C++ const数组编译时间长
[英]C++ long compilation time of const array
问题描述
I'm making a game in Node.js with a C++ component.
我正在 Node.js 中使用 C++ 组件制作游戏。 This C++ component is invoked often (as a subprocess) and is a bottleneck.这个 C++ 组件经常被调用（作为子进程）并且是一个瓶颈。 Thus, I hardcoded its assets as const arrays to make it run faster.因此，我将其资产硬编码为 const arrays 以使其运行得更快。
However, I noticed that my C++ code takes a long time to compile.但是，我注意到我的 C++ 代码需要很长时间才能编译。 Following is a demonstration of the problem: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;
}
If you repeat the middle paragraph 80 times, it'll be comparable in size to my C++ program.如果将中间段落重复 80 次，它的大小将与我的 C++ 程序相当。 I compile with g++ test.cpp -O3 and it takes 36 seconds to compile.我用g++ test.cpp -O3编译，编译需要 36 秒。 I don't understand why this is so slow.我不明白为什么这么慢。 Is there something I can change to make it compile much faster?有什么我可以改变的，让它编译得更快吗？
2 个解决方案
解决方案1
2 2020-07-02 01:59:10
Not using dynamic allocation helps:不使用动态分配有助于：
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.但是根本不分配必须更快。 Now I don't know about you, but I find getting the initializers correct and lined up Very Tedious(TM) so, let's not:现在我不了解你，但我发现让初始化程序正确并排列非常乏味（TM）所以，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___________________"
"_____________________________________"
"_____________________________________"
"_____________________________________"
"_____________________________________"
"_____________________________________"
};
Naive Indexing Helper朴素的索引助手
Now, of course, you wanted ints and mapped the chars to certain values (like 3 and 999 in this case).现在，当然，您需要整数并将字符映射到某些值（如本例中的 3 和 999）。 To get that, we can use a naive indexing helper: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;
}
};
Now we can write main to print a randomm "glyph", "sprite" or whatever those resources are:现在我们可以编写main来打印随机的“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";
}
}
It prints (I had 81x the same "image"):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
Non-Naive Indexing Helper: Boost MultiArray非天真的索引助手：Boost MultiArray
Much less code, much more features.更少的代码，更多的功能。 Now you can use .size() and ranged-for:现在您可以使用.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');
}
}
Full Demo Live完整演示现场
Naive indexing
Helperversion: Live On ColiruNaive indexing Helper版本： Live On ColiruCompilation: (on coliru!)
编译：（关于大肠杆菌！）real 0m0.562s user 0m0.432s sys 0m0.124sRuntime (on coliru:):
运行时（在 coliru 上:)：real 0m0.005s user 0m0.000s sys 0m0.004sBoost Multi-Array version: Compiler Explorer / Coliru
Boost Multi-Array 版本： Compiler Explorer / Coliru
Executable size is 118k (GCC) or 119k (clang) on my system (both approaches).我的系统上的可执行文件大小为 118k (GCC) 或 119k (clang)（两种方法）。
解决方案2
1 2020-07-02 01:40:11
The solution, as suggested by Barmar and Sam Varshavchik, is to avoid std::vector.正如 Barmar 和 Sam Varshavchik 所建议的，解决方案是避免使用 std::vector。
There are too many vectors and the optimizer is taking a lot of time to deal with that.向量太多，优化器要花很多时间来处理。 std::array can be used instead.可以使用 std::array 代替。 For this sample, that means: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;
}
Notice that I still used a single std::vector for the outermost dimension.请注意，我仍然使用单个 std::vector 作为最外层维度。 This does not present a significant overhead when compiling.这在编译时不会产生很大的开销。
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