c++ - 使用 time() 函数计算执行时间

Question

我被分配了以下家庭作业，

Write a program to test on your computer how long it takes to do nlogn, n2, n5, 2n, and n! additions for n=5, 10, 15, 20.

我写了一段代码，但执行时间一直为 0。谁能帮我解决这个问题？谢谢

#include <iostream>
#include <cmath>
#include <ctime>
using namespace std;
int main()
{
 float n=20;
 time_t start, end, diff;
  start = time (NULL);
  cout<<(n*log(n))*(n*n)*(pow(n,5))*(pow(2,n))<<endl;
  end= time(NULL);
 diff = difftime (end,start);
 cout <<diff<<endl;
 return 0;
}

Answer 1

比具有秒精度的 time() 更好的是使用毫秒精度。一种便携的方式是例如

int main(){
clock_t start, end;
double msecs;

start = clock();
/* any stuff here ... */
end = clock();
msecs = ((double) (end - start)) * 1000 / CLOCKS_PER_SEC;
return 0;
}