c++ 栈内数组读写效率 v.s. 堆上数组读写效率

函数内定义的数组都在栈内存上。

new 出来的数组在堆内存上（栈上的指针指向它们）。

想知道这两种方法定义的数组的读写效率，写了个小实验程序：

#include<iostream>
using namespace std;

#include<cmath>
#include<time.h>

#define n 1000

int main(){

    int a[n][n];

    int repeat1 = 1E1;
    clock_t t_start = clock();
    for(int i=0;i<repeat1;i++){
        for(int p=0;p<n;p++)
            for(int q=0;q<n;q++)
                a[q][p]=p;
    }
    clock_t t_end = clock();
    cout<<" It took me "<<(double)(t_end - t_start)/CLOCKS_PER_SEC<<" s to read stack memory "<<repeat1<<" times repeatedly"<<endl;

    int **b = new int *[n];
    for(int i=0;i<n;i++)
        b[i] = new int [n];
    int repeat2 = repeat1;
    t_start = clock();
    for(int i=0;i<repeat2;i++){
        for(int p=0;p<n;p++)
            for(int q=0;q<n;q++)
                b[q][p]=p;
    }
    t_end = clock();
    cout<<" It took me "<<(double)(t_end - t_start)/CLOCKS_PER_SEC<<" s to read heap memory "<<repeat2<<" times repeatedly"<<endl;

    for(int i=0;i<n;i++)
        delete [] b[i];
    delete [] b;
    return 0;
}

跑出来的结果是

 It took me 0.03125 s to read stack memory 10 times repeatedly
 It took me 0.03125 s to read heap memory 10 times repeatedly

似乎差不多。所以这两种方法，只有征用内存时效率有区别（上一个随笔中，栈上征用和释放，只用了堆上的 1E-6 的时间），读写没有多大区别？