const 数组的 C++ 编译时间长

Question

我正在 Node.js 使用 C++ 组件制作游戏。这个 C++ 组件经常被调用（作为子进程）并且是一个瓶颈。因此，我将其资产硬编码为 const 数组，以使其运行更快。

但是，我注意到我的 C++ 代码需要很长时间才能编译。以下是问题的演示：

#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;
}

如果您将中间段落重复 80 次，它的大小将与我的 C++ 程序相当。我用 g++ test.cpp -O3 编译，编译需要 36 秒。我不明白为什么这么慢。有什么我可以改变的，让它编译得更快吗？

Answer 1

按照 Barmar 和 Sam Varshavchik 的建议，解决方案是避免 std::vector。

向量太多，优化器需要花费大量时间来处理。 std::array 可以代替。对于此示例，这意味着：

#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;
}

请注意，我仍然使用单个 std::vector 作为最外层维度。这在编译时不会产生明显的开销。

Answer 2

不使用动态分配有帮助：

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

但完全不分配肯定更快。现在我不了解你，但我发现初始化程序正确并且排列非常乏味 (TM) 所以，让我们不要：

// 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___________________"
    "_____________________________________"
    "_____________________________________"
    "_____________________________________"
    "_____________________________________"
    "_____________________________________"
};

朴素的索引助手

现在，当然，您需要整数并将字符映射到某些值（例如本例中的 3 和 999）。为此，我们可以使用一个简单的索引助手：

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;
    }
};

现在我们可以编写 main 来打印随机“字形”、“精灵”或任何这些资源：

#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";
    }
}

它打印（我有 81 倍相同的“图像”）：

   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3   3
   3   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

非朴素索引助手：Boost MultiArray

更少的代码，更多的功能。现在你可以使用 .size() 和 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');
    }
}

现场完整演示

朴素索引 Helper 版本：Live On Coliru

编译：（在 coliru 上！）
```
 real    0m0.562s
 user    0m0.432s
 sys 0m0.124s
```
运行时（在 coliru 上！）：
```
 real    0m0.005s
 user    0m0.000s
 sys 0m0.004s
```
提升多阵列版本：Compiler Explorer/Coliru

我的系统（两种方法）上的可执行文件大小为 118k (GCC) 或 119k (clang)。

const 数组的 C++ 编译时间长

C++ long compilation time of const array

c++

arrays

vector

constants

compilation-time

朴素的索引助手

非朴素索引助手：Boost MultiArray

现场完整演示