如何在C ++中增加和缩小双指针动态数组？

Question

I'm learning C++ and I'm expected to use a double pointer to build a dynamic array of objects that grows and shrinks as elements are added and removes from the array.

I can create the array like so:

Person** people = new Person*[10];

And add objects like so:

people[0] = new Person(“Luke”);
people[1] = new Person(“Han”);
people[2] = new Person(“Leia”);

And delete objects like so:

delete people[1]
people[1] = null;

(At least I think that's correct.)

But I'm stuck on several things...

Questions:

Once the array is full with 10 items, how do I dynamically add more space for additional objects? In fact, I'm thinking the array should probably have a size of 0 before the first item is added; how do I do that?

Similarly, when I delete an item (like when I delete people[1], above), how do I shrink the array down to a minimum size? Like, how do I make the object at people[2] move to the position of people[1]?

Any suggestions or help is greatly appreciated, thanks!

rh

Answer 1

您需要创建一个更大的新数组，并从当前数组中复制数据并取消分配。

Answer 2

You need to implement reallocation .

Basically you create a second, bigger (or smaller) array, copy the existing elements there, and then discard the old array.

Do note, that you just need to copy the pointers. The objects themselves do not need to change.

Under the hood, std::vector does the same thing.

A common practice, when creating a bigger array, is to multiply its size by a factor somewhere between 1.5-2.

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When removing an element, you need to shift all elements at higher indeces one element lower. Again, you just need to move the pointers, not the objects themselves.