c++中计算程序执行时间

#include<iostream>
#include<time.h>
using namespace std;

int main()
{
    clock_t t1 = clock();

    for (int i = 0; i < 100000000; i++);
    
    clock_t t2= clock();

    cout << "time " << t2 - t1 << endl;
}