英文:
If a struct has a Vector field, does it get allocated on the heap?
问题
Train 结构体将被分配在堆栈上，但它的字段 passenger_ids 会指向堆上的数据，因为它是 Vector 类型，Vector 内的元素通常会分配在堆上。
英文:
Suppose I have a struct Train which contains a field called passenger_ids which itself represents a Vector of passenger identifiers.
struct Train {
passenger_ids: Vector<u32>
}
Would Train be allocated on the heap since it holds a field of type Vector (which is allocated on the heap)? Or would it instead be allocated on the stack and the field point towards the heap?
答案1
得分: 4
No, a train would not be allocated on the heap, and no a vector is not allocated on the heap.
A Vec is a normal structure which contains a pointer to a heap allocation. The Train, and the Vec it contains, will be allocated as a single unit wherever they are put (whether that's on the stack, or on the heap if Box-ed, or somewhere else).
The Vec will then, if and when items get added to it, create a heap allocation and put the items there.
英文:
> Would Train be allocated on the heap since it holds a field of type Vector (which is allocated on the heap)? Or would it instead be allocated on the stack and the field point towards the heap?
No, a train would not be allocated on the heap, and no a vector is not allocated on the heap.
A Vec is a normal structure which contains a pointer to a heap allocation. The Train, and the Vec it contains, will be allocated as a single unit wherever they are put (whether that's on the stack, or on the heap if Box-ed, or somewhere else).
The Vec will then, if and when items get added to it, create a heap allocation and put the items there.
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