Multidimensional array in C++?

Question

Today, I have a general question about storing objects/structs or some other values in a multidimensional array.

The actual scenario is as follows, but I might need similar solutions in many other places, which is why I want to ask you about the best-practice to this.

Suppose we have a side scrolling game. Now I need to store information about the cells of the world in some kind of 2-dimensional array, where 0:0 would be the home-position. At the beginning of the game, I generate a small area of the world, say from -10:-5 to 10:5. The player could move left or right (and sometimes up and down), so I have to generate more world information when he reaches the edges of the world. Now my question: How am I supposed to store a 2-dimensional array with varying extremes? Are there any best practices around how to do this? What would you do?

Thanks again for all your help!

@H2CO3 And how would I ideally keep track of the dimensions? Say my field at one point stretches from -101:-18 to 55:12 or something. How do I determine where the information to cell 0:0 is stored? — Lars Ebert-Harlaar
– Lars Ebert-Harlaar, Commented Sep 29, 2013 at 19:00
using a variable. Of type size_t or int or whatever. And vector knows its size. — user529758
– user529758, Commented Sep 29, 2013 at 19:04
@H2CO3: vector<t>(dimension1*dimension2*dimension3*dimension4...), actually. — SigTerm
– SigTerm, Commented Sep 29, 2013 at 19:28
@H2CO3: Less allocations, no memory fragmentation/overhead, simpler resize. — SigTerm
– SigTerm, Commented Sep 29, 2013 at 19:30

Martin Beckett · Accepted Answer · 2013-09-29 19:00:12Z

4

Don't store it as an array, use a structure containing the coords and the value.

Then store those objects in a smarter structure - deque, list or tree depending on how they need to be searched.

answered Sep 29, 2013 at 19:00

Martin Beckett

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3 Comments

Lars Ebert-Harlaar Over a year ago

Cool, I did not know about deques before, they sound pretty handy. Thx!

Martin Beckett Over a year ago

@LarsEbert if you are going to move in any direction (rather than just scroll in 1d) then look at trees.

Lars Ebert-Harlaar Over a year ago

Okay, I just googled "trees", I do not know what I expected... But seriously, I understandy the definition of a (binary-)tree but I have no idea how to store the world in a tree.

SigTerm · Accepted Answer · 2013-09-29 20:01:26Z

1

Solution #1: use 1d array with size == dimension1*dimension2*dimension3*.... and emulate multidimensional array like that. You will have to write your own resize code (should be easy)
Solution #2: Use sparse array. A std::map<Coordinate, Value> will do.
Solution #3: Boost.MultiArray.
Solution #4: Don't store the world as N-dimensional array. Store objects as a list/deque/whatever, then use BSP tree, oct-trees, sweep and prune or space partitioning to quickly locate objects in visible area.

edited Sep 29, 2013 at 20:01

answered Sep 29, 2013 at 19:29

SigTerm

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