vlax-make-safearray Problem

irneb · 发表于 2022-7-6 08:02:23

That is actually a reason NOT to use an array and to rather use a linked list. Growing / shrinking arrays is a very wasteful operation, whereas growing / shrinking lists is next to simply assigning to a variable.

Bill Tillman · 发表于 2022-7-6 08:07:24

You're absolutely right about that. I was toying around with a list method and got that working rather quickly.

F.Y.I. this method of using an array was working but when the quantity was an odd number the code I wrote was setting the boundary ok, but the nature of the code was that it would try to assign a value out of the bounds. My fix for that was just to allow the bounds of the array to be a little larger than needed, usually only by one element. And since this program was designed to run low and fast, and once it was completed it was done, the elements of the array would never need to be changed. Still I agree with everyone that the list method is a bit cleaner and easier to work with. In fact I used Find/Replace to change the code and switching from one the other took only a minute or two. I still have this block of code in it's own file and it gets called on demand and only if it's needed.

Learning something new each day keeps the mind young.

irneb · 发表于 2022-7-6 08:10:46

That's the usual fix for this scenario. All structures like collections use either linked lists, or such "growable" arrays as their base structure. If they use arrays they tend to keep the array slightly (or sometimes a lot) larger than the actual needed size. The most usual method is to grow the array to double its current size when its bounds is reached - this is so the extremely inefficient recreation of the array is not done many times over.
Note you need a separate variable to keep track of how many items are in fact used, since the bounds only shows "available-space" not "used-space". Some designs use one of the slots of the array to keep track of such. E.g. a Pascal String is an array of 256 bytes, the 1st of which contains the number of used characters. Another alternative is doing something similar to a C-String, where the last used slot contains a null value to indicate a "stop" - but this only works is null is not a valid normal value.

E.g. say the array bounds is (0 . 7), and you've used all 8 items from that. When you add another, you make a new array of (0 . 15), then copy each item from the old array into the new one, then add the new item. Then discard the old array. This is literally what happens with such "growable" arrays. Some implementations "might" be able to grow the array if the physical ram "in-front" of the array is not used by something else - but such happens very rarely.

[编程交流] vlax-make-safearray Problem

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