arrays - 错误 : The part-name to the right of a part-ref with nonzero rank has the ALLOCATABLE attribute

Question

我想使用子例程 sum_real 访问数组派生类型中数组的元素。即:对所有人的权重中的第一个条目求和。

type my_type
   real, dimension(:), allocatable :: weight
   real :: total_weight
end type my_type

type (my_type), dimension (:), allocatable :: people
type (my_type) :: answer

allocate (people (2))
allocate (people (1)%weight(2))
allocate (people (2)%weight(2))

people (1) % weight(1) = 1
people (2) % weight(1) = 1
people (1) % weight(2) = 3
people (2) % weight(2) = 3

call sum_real ( people (:) % weight(1), answer % total_weight )

我想要做的类似于 Array of derived type: select entry中找到的答案，除了我在数组派生类型而不是单个元素中分配了一个数组。

但是，我收到一个编译器错误:

error #7828: The part-name to the right of a part-ref with nonzero rank has the ALLOCATABLE attribute (6.1.2).   [WEIGHT]

Answer 1

如果您的组件是可分配的，则您尝试的操作是不可能的。引用( 6.1.2 )实际上是对官方标准文档的引用，禁止这样做。

原因很简单，可分配的组件(标量或数组)存储在与派生类型本身不同的内存部分。因此，如果你写

sum(people%total_weight)

或者

people%total_weight = 0

没问题， total_weight不可分配，它存储在派生类型中，编译器只是进入一个简单的循环并将一个又一个字段设置为零。可以知道每个 %totalweight的地址预先。

另一方面

sum(people%weight)

或者

people%weight = 0

每个 %weight存储在其他地方，您没有任何简单的公式来计算每个 %weight(i) 的位置.

如果可能，解决方案是固定数组的大小

real, dimension(2) :: weight

或使用 do 循环

s = 0
do i = 1, size(people)
  S = S + sum(people(i)%weight)
end do