Question

I have a system where I need to get “codes” for specific positions. There is a constant number of positions, 1 to 40, however, each position can have different number of codes (from 2 to 20). The container is constant, it needs to be defined, then is just used to look up positions for the rest of the program.

For example, I need to be able to do something like myCodes.at(position3) and get {1, 3, 9, 23, 52} and myCodes.at(position7) and get {23, 52}

So, the outer container is of constant size, but the inner container can vary in size from 2 to 20. The way I know how to do this is using arrays, and just make the second dimension the max possible size (20): const int myCodes[40][20], then just “pad” the inner array with extra 0’s.

However, this feels really wasteful, especially because many of the inner arrays would only be holding 2 elements. I am also working on learning C++11, so I would prefer a “modern” solution if there is one.

Answer 1

This is likely what you want:

std::array<std::vector<code>, const_size>

The outer is constant and the inner is dynamic.

Having both be constant and using padding will be faster, but much uglier and so don’t try it at first. 18*20 unused ints is not much of a waste on modern hardware.