1

I'm making a game in Node.js with a C++ component. This C++ component is invoked often (as a subprocess) and is a bottleneck. Thus, I hardcoded its assets as const arrays to make it run faster.

However, I noticed that my C++ code takes a long time to compile. Following is a demonstration of the problem:

#include <iostream>
#include <vector>
#define d 3,
#define _ 999,
// an array holding some game assets
const std::vector<std::vector<std::vector<int>>> STRUCTURES {

    { // you should make 80 copies of this paragraph before benchmarking
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ d d d d d d d _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
    },

};
int main(int argc, char **argv){
    // prevent optimizer from ignoring the big array
    std::cout << STRUCTURES.size() << std::endl;
    return 0;
}

If you repeat the middle paragraph 80 times, it'll be comparable in size to my C++ program. I compile with g++ test.cpp -O3 and it takes 36 seconds to compile. I don't understand why this is so slow. Is there something I can change to make it compile much faster?

Maze
  • 63
  • 6
  • 3
    It's not an array, it's a vector. Why not use `std::array`? – Barmar Jul 02 '20 at 01:12
  • 1
    Why don't you move this into a separate `.cpp` file that you link with the rest of the application? That way you won't need to recompile it while you're debugging the rest. – Barmar Jul 02 '20 at 01:14
  • 2
    It took only 4 seconds for gcc 10 to compile this work of art, but without any optimization flags. But, yes, with `-O2`, this beauty took 38 seconds. You have to keep in mind that `std::vector` is a template, and this expands to a crapton of code, that you've instructed your poor compiler to analyze six ways to Sunday. – Sam Varshavchik Jul 02 '20 at 01:20
  • wow, I tried with std::array and it is significantly faster now, it only takes 0.4 seconds! It seems the problem really was in std::vector. I was generalizing too much. Thank you! I will make this into an answer and accept it, unless one of you wants to do that? – Maze Jul 02 '20 at 01:23
  • 1
    See https://mklimenko.github.io/english/2018/11/26/stdembed-for-the-poor/ – sehe Jul 02 '20 at 01:30
  • 1
    In addition to @Barmar ,How about making it constexpr array? It may speed up the application further.. – K.R.Park Jul 02 '20 at 01:39

2 Answers2

2

Not using dynamic allocation helps:

template <typename T, int a, int b, int c>
using sprites = std::array<std::array<std::array<T, c>, b>, a>;

But not allocating at all must be faster. Now I don't know about you, but I find getting the initializers correct and lined up Very Tedious(TM) so, let's not:

// an array holding some game assets
static constexpr char STRUCTURES[] {
    // pos 0
    "_____________________________________"
    "_____________________________________"
    "_____________________________________"
    "_____________________________________"
    "_________________________ddddddd_____"
    "______________________ddddddddddd____"
    "_____________________ddddddddddddd___"
    "____________________dddddddddddddd___"
    "___________________ddddddddddddddd___"
    "__________________dddddddddddddddd___"
    "_________________dddddddddddddddd____"
    "________________ddddddddddddddddd____"
    "_______________ddddddddddddddddd_____"
    "______________ddddddddddddddddd______"
    "____________dddddddddddddddddd_______"
    "___________dddddddddddddddddd________"
    "__________ddddddddddddddddddd________"
    "_________ddddddddddddddddddd_________"
    "________ddddddddddddddddddd__________"
    "________ddddddddddddddddddd__________"
    "_______dddddddddddddddddddd__________"
    "______dddddddddddddddddddd___________"
    "______dddddddddddddddddddd___________"
    "______dddddddddddddddddddd___________"
    "______ddddddddddddddddddd____________"
    "______ddddddddddddddddddd____________"
    "______dddddddddddddddddd_____________"
    "______ddddddddddddddddd______________"
    "_______ddddddddddddddd_______________"
    "________ddddddddddddd________________"
    "_________ddddddddddd_________________"
    "___________ddddddd___________________"
    "_____________________________________"
    "_____________________________________"
    "_____________________________________"
    "_____________________________________"
    "_____________________________________"
    // pos 1
    // ....
    // ....
    // ....
    "_____________________________________"
    "_____________________________________"
    // pos 81
    "_____________________________________"
    "_____________________________________"
    "_____________________________________"
    "_____________________________________"
    "_________________________ddddddd_____"
    "______________________ddddddddddd____"
    "_____________________ddddddddddddd___"
    "____________________dddddddddddddd___"
    "___________________ddddddddddddddd___"
    "__________________dddddddddddddddd___"
    "_________________dddddddddddddddd____"
    "________________ddddddddddddddddd____"
    "_______________ddddddddddddddddd_____"
    "______________ddddddddddddddddd______"
    "____________dddddddddddddddddd_______"
    "___________dddddddddddddddddd________"
    "__________ddddddddddddddddddd________"
    "_________ddddddddddddddddddd_________"
    "________ddddddddddddddddddd__________"
    "________ddddddddddddddddddd__________"
    "_______dddddddddddddddddddd__________"
    "______dddddddddddddddddddd___________"
    "______dddddddddddddddddddd___________"
    "______dddddddddddddddddddd___________"
    "______ddddddddddddddddddd____________"
    "______ddddddddddddddddddd____________"
    "______dddddddddddddddddd_____________"
    "______ddddddddddddddddd______________"
    "_______ddddddddddddddd_______________"
    "________ddddddddddddd________________"
    "_________ddddddddddd_________________"
    "___________ddddddd___________________"
    "_____________________________________"
    "_____________________________________"
    "_____________________________________"
    "_____________________________________"
    "_____________________________________"
};

