Question

Imagine there’s a fixed and constant set of ‘options’ (e.g. skills). Every object (e.g. human) can either have or not have any of the options.

Should I maintain a member list-of-options for every object and fill it with options?

OR:

Is it more efficient (faster) to use a bitarray where each bit represents the respective option’s taken (or not taken) status?

-edited:-

To be more specific, the list of skills is a vector of strings (option names), definitely shorter than 256.
The target is for the program to be AS FAST as possible (no memory concerns).

Answer 1

That rather depends. If the number of options is small, then use several bool members to represent them. If the list grows large, then both your options become viable:

• a bitset (which an appropriate enum to symbolically represent the options) takes a constant, and very small, amount of space, and getting a certain option takes O(1) time;
• a list of options, or rather an std::set or unordered_set of them, might be more space-efficient, but only if the number of options is huge, and it is expected that a very small number of them will be set per object.

When in doubt, use either a bunch of bool members, or a bitset. Only if profiling shows that storing options becomes a burden, consider a dynamic list or set representation (and even then, you might want to reconsider your design).

Edit: with less than 256 options, a bitset would take at most 64 bytes, which will definitely beat any list or set representation in terms of memory and likely speed. A bunch of bools, or even an array of unsigned char, might still be faster because accessing a byte is commonly faster than accessing a bit. But copying the structure will be slower, so try several options and measure the result. YMMV.