每个 class 实例具有不同大小的数组 class 成员

Question

I would like to have a class that contains an array member, but the constructor lets me set the size of an array member.

Is this doable? I do not thing I need dynamic allocation, since once the class instances are created, there is no need for the array to change size, it is just that each class instance will have a different size.

Answer 1

Despite several comments suggest that this would be impossible, it is actually not impossible.

The simplest way, of course, is to use an indirection and allocate the array during construction just the normal way (with a = new type[size] and calling delete[] a - not delete a - in the destructor).

But if for some reason you really do not want to have the array data being allocated separately from your object, you can use placement-new to construct your object into a pre-allocated buffer that is large enough to contain all your elements. This avoids a separate allocation for your array and you can still have dynamic size.

I would not recommend using this technique, though, unless you really have a demanding use case for it.