Bug when redimensioning multi-dimension arrays?

[12centuries]

The manual for Quick- and QBasic: "Neither the type nor the dimension of an array may be changed."

I don't know what you're doing, but I don't think it's solid.

When reducing an array dimension, DATA LOSS OCCURS.

Well, what do you know! If I reduce a 5X5 array to 4X4, data is lost... Thanks!

Let's see where this ends up! 

Quite right, QBasic and QuickBasic were much more limited than even PDS/QBX were, which allowed the size of dimensions to be changed: "Although you can change the size of an array's dimensions with the REDIM statement, you can not change the number of dimensions." (Microsoft BASIC Professional Development System 7.1 — Basic Language Reference, 1989, p. 289).

So many languages have the ability to change array dimensions, like python's del statement, javascript's slice method, the Arrays.copyOf method in Java, or std::vector's resize method in C++. It's too bad Q[uick]Basic didn't have something. I think the _PRESERVE keyword is a credit to the QB64 developers for including it.

I suppose that warning was a bit obvious, It's a long-ingrained habit of mine to ensure that any potential loss of data is fully documented so that anyone who reuses my code would have a full grasp of the consequences.


So here's what I'm doing...this code is part of a game with multiple levels that are loaded from user-editable text files. The dimensions of the maps are not known until read, and rather than read through the file twice (first a parsing read, then array dimensioning, then a loading read), I opted to use a more adaptive approach which adjusts the array size as it loads.

When all is done, the array is sometimes larger than required, so I reduce it. While it's not intended to pare down existing data from an array, you could use it for that, so I think the warning is warranted.