Use std::vector instead of dynamic C-Array

[adrido]

Fixes #6740

I'm wondering, if it would possible/better to use a dynamic vector and floors.size() instead of num_floors and num_ceilings and a fixed vector.
But I does not want to break existing code and this PR is only meant to fix the failing build not for doing improvements.

[SmallJoker]

Pointer misplaced. u16 *num_floors, same for num_ceilings

[SmallJoker]

I suppose the C-style arrays were used for speed reasons, as the maximal size of the data amount is known. (ask @paramat ?)
You could still allocate the memory directly using s16 *floors = new s16[size] + delete[] floors or std::array<s16, size> floors.

[paramat]

Yes that's my code, i was unsure whether to use a vector instead of an array. I don't know of any advantage to an array, and vectors are used in most other places.
'floors' and 'ceilings' arrays are mostly used independently, one or the other, rarely both at the same time.

Will test.

[adrido]

I suppose the C-style arrays were used for speed reasons, as the maximal size of the data amount is known. (ask @paramat ?)
You could still allocate the memory directly using s16 *floors = new s16[size] + delete[] floors or std::array<s16, size> floors.

Thanks, I know. Its just my suggestion to fix #6740 . I don't know whether this function is time critical or not. A vector is just a more secure variant (and not necessary slower at all). Feel free to fix #6740 with another way. Every variant would fine for me as long as it fixes #6740. The merge process might be faster if a coredev is doing this.

[paramat]

I've seen vector used in many places in mapgen so i doubt it's slower, or significantly slower. I probably should have used vector in my PR anyway.

[paramat]

I'm no expert concerning the relative advantages of one against the other.

[adrido]

Thanks. A probably interesting article of C-Array vs std::array vs std::vector might be this by Bjarne Stroustrup: http:https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#slcon1-prefer-using-stl-array-or-vector-instead-of-a-c-array

[paramat]

Good, vector is fine for me.

[adrido]

@paramat I added some improvements that got possible due to the usage of vectors. Could you please test it again?

[paramat]

Interesting, i'll rereview to understand and then retest. Removed my +1 for now.

[paramat]

Ceiling decorations are not working, see line comment. My fix works.
👍 once fixed.

[paramat]

ceilings.push_back(y + 1);

[nerzhul]

it's slower than C style array or std::array if no resize is done before passing them, please resize before sending the vectors
Don't forget std::vector push_back (or emplace_back) triggers a memory copy if it's full because std::vector is memory adjacent

[adrido]

Thanks for reviewing. Done.
I just want to note:

1. ) std::array will not work here too, because size is still not const (at compile time). GCC or Clang may support it, but its not official standard of C++

2. )
   Stroustrup:

   People sometimes worry about the cost of std::vector growing incrementally. I used to worry about that and used reserve() to optimize the growth. After measuring my code and repeatedly having trouble finding the performance benefits of reserve() in real programs, I stopped using it except where it is needed to avoid iterator invalidation (a rare case in my code). Again: measure before you optimize.

   http:https://www.stroustrup.com/bs_faq2.html#slow-containers

[paramat]

Will retest then merge.

[paramat]

Tested and fine 👍

Done.