C/C++のタイマー

#include <iostream>
#include <ctime>
#include <unistd.h>
using namespace std;

int main() {

 clock_t st = clock();
 for( long l = 0;l < 100000000;l++ );
 clock_t end = clock();
 cout << st << ":" << end << endl;
 cout << "elapsed - " << (end - st) * 1000 / CLOCKS_PER_SEC << endl;
 return 0;

}