创建具有300万个元素的双数组 [英] Creating a double array with 3 million elements

问题描述

我正在尝试创建一个包含300万个随机元素的双精度数组:

I am trying to create an array of doubles with 3 million random elements:

#include <iostream>
#include <cstdlib>
#include <random>
#include <ctime>

using namespace std;

int main(int argc, const char * argv[]) {

    // generating random numbers
    mt19937 rng_engine(0); // seed = 0
    uniform_real_distribution<double> dist2(0,10);    

    clock_t begin = clock();

    // create a random 2d array 1 million x 3
    double coords[1000000][3];
    for (int i=0; i<1000000; i++) {
        for (int j= 0; j<3; j++) {
            coords[i][j] = dist2(rng_engine);
            //cout << "i = " << i << ", j = " << j << ", val = " << coords[i][j] << endl;
        }
    }

    clock_t end = clock();
    double elapsed = double(end - begin) / CLOCKS_PER_SEC;

    cout << "elapsed: " << elapsed << endl;

    return 0;
}

当我尝试在Xcode中运行此代码时，我得到 EXC_BAD_ACCESS(代码= 2，地址= 0x7fff5e51bf9c).我试图编译它并在命令行中运行它，这给了 Segmentation错误:11 .当我将数组大小更改为 [100000] [3] 时，使元素数达到300,000，代码开始运行.我不明白的是为什么拥有300万双打是一个问题.数组大小不是24 MB吗?(8个字节* 3,000,000 = 24 MB)我缺少什么?

When I try to run this in Xcode, I get EXC_BAD_ACCESS (code=2, address=0x7fff5e51bf9c). I tried to compile it and run it in the command line, which gave Segmentation fault: 11. When I change the array size to [100000][3], making the number of elements 300,000, the code runs. What I don't understand is why is it a problem to have 3 million doubles. Wouldn't the array size be 24 MB? (8 bytes * 3,000,000 = 24 MB) What am I missing?

推荐答案

您几乎肯定会溢出堆栈.

You're almost certainly overflowing the stack.

避免这种情况的明显选择是使数组 static (当它位于 main 中时实际上并没有太大变化，但是通常以不同的方式分配它)或(通常更好)改为使用 std :: vector .

Obvious choices to avoid that would be to make the array static (doesn't really change much when it's in main, but typically allocates it differently) or (usually better) use an std::vector instead.

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