一方法是不使用allocatable

      subroutine word()
          character * 4 :: a
          common /a/ a
          a = 'word'
      end subroutine word

      program main
          character * 4 :: a
          common /a/ a
          call word()
          print *, a
      end program main

但这会很麻烦，因为我必须提前知道字符的长度。

我怎么能allocatable在一个common街区工作？