Naive Indexing Helper

Now, of course, you wanted ints and mapped the chars to certain values (like 3 and 999 in this case). To get that, we can use a naive indexing helper:

struct Helper {
    constexpr int operator()(int a, int b, int c) const {
        switch (auto ch = STRUCTURES[a*37*37 + b*37 + c]) {
            case 'd': return 999;
            case '_': return 3;
        }
        return 0;
    }
};

Now we can write main to print a randomm "glyph", "sprite" or whatever those resources are:

#include <iostream>
#include <iomanip>

int main() {
    auto a = rand() % 81;

    Helper index;
    for (int b = 0; b < 37; ++b) {
        for (int c = 0; c < 37; ++c)
            std::cout << std::setw(4) << index(a, b, c);
        std::cout << "\n";
    }
}

It prints (I had 81x the same "image"):

   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999 999 999 999 999   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3 999 999 999 999 999 999 999   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3

Non-Naive Indexing Helper: Boost MultiArray

Much less code, much more features. Now you can use .size() and ranged-for:

#include <boost/multi_array.hpp>

int main() {
    constexpr std::array shape {81,37,37};
    boost::const_multi_array_ref<char, 3> view(STRUCTURES, shape);

    auto const& sprite = view[rand() % view.size()];
    for (auto const& row : sprite) {
        for (auto const& cell : row)
            printf("%4d", (cell=='d'? 999 : 3));
        putchar('\n');
    }
}

Full Demo Live

  • Naive indexing Helper version: Live On Coliru

    Compilation: (on coliru!)

     real    0m0.562s
 user    0m0.432s
 sys 0m0.124s

    Runtime (on coliru!):

     real    0m0.005s
 user    0m0.000s
 sys 0m0.004s

  • Boost Multi-Array version: Compiler Explorer/Coliru

Executable size is 118k (GCC) or 119k (clang) on my system (both approaches).

sehe
  • 374,641
  • 47
  • 450
  • 633
  • Here it is on [Compiler Explorer](https://godbolt.org/z/_eQe3y) showing the code gen (replaced `iostream` with `cstdlib` for the purpose) – sehe Jul 02 '20 at 02:09
  • Also added a version that uses `boost::const_array_ref` instead of writing that silly `Helper` and doing manual index calculations: **[Compiler Explorer](https://godbolt.org/z/XZVEPk)**/**[Coliru](http://coliru.stacked-crooked.com/a/6887b09d7d54a76f)** Now you can use `.size()` and ranged-for. – sehe Jul 02 '20 at 02:24
1

The solution, as suggested by Barmar and Sam Varshavchik, is to avoid std::vector.

There are too many vectors and the optimizer is taking a lot of time to deal with that. std::array can be used instead. For this sample, that means:

#include <iostream>
#include <vector>
#include <array>
#define d 3,
#define _ 999,
// an array holding some game assets
const std::vector<std::array<std::array<int,37>,37>> STRUCTURES {

    {{ // you should make 80 copies of this paragraph before benchmarking
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ d d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ d d d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ d d d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ d d d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ d d d d d d d d d d d _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ d d d d d d d _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
        { _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ },
    }},

};
int main(int argc, char **argv){
    // prevent optimizer from ignoring the big array
    std::cout << STRUCTURES.size() << std::endl;
    return 0;
}

Notice that I still used a single std::vector for the outermost dimension. This does not present a significant overhead when compiling.

Maze
  • 63
  • 